ACIDS, BASES AND SALTS

Transcription

1 Chemistry Scope Document THERMAL PHYSICS UNIT-1 ACIDS, BASES AND SALTS Learning outcomes - Core At the end of this unit, students should be able to vexplain, how solids, liquids and gases expand. vunderstand the importance and significance of thermal expansion in different practical situations. vdefine specific heat capacity and specific latent heat. vsolve numericals based on specific heat capacity and specific latent heat. vunderstand, how heat gets transferred through solids, liquids and gases. vdifferentiate between conduction, convection and radiation. vlearn about different methods of heat transfer in different situations in nature and man made devices. 1

2 CHEMISTRY

3 Chemistry ACIDS, BASES AND SALTS Syllabus Coverage S Y L L A B U S 2Characteristic chemical and physical properties of acids and bases. 2Strong and weak acids and bases. 2Acids and bases in our daily routine. 2Nature of oxides. 2Preparation of salts and their nature. Core 2Properties of carbon dioxide, hydrogen and chlorine gases. Extension 2Calculation of ph of a given solution. 2Properties of ammonia, and oxygen gases. 2Identification of the composition of some salts. SCOPE DOCUMENT Learning outcomes - Core At the end of this unit, students should be able to - 2Define acids and bases in terms of H+ and OH- 2List and explain characteristic properties of acids and bases. 2Name several common acids and bases. 2Distinguish between acids and bases and demonstrate how to test for them 2Identify and describe strong and weak acids and bases. 69

4 2Define acidity and alkalinity in terms of ph 2Understand the concept of acids and bases in our daily routine. 2Describe the role of antacids and understand neutralization using real life problems. 2Identify acidic, basic and neutral oxides. 2Explain the preparation of salts and their nature. 2Identify carbon dioxide, hydrogen and oxygen gases. 2See how acids and bases combine to produce salts Learning outcomes - Extension At the end of this unit, students should be able to- 2Understand the ph scale as it corresponds to acidic and basic solutions 2Calculate the ph of a given solution using log. 2Identify NH and Cl gases Identify the composition of salts by performing qualitative anion and cation analysis. Cross curricular links 2Biology/Life Sciences - Cell Biology 2Students know enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the ph of the surrounding, ph of the mouth, tooth decay, acidity in stomach, cure of bee and wasp sting. 2Mathematics - Calculation of ph of a given solution(extension) 2Environment - ph of the soil, acid rains due to environmental pollution, 2Music- A rap song on ph and another on properties of acids and bases 2Home Science- The salts in the kitchen and usage of the salts for various household activities. 70

5 Lesson Template Steps to be followed Warming up Activity Teacher's Activity Teacher may start by asking few brain storming questions related to daily life experiences. We have studied about nutrition in animals, recall what is secreted by the inner lining of the stomach to help in the process of digestion? Have you ever suffered from a c i d i t y i n s t o m a c h / indigestion? How do we cure it? Do you remember any advertisement or an occasion at home where acidity in stomach and its cure were discussed? Have you ever used baking soda in the kitchen? Have you eaten salads with vinegar dressings? Student's Activity Students try to think and answer by recalling the concepts learnt in biology. Students try to think and a n s w e r f r o m t h e i r experiences. Pre Content Acids and Bases Teacher asks the students as to what they understand by the terms acids and bases? Students have an idea about these terms from their lower classes, they discuss in class and also give some examples that they know. 71

6 Concept Development Content 1 Acid And Baseexperimentation and development of concept further The teacher lists the properties of acids and bases as told by the students on the board Teacher takes the students through the experience of finding the acidic or basic nature of various substances which are of daily use for example- shampoo, soap, water, tea, fruits, etc. Teacher may involve the students in the pre-lesson activity of bringing various samples from home to be tested. Activities: 1A, 1B, 1C, 1D. Following video may be shown to the students so that they have fun while learning ztlije-j1-i&feature=related Red Cabbage ph Indicator 6fc8KBz_I9s&feature=related The students will be able to- Describe acids and bases in terms of H+ and OH- Distinguish between acids and bases on the basis of their behaviour towards litmus indicator C a t e g o r i s e substances as acidic or alkaline? Worksheet:1.1 Content 2 Dissociation of acids and bases, Electrical conductivity ACTIVITY-2 Learning objectives: The students will be able to- define, dissociation, electrolyte, non-electrolyte, ph. predict if a compound is an electrolyte or a non-electrolyte. explain how an electrolytic solution c o m p l e t e s t h e c i r c u i t i n a conductivity apparatus so that the light bulb glows. Take any popular soft drink which promises to replenish your body's electrolytes when you drink it. Use the internet t o r e s e a r c h w h i c h i n g r e d i e n t ( s ) a r e contained that make this drink an electrolytic solution. Also research how the body uses 72

7 Distinguish between strong and weak acids and bases in terms of the extent of dissociation, reaction with water and electrical conductivity. electrolytes and why t h e y n e e d t o b e r e p l e n i s h e d a f t e r exercise. Worksheet-2.1 Content 3 ph of acids, bases and salts ACTIVITY-3 Learning objectives: Students Will be able to- Define acidity and alkalinity in terms of ph Understand role of ph in day to day life. Following video links on youtube may be shown in the class to sum up the concept. Hd7wRkJNgI&feature=related M8tTELZD5Ek&feature=related The ph scalevideo: M8tTELZD5Ek&feature=related Students bring various t h i n g s l i k e s o a p, detergent, moisturizing lotion, spices from the kitchen etc to test their ph. Worksheet-3.1 Content 4 Reaction of acids with metals Activity-4 Learning objectives: The students will be able to- Observe and study the reaction of acids with a metal Compare the reactivity of different metals with the same acid. Compare the reactivity of different acid with same metal. Students perform the activity and follow up witgh the worksheet. Worksheet

8 Content 5 Reaction of acids with metal oxides Activity-5 Learning objectives: The students will be able to- Appreciate that metals develop an oxide coating over a period on exposure to air Observe and study the reaction of acids with a metal oxide. Students perform collect dull coins and articles from home and bring back the shine using vinegar. They may be involved in hypothesis - whether acids or bases should be used to clean the metal surface. Worksheet-5.1 Content 6 Reaction of acids with carbonate and bicarbonates of metals. Preparation and Properties of carbon dioxide gas. ACTIVITY-6 Learning objectives: The students will be able to- Observe and study the reaction of acids with a carbonate. Observe and study the effect of carbon dioxide gas on lime water. Teacher may use the following site in the class to bring virtual kitchen experience or guide the students to perform activities at home in the real kitchen. chen/ Extension activity: Students design a soda acid fire extinguisher, b a s e d o n r e a c t i o n between sulphuric acid and sodium hydrogen carbonate students Recognise the release a n d p r o d u c t i o n o f hydrogen gas. Worksheet-6.1 Content 7 Neutralization reaction and balancing of reactions ACTIVITY-7 Learning objectives: The students will be able to- Define neutralization Identify the products of a chemical reaction between an acid and a base. Write the word equations for the observed chemical reaction Extension activity: Students design a soda acid fire extinguisher, b a s e d o n r e a c t i o n between sulphuric acid and sodium hydrogen carbonate students 74

9 Write symbols and formulae for the reactants and products Balance the chemical equation for the observed reaction. Recognise the release and production of hydrogen gas. Worksheet-6.1 Content 8 Salts Content 9 Some important salts Activity-8 Learning Objectives: The students will be able to: Recall that an acid reacts with a base to produce salt and water. Recognise the acid and base that would combine to give the given salt. Correlate the acidic, basic or neutral nature of the salt to the strength of the acid and base which may be used to obtain the salt Appreciate that all salts are not neutral. Conceptualise the formation and nature of a salt. Salts LHRek-ROQjE Teacher may start with some commonly used salts in the kitchen and hold a small discussion in the class showing the samples and some simple reactions may follow. Activity-9 Students strengthen the concept by working on the worksheet. Worksheet

10 Content 10 Qualitative Analysis of Anions and cations ACTIVITY 10 The process of identifying unknown cations or anions in a solution is called Anion and Cation analysis Students will perform qualitative analysis of salts to identify the composition of given salt. 5. Post Content Activity Revision Resource: Resource: istry/ks3.htm Resource: Y11revQs/acidreactionequationsFH.h tm Revision worksheets- 1,2,3,4 6. Extension Teacher initiates an investigation by asking a guiding question. Chemistry Investigation Guiding Question: "Which is the most effective antacid?" Students formulate hypothesis, decide on the variables and reach conclusions to be shared in groups. Peer evaluation by taking feedbacks from other groups. 76

11 Why Study about Acids, Bases and Salts? Warm up Activity Teacher may ask following questions to relate the topic to their day today life so that they realize the need to study about Acids, Bases and Salts. 2We have studied about nutrition in animals, recall what is secreted by the inner lining of the stomach to help in the process of digestion? Was it mucous, hydrochloric acid and digestive juices? 2Have we ever suffered from acidity in stomach/ indigestion? 2How do we cure it? Do we remember any advertisement or an occasion at home where acidity in stomach and its cure were discussed? 2We have carried out activities of tasting food and categorising them as sour, bitter, sweet or salty in lower classes. How are these chemically same or different? 2What makes the cake fluffy or the pakoras crispy? 2Why are farmers advised to get their soil tested before selecting and putting fertilisers? 2Why are we coaxed to brush and rinse our mouth after eating? 2Why people rub an iron key or baking soda as a home remedy for relief from itching caused due to bee or red ant sting? 2Can you think of some more examples from everyday life? To know answers to these we'll have to study about acids, bases and salts. We come in contact with them when cooking, cleaning and eating. 77

12 ACIDS, BASES AND SALTS ACTIVITY-1 Learning objectives: The students will be able to- 2Distinguish between acids and bases on the basis of their behaviour towards litmus indicator 2Distinguish between acids and bases on the basis of their behaviour towards home made indicators-turmeric, red cabbage etc. 2Describe acids and bases in terms of H+ and OH- ACID OR ALKALI? ACIDIC OR ALKALINE? 2According to earlier views, Acids produce solutions that: 2taste sour. 2react with metals to liberate hydrogen gas. 2turn blue litmus red. 78

13 2conduct electricity. 2are corrosive. (acid rain) 2loose the above properties when reacted with a base. Bases produce solutions that: 2taste bitter. 2turn red litmus blue. 2conduct electricity. 2feel slippery. 2are corrosive (basic solution in glass container) 2lose the above properties when reacted with an acid. Acid Household Source Base Household Source citric acid oranges, grapefruits sodium hydroxide oven cleaner (caustic soda) tartaric acid Grapes magnesium milk of magnesia hydroxide ascorbic acid acetic acid methanoic acid butanoic acid oxalic acid stearic acid Vitamin C Vinegar stingers of some ants rancid butter Tomatoes animal fat According to one of the modern theories of acids and bases (Arrhenius concept), An acid is a substance which give hydrogen ions in aqueous solution for e.g. HCl (Hydrochloric acid), H SO (Sulphuric acid) etc. Substances like C H OH (ethyl alcohol), C H 2O (glucose) etc though contain hydrogen are not acidic as they do not produce hydrogen ion when dissolved in water. 79

14 Base is a substance which give hydroxyl ions in aqueous solution For e.g. NaOH (sodium hydroxide), NH OH (ammonium hydroxide) etc are bases. Substances like C H OH (ethyl alcohol) contains -OH group but it does not ionize in the aqueous solution to give OH- ions. Hence, it is not a base. NOTE- The bases which are soluble in water are called alkalies. Thus all alkalies are bases but all bases are not alkalies. 80

15 TESTS TO DISTINGUISH BETWEEN ACIDS AND BASES Indicators are chemicals that indicate whether a substance is an acid or a base We use acidbase indicators to distinguish between acids and bases. Depending upon the property of the indicator we have the following two types of acid base indicators: A. Indicators showing different colours in acidic and basic medium 2Litmus solution- Litmus solution is a purple coloured dye extracted from lichen plant. It is the most commonly used natural indicator. Two types of litmus solutions are used called blue litmus solution and red litmus solution. An acid turns blue litmus solution to red colour and a base turns red litmus solution to blue colour. 2If the blue litmus paper turns red or the red litmus paper is unaffected then the substance is acidic. 2If the red litmus paper turns blue or the blue litmus paper is unaffected then the substance is alkaline. 2If neither red nor the blue paper changes colour, the substance is neutral. Note- Turmeric is a natural indicator which is yellow in colour. It becomes reddish brown when soap, which is basic in nature is scrubbed on it. 2Synthetic Indicators- The two most commonly used synthetic acid-base indicators are phenolphthalein and methyl orange. Their colours in acidic and basic solutions are- Indicators Colour in acidic solution Colour in basic solution Phenolphthalein Colourless Pink Methyl orange Pink Yellow B. Indicators giving different odours in acidic and basic medium (Olfactory indicators)-there are some substances which give one type of odour in acidic medium and a different odour in the basic medium. Vanilla essence, clove oil and onion odoured cloth strip are some of the olfactory indicators used. 81

16 Type of Activity: Warm up Activity-1A Aim: To test a variety of substances to see if they are acidic or alkaline using litmus paper as an indicator. Materials Required: Red and blue litmus paper (3 strips of each) Access to small amounts of common everyday substances such as: 2fizzy drinks 2tap water 2distilled water 2toothpaste 2shampoo 2soap 2vinegar 2lemon juice 82

17 Technical notes 1. Provide small amounts of the samples on watch glasses. The watch glasses can be placed on a white tile marked with the name of the substance - use a waterproof marker. 2. The samples can be arranged around the room so that the students visit each in turn. If any solid sample is used, moisten it with a little distilled water. Procedure: 1. Tear each piece of litmus paper into 3 smaller pieces so that you can test at least 9 substances. 2. Take one small piece of red litmus paper. Dip it into one of the substances to be tested. Repeat with a small piece of the blue litmus paper. 3. Record all observations. Then dispose of the pieces of litmus paper in the waste bin. Observations: Name of substance Effect on blue Effect on red Nature litmus paper litmus paper (Acidic/Basic/ Neutral) Fizzy drinks Tap water Distilled water Toothpaste Shampoo Soap Vinegar Lemon juice 83

18 Extension Activities: The juice of the red cabbage leaf is a naturally occurring acid base indicator. Use the internet to research if there are any other naturally occurring ph indicators. If so what do they share in common with the red cabbage? What are the differences? Then collect samples of various cleaning solutions, cosmetic solutions, cough syrups, and beverages that are available in your home. Based on their functions, predict whether these solutions are acidic, basic, or neutral. Then design an experiment to verify your predictions. Be sure to include which indicator you plan to use and why you picked it. Activity-1B Turmeric as indicator Indian curries contain turmeric (haldi). The curcuma present in turmeric reacts with base to form a red coloured substance whereas it does not change colour in acidic or neutral solution. Now can you tell without tasting the nature of soap and lemon juice respectively? Yes your guess is right- soap is a basic in nature whereas lemon juice is either acidic or neutral. Aim: To test a variety of substances to see if they are acidic or alkaline using turmeric as an indicator. Materials Required: 2Beaker 2Test tubes 2Dropper Access to small amounts of common everyday substances such as: 2Lemon juice 2Orange Juice 2Vinegar 2Curd 2Tamarind 2Juice 84

19 2Soap solution 2Baking soda 2Table Salt Solution 2Sugar Solution 2Tap Water Procedure: 2Mix half a tea spoon full of turmeric in water and filter the yellow solution in a beaker 2Collect the following substances- lemon juice, orange juice, vinegar, curd, tamarind juice, soap solution and baking soda 2Fill the test tubes with one third of these solutions respectively. 2Add few drops of turmeric solution with the help of a dropper and observe the change in colour of turmeric solution. Observations: S.No. Substance Effect on Turmeric Solution 1 Lemon Juice 2 Orange Juice 3 Vinegar 4 Curd 5 Tamarind Juice 6 Soap Solution 7 Baking Soda 8 Table Salt Solution 9 Sugar Solution 10 Tap Water 85

20 Activity-1C Aim: To test a variety of substances to see if they are acidic or alkaline using turmeric as an indicator. Materials Required: 2China rose flowers 2Hot water 2Test tubes Access to small amounts of common everyday substances such as: 2Lemon juice 2Orange Juice 2Vinegar 2Curd 2Tamarind 2Juice 2Soap solution 2Baking soda 2Table Salt Solution 2Sugar Solution 2Tap Water Procedure: 2Pluck few china rose flowers, remove their petals and put these in boiling water. 2Let them soak for in hot water for ten minutes. 2Filter the solution. Your china rose extract is ready. 2Note the colour of the extract. 86

21 2Keep 2mL extract in one test tube as control (do not add anything to it) so as to match and track the colour change. 2Test the rest of the solutions collected in activity-1b with the extract and record your observations in a table. Observations: S.No. Substance Effect on China Rose Extract 1 Lemon Juice 2 Orange Juice 3 Vinegar 4 Curd 5 Tamarind Juice 6 Soap Solution 7 Baking Soda 8 Table Salt Solution 9 Sugar Solution 10 Tap Water Activity-1D Phenolphthalein as Indicator Phenolphthalein is a synthetic indicator. It forms a colourless solution when dissolved in water. Colour of phenolphthalein does not change in acidic or neutral medium. When a drop of phenolphthalein is added to a base it imparts pink colour. So phenolphthalein is a base indicator. Test the solutions collected in activity 1 with phenolphthalein indicator and record your observations. 87

22 Testing with Red Cabbage Juice Prepare red cabbage or black carrot juice. (In northern regions of India people prepare a sour refreshing drink called 'kanji' using black carrot, rye seeds, water, salt to taste and chilli powder) and test various substances at home to classify them as acidic, basic or neutral. The red cabbage juice turns red with acid, and green to blue with base. The colours in base change from one shade to another in a few minutes, so you should note your observations fast Colour: acidic solution'dark Magenta or Red Add Soap Solution ' Turns bluish green Following video may be shown to the students so that they have fun while learning WORKSHEET The Invisible Ink Demonstration can be done at the end of this lesson as an evaluation of the students' learnings during the lab activity. Students will be required to explain the invisible ink demo and this will require that they apply their knowledge of indicators acids and bases. (Dip cotton swab into the vinegar & use it to write your secret message on the paper.allow about 1-2 min for the message to dry completely.read the "invisible ink" message by misting it lightly with the spray bottle filled with red cabbage juiceor any indicator) 2. Are most house cleaning substances acids or bases? Are most food product acids or bases? 3. Disappearing "blood" squirt guns and disappearing ink pens are available in toy stores. Both use indicators and acid/base. What indicators and acidic or basic solutions would give you such effects? 4. In basic medium colour of phenolphthalein is: (a) Yellow (b) Orange (c) Pink (d) Colourless 88

23 5. The acid present in sour milk is : (a) Citric acid (b) Lactic acid (c) Oxalic acid (d) Tartaric acid 6. Name the acid present in lemon juice and sting of bees. ACTIVITY-2 Learning objectives: The students will be able to- 2define dissociation, electrolyte, non-electrolyte, ph, neutralization. 2predict if a compound is an electrolyte or a non-electrolyte. 2explain how an electrolytic solution completes the circuit in a conductivity apparatus so that the light bulb glows. 2Distinguish between strong and weak acids and bases in terms of the extent of dissociation, reaction with water and electrical conductivity. Dissociation and Electrolyte It is observed that in water, acid molecules break up or dissociate into ions. + - HCl(aq) H (aq) + Cl (aq) Hydrochloric acid, thus, contains H+ ions. Solutions of all acids in water contain H+ ions. This is proved by the following experiment: Take sodium chloride in a dry test tube and add some sulphuric acid into the test tube.the following reaction takes place- NaCl + H SO NaHSO + HCl Sodium chloride Sulphuric acid Sodium bisulphate Hydrochloric acid Bring a dry blue litmus paper on the mouth of the test tube. It is observed that the litmus paper does not turn red. Now, bring a wet blue litmus paper on the mouth of the test tube. It 89

24 is observed that it turns red. The result clearly show that HCI acts as an acid only in the presence of water as moist litmus paper has water in which HCl gas is dissolved. It is only + after coming in contact with water that HCl dissociates into ions, i.e., hydrogen ions (H ) - and chloride ions (Cl ) + - HCl (g) + Water H (aq) + Cl (aq) Bases generate hydroxide (OH-) ions when dissolved in water. Bases which are soluble in water are called alkalis. + - KOH(aq) K (aq) + OH (aq) Compounds that dissolve in water and dissociate into ions can conduct electricity and are called electrolytes. Electrically neutral particles that are soluble in water, such as sugar, do not split up into ions and therefore, they do not conduct electricity ; hence are referred to as non-electrolytes. (This theory was originally proposed by Svante Arrhenius in 1887.) Solutions of acids or bases contain ions and are therefore electrolytes. A strong acid/base is an acid/base that is almost completely dissociated into ions in its aqueous solution. Such an acid/ base shows high conductivity A weak acid/base is an acid/base that is weakly dissociated ie. partially dissociated in its aqueous solution. Such an acid/ base shows low conductivity Strong acids Hydrochloric acid : HCl Weak acids Acetic acid : CH COOH 3 Nitric acid : HNO Sulphuric acid : H SO Phosphoric acid : H PO Boric acid : H BO Hydrobromic acid : HBr Carbonic acid :H CO 2 3 Strong bases Weak bases Sodium hydroxide : NaOH Magnesium hydroxide :Mg(OH) 2 Potassium hydroxide :KOH Ammonium hydroxide :NH OH 4 90

25 NOTE: Although water is not a strong conductor, tap water contains many charged particles, (eg: magnesium and calcium ions) hence it is dangerous to use electrical appliances in wet areas. Using a conductivity apparatus, ask students to explain how they might complete the circuit so that the light bulb will glow. Are there any materials that they can think of that can conduct electricity? (metals, water ) Type of activity: Content based Aim: Materials Required: 2Two nails 2Cork 2Beakers 2Source of electricity (6 Volt battery) 2appropriate volumes of the following solutions: Procedure: 1.0 M HCl 1.0 M NaOH distilled water solution of sugar and water vinegar 1. Fix two nails on a cork and placethe cork in a beaker. 2. Connect the nails to the two terminals of 6 volt battery through a bulb and switch. 3. Pour some HCl in the beaker and switch on the current 4. Observe what happens. Does the bulb glow. 5. Repeat the experiment separately with NaOH, distilled water, sugar solution and vinegar. 91

26 6. Record observations. Observations: Solution Intensity of light bulb Conducts Electricity? (very bright, bright, dim) (yes / no) HCl NaOH Distlled Water Sugar solution Vinegar Conclusion: 92

27 Extension activity: Take any popular soft drink which promises to replenish your body's electrolytes when you drink it. Use the internet to research which ingredient(s) are contained that make this drink an electrolytic solution. Also research how the body uses electrolytes and why they need to be replenished after exercise. Worksheet Why does the light bulb glow more brightly when the electrodes are immersed in solutions of HCl and NaOH then in vinegar? 2. Why is it dangerous to use electrical appliances in wet areas? ie: using a hairdryer while sitting in the bathtub! 3. Why the light bulb glowed when the electrodes were immersed in solutions HCl, NaOH and vinegar but not in sugar solution and distilled water. 4. Why does NaCl (aq) conduct electricity, but NaCl (s) does not? 5. List at least three household products that would be considered electrolytes. ACTIVITY-3 Learning Objectives: The students will be able to- 2Define acidity and alkalinity in terms of ph 2Understand role of ph in day to day life. EXPRESSING ACIDITY OR ALKALINITY OF A SOLUTION IN TERMS OF ph You can say how acidic or alkaline a solution is using a scale of numbers called the ph scale. The ph of a solution is defined as the negative logarithm of hydrogen ion concentration in moles per litre. + ph = -log [H ] 93

28 -1 For example, if a solution has H+ ion concentration =0.1 M ie. 10 moles per litre, its -3 ph =1 and if ph of a solution is 3 then concentration of H+ ions is 10 mol per litre.the values of ph normally lie between 0 and It is found that for any aqueous solution (neutral, acidic or basic), the product of H ion concentration and OH ion concentration is always constant and equal to 10 at 25 C.This is called ionic product of water(kw) + - Kw= [H ] [OH ] = Thus for a solution if H concentration is known, OH ion concentration is fixed (because their product is always constant).hence we express the acidic, basic or + neutral character of any solution by expressing its H ion concentration in terms of ph where p stands for potenz ie power. + - For neutral solutions : [H ] = [OH ], ph = For acidic solutions : [H ] > [OH ], ph < For basic solutions : [H ] < [OH ], ph > 7 ph [H ] (mol/l) ph between 0 and 2 -Strongly acidic ph between 2 and 4 -Moderately acidic ph between 4 and 6 -Weakly acidic ph 7 -Neutral ph between 7and 10 -Weakly basic ph between 10and 12 -Moderately basic ph between 12and 14 -Strongly basic 94

29 ph of any solution can be found by using universal indicator. This is a mixture of dyes and can be used as solution or paper strip. Colour change in the indicator is seen with ph. ROLE OF ph IN EVERYDAY LIFE 1. Human blood, tears and saliva have ph range of 7.0 to 7.8, If ph falls below 7 or rises above 7.8 survival of living organisms becomes difficult. 2. Human skin has a slightly acidic ph. This is necessary to keep away from attack by microorganisms. 3. Plants have a healthy growth if ph of the soil is such that it is neither alkaline nor highly acidic. 4. Hydrochloric acid produced in the stomach helps in digestion. However if excess of acid is produced due to spicy food, it causes indigestion and we have to take 'antacid' like milk of magnesia (magnesium hydroxide solution) etc. 5. Acid is produced in the mouth due to degradation of sugar and left out particles It is partially neutralized by the saliva. However, if excess acid is produced due to sweets, it causes tooth decay. 6. Animals and plants have self defence through chemical warfare. The sting by honey bee or yellow ant or leaves of nettle plant injects methanoic acid into our body which causes pain. 7. The tarnished surface of a copper vessel due to copper oxide (which is basic) layer can be cleaned by rubbing with lemon (which is acidic). Following video links on youtube may be shown in the class to sum up the concept

30 Work Sheet Give reasons for the following: a. Toothpastes are alkaline in nature b. We apply solution of mild base on bee or ant sting c. We rub lemon on tarnished copper vessels. 2. Seven solutions A, B,C, D,E, F and G have ph 1,2,7,9,11,13 and 14 respectively. a. Identify which of them is strongly acidic. b. Identify which of them is neutral. c. Identify which of them is weakly basic. d. Identify which of them is strongly basic. e. Which of them will turn phenolphthalein pink? f. Which of them will turn methyl orange pink? ACTIVITY-4 Learning objectives: The students will be able to- 2Observe and study the reaction of acids with a metal 2Compare the reactivity of different metals with the same acid. 2Compare the reactivity of different acid with same metal. REACTION OF ACIDS WITH METALS The only metals that react with acids are those that are more reactive than hydrogen.the metals give up their electrons to H+ ions will react with acid The result of the reaction are metal salts of the acid and evolution of bubbles of hydrogen gas through the solution. 96

31 Acid + Metal Salt + Hydrogen gas Zn (s) + 2H SO (aq) Zn SO (aq) + H (g) Zinc dil Sulphuric acid acid Zinc sulphate Hydrogen Mg (s) + 2H SO (aq) MgSO (aq) + H (g) Magnesium dil Sulphuric acid Magnesium sulphate Hydrogen Al (s) + 3HCl(aq) AlCl (aq) + H (g) 3 2 Aluminium dil Hydrochloric acid Aluminium chloride Hydrogen Cu (s) + 2H SO (aq) No reaction 2 4 Copper dil Sulphuric acid 2. Some bases like sodium hydroxide and potassium hydroxide react with active metals like zinc and aluminium to liberate hydrogen gas along with the formation of a salt. 2NaOH + Zn Na2ZnO2 + H2 Sodium hydroxide Zinc Sodium zinczte Hydrogen 2NaOH + 2Al + 2H2O 2NaAlO2 + 3H2 Sodium hydroxide Aluminium Sodium aluminate Hydrogen Type of Activity: Content based Aim: To test the reactivity of metals with an acid and compare their reactivity. Materials required: Part -I 2 Boiling test tubes with cork containing a dropping funnel and delivery tube 2Clamp stand 2Dilute sulphuric acid 2Dilute NaOH 2Granulated zinc 2Soap solution 2A candle. 97

32 Part-II Part-III Part-I 2Four boiling test tubes with cork containing a dropping funnel and delivery tube 2Four clamp stand 2Four empty syringes 2Dilute sulphuric acid (1 M) 2Zinc granules 2Magnesium ribbon 2Copper turnings 2Aluminium strips 2Boiling test tubes with cork containing a dropping funnel and delivery tube 2Clamp stand 2Dilute sulphuric acid 2Acetic acid 2Granulated zinc Procedure: 1. Take one or two zinc granules in two test tube and close the test tubes with the cork containing a dropping funnel and delivery tube. 2. Clamp it to the clamp stand. 3. Pour about 3 ml of dilute H SO in one of the test tube and NaOH in the other test tube 2 4 through the thistle funnel. (Take care that end of the thistle funnel is dipped in dilute H SO solution.) Observe the reactions taking place. 98

33 5. Pass the gas being evolved through the soap solution. 6. Observe what happens to the soap solution. Record the in the observation table. 4. Bring a lighted candle near a gas filled bubble. Record the observation. Part-II 1. Take zinc,magnesium, aluminium and copper in four different test tubes. close the test tubes with the cork containing a dropping funnel and delivery tube. 2. Clamp it to the clamp stand. 3. Connect the delivery tube to the mouth of the syringe. 4. Pour about 3 ml of dilute H SO in the test tube through the thistle funnel. (Take care 2 4 that end of the thistle funnel is dipped in dilute H SO solution.) Measure the distance travelled by the piston of syringe after 5 minutes and record your observations. 6. Based on above observation compare the relative reactivity of metals taken. 99

34 Part-III 1. Take zinc granules in two different test tubes. close the test tubes with the cork containing a dropping funnel and delivery tube. 2. Clamp it to the clamp stand. 3. Connect the delivery tube to the mouth of the syringe. 4. Pour about 3 ml of dilute H SO in one test tube and 3mL of acetic acid in the other test 2 4 tube through the thistle funnel. (Take care that end of the thistle funnel is dipped in dilute H SO solution.) Measure the distance travelled by the piston of syringe after 5 minutes and record your observations. 6. Based on above observation compare the relative strength of the two acids taken. Observations: Part-I- Reaction of an acid with a metal 1. Effect on soap solution: 2. Effect on the burning candle: Reaction of a base with a metal 1. Effect on soap solution: 100

35 2. Effect on the burning candle: Part-II- Reaction of an acid with different metals` Metal Rate of Reaction Gas Produced Distance of piston (Fast / Moderate / (yes/no) from the mouth Slow / No Reaction) Zinc Magnesium Alumnium Copper Part-III-Reaction of zinc metal with two different acids Acid Rate of Reaction Gas Produced Distance of piston (Fast / Moderate / (yes/no) from the mouth Slow / No Reaction) Dilute H SO 2 4 Acetic acid Conclusion Part-I

36 Part-II Part-III 1. Acids react with metals to form and 2. Complete the following reactions: a. Mg + HCl b. Ca + HNO 3 c. Cu + H PO 3 4 WORKSHEET Classify the type of chemical reaction that occurred when the zinc reacted with an acid. 4. Why did some of the reactions happen at a faster rate than others (*Hint* compare each acid used, what is different about the acids that were involved in the faster reactions?) 5. Explain why it is a hazard to store acids in some metal containers, and not others. 6. When sugar is placed in water, it disappears and is said to have dissolved. When magnesium metal is placed in a solution of hydrochloric acid, it also disappears. Explain why the magnesium did not dissolve. 7. An advertisement for a trivia game features the following question "Do pearls melt in vinegar?" the "correct" answer given is "yes." Write a letter to the trivia company explaining why this is not the case. Use the internet to research the chemical composition of a pearl. Include a simplified chemical reaction demonstrating what is really happening with the pearl and vinegar. 102

37 ACTIVITY-5 Learning objective The students will be able to- 2Appreciate that metals develop an oxide coating over a period on exposure to air 2Observe and study the reaction of acids with a metal oxide. Reaction of Acids with Metal oxides Acids react with certain metals oxides to give metal salt and water. Most of these oxides are of electropositive metals. Some of the oxides are amphoteric in nature. Na O + 2HCl 2NaCl + H O 2 2 Mgo + 2HCl MgCl + H O 2 2 Al O + 6HCl Type of Activity: Content based 2AlCl + 3H O Certain metals, like copper metal, develop a greenish coating of copper oxide, on reaction with air. Acids, like acetic acids, react with the oxide to effectively remove the coating. Salts serve as a catalyst, essentially speeding up the chemical reaction. If you'd like to see what the difference would be, this is easy to do. Aim: To detect and study the reaction of acid with metal oxide Materials required: 210 dull copper coins 2100 ml vinegar 21 teaspoon salt (NaCl) 2water 2measuring spoons 2paper towel 103

38 Procedure 1. In a beaker, marked A, take salt and 50ml vinegar. 2. Stir until the salt dissolves. 3. Dip 5 coins into the solution and hold it there for seconds. Remove the coins and observe for any change. 4. Pour 50ml vinegar only in another beaker, marked B. 5. Dip 5 coins into the vinegar and hold it there. Measure the time it takes for the coins to lose the clouded appearance. Check every 60 seconds. 6. Drop the rest of the coins into beaker A. Observe the duration of cleaning action. 7. Take out the coins from the beaker with a spoon and rinse it with water. 8. Set it on a paper towel to dry. Observation: 1. Observe the coins for regaining the shiny appearance, on the action of vinegarof the side of the test tube on pouring acid: 2. Which beaker showed the cleaning action faster beaker A or beaker B Conclusion: WORKSHEET Acids react with metal oxides to form and. 2. Complete the following reactions: a. HCl + CuO 104

39 b. HCl + MgO c. HNO3 + Na2O 3. Explain, with the help of a chemical equation, the role of salt in this activity. 4. Why don't we use a base or soap to clean the metal surface? ACTIVITY-6 Learning objectives: The students will be able to- 2Observe and study the reaction of acids with a carbonate. 2Observe and study the effect of carbon dioxide gas on lime water. REACTION OF ACIDS WITH CARBONATES 1. Acids react with metal carbonates and bicarbonates to give out carbon dioxide with effervescence and forming the corresponding salt and water. Metal carbonates/metal hydrogencarbonate + Acid Salt + Carbon dioxide + Water Na CO (s) + 2HCl (aq) 2NaCl(aq) + H O(l) + CO (g) Sodium carbonate Hydrochloric acid Sodium chloride Water Carbon dioxide NaHCO (s) + HCl(aq) NaCl(aq) + H O(l) + CO (g) Sodium bicarbonate Hydrochloric acid Sodium chloride Water Carbon dioxide On passing the carbon dioxide gas evolved through lime water,lime water turns milky due to the formation of insoluble calcium carbonate. Ca(OH) (aq) + CO (g) CaCO (s) + H O(l) Lime water Carbon dioxide Insoluble calcium Water carbonate On passing excess of carbon dioxide the lime water turns transparent due to formation of soluble calcium bicarbonate. Ca(OH) (aq) + CO (g) Ca(HCO ) (aq) Lime water Carbon dioxide Soluble calcium bicarbonate 105

40 Type of Activity: Content based Aim: To test the reactivity of acids with a carbonate. Materials required: 2Boiling test tubes with cork containing a dropping funnel and delivery tube 2Clamp stand 2Dilute hydrochloric acid 2Solid sodium carbonate 2Lime water Procedure: 1. Take solid sodium carbonate in the test tube and close the test tube with the cork containing a dropping funnel and delivery tube. 2. Clamp it to the clamp stand. 3. Pour about 3 ml of dilute HCl in the test tube through the thistle funnel. (Take care that end of the thistle funnel is dipped in dilute HCl solution.) 4. Observe the reaction taking place. Record the observation. 5. Pass the gas evolved through the lime water taken in a test tube. 6. Observe what happens to the lime water. Record the observation. 7. Pass the gas evolved in the lime water for longer time and observe what happens? Record the observation. 106

41 Observation: 1. Observations of the side of the test tube on pouring acid: 2. Observations in lime water after passing the evolved gas: (a) (b) immediately after passing gas: after one minute: Conclusion: NOTE: The above experiment can be repeated by taking 1-2 g of sodium hydrogen carbonate in place of sodium carbonate. Extension activity: Based on reaction between sulphuric acid and sodium hydrogen carbonate students may be asked to design a soda acid fire extinguisher. 5. Acids react with carbonates to form, and 6. Complete the following reactions: a. HCl + Na2CO3 b. HCl + KHCO3 c. HNO3 + NaHCO3 WORKSHEET Explain with the help of chemical equation for the reaction occurring in fire extinguisher. 107

42 ACTIVITY-7 Learning objectives: The students will be able to- 2Identify the products of a chemical reaction between an acid and a base. 2Write the word equations for the observed chemical reaction 2Write symbols and formulae for the reactants and products 2Balance the chemical equation for the observed reaction. 2Derive a general equation for neutralization reactions. 2Understand and appreciate the function of an indicator to indicate completion of a neutralization reaction. Neutralisation + - Acids release H into solution and bases release OH. If we were to mix an acid and base + - together, the H ion would combine with the OH ion to make the molecule H2O, or plain water: + - H (aq) + OH (aq) H O 2 108

43 This reaction called neutralization reaction of an acid with a base will always produce water and a salt, as shown below: Acid Base Water Salt HCl + NaOH H O + NaCl 2 HBr + KOH H O + KBr 2 Type of activity: Content based Aim: To observe the reaction of acid with base using different strengths/concentrations of base Materials required: Part-I 2Test tubes 2Dilute NaOH solution 2Dilute HCl solution 2Phenophthalein solution Procedure: 1. Take about 2 ml of dilute NaOH solution in a test tube and add two drops of phenophthalein solution. 2. Observe the colour of the solution. 3. Add dilute HCl solution to the above solution drop by drop until the pink colour of reaction mixture is discharged. 4. Now add a few drops of NaOH to the above mixture. 5. Observe the change in colour of the reaction mixture. 6. Why do you think this has happened? 109

44 Part-II The above activity may be performed in the form of a demonstration with the following suggested variations. Students may be involved in the demonstration. 1. The teacher may also bring about the concept of concentration of an acid by carrying out the activity in four test tubes marked A,B,C and D containing varying strengths/ concentrations of base ( NaOH). 2. The ph of all the four NaOH solutions should be found with the help of universal indicator and recorded by the students. In the table provided. 3. The concentration of the acid used for neutralization is to be kept constant (HCl). The ph of acid may be found and recorded. 4. The teacher may again reiterate the choice, use and need of indicator in this activity. 5. Let the students count the number of drops of acid required to change the colour of the solution and neutralize the base. Observations: Part-I Part-II Test ph of the base Colour shown by Number of drops of acid tube no. phenolphthalein required for complete indicator neutralization A B C D ph of acid= 110

45 Conclusion: Suggestive remediation: 2The above activity if performed with patience involving the students will prove an excellent tool for removing misconceptions about strength and concentration of an acid and base. The same activity may then be performed by choosing a weak base sodium bicarbonate and strong acid HCl or a weak acid oxalic acid and strong base NaOH. 2Some students may find it difficult to write the chemical reaction involved and a generalized chemical equation. Such students may be encouraged to memorise the symbols and valencies from Table 3.6 on page 37 of Class IX, NCERT science textbook and revise writing and balancing of chemical equations. 2Some students may find it difficult to differentiate between the terms - a strong acid/ base and a concentrated acid/ base. They may use the two terms inter changeably, through this activity teacher may clarify this doubt. 2Extra caution may be taken in explaining precautions to the students. 2Attention of the students should be drawn towards how to add the acid slowly with the help of a dropper without spilling any acid. 2Development of observation skills in learners is an important expectation from teaching/ learning of science. Special focus and attention may be given to this aspect. 2As this activity involves working with acid and base, the concentration of the acids should not be more than 0.01M or even more dilute. 2Approximately diluting 1mL of commercially available concentrated acid to 1L aqueous solution. Note: For dilution, add acid to a large volume of water and not the other way round 111

46 20.4g of NaOH pellets may be dissolved in water to make a solution of 1L to get a 0.01M NaOH solution. Same NaOH solution may be diluted further in presence of students to get solutions of varying concentrations. Worksheet-7.1 Answer the following questions one by one as the chemical reaction demonstrated in the class is taken forward: Q1. Write the names of the reactants taking part in the chemical reaction during the demonstration Q2. List the observation (s) which justify that a chemical reaction has taken place. Q3. Write a word equation and a balanced chemical equation for the complete chemical reaction that has taken place. Q4. Write a generalized equation for a neutralization reaction. Q5. Which of the four test tubes contains higher concentration of the base? Q6. Does ph of a solution change with dilution?. Worksheet-7.2 Q Write balanced chemical equations for the following word equations: a) Reaction of acid with metal Calcium + Hydrochloric acid Calcium chloride + Water General equation: Balanced equation: b) Reaction of base with metal Zinc + sodium hydroxide sodium zincate + Water General equation: Balanced equation: 112

47 c) Reaction of acid with metal carbonate Calcium carbonate + Hydrochloric acid Calcium chloride + carbon dioxide +Water General equation: Balanced equation: d) Reaction of acid with metal hydrogen carbonate Sodium hydrogen carbonate + hydrochloric acid sodium chloride + carbon dioxide +Water General equation: Balanced equation: e) Reaction of acid with metallic oxides Magnesium oxide + Hydrochloric acid magnesium chloride + Water General equation: Balanced equation: Suggestive Remediation 2Students must be encouraged to recall and memorise the valency and symbol table 3.6, given in class IX, NCERT science textbook on page 37 so that they may be able to write the formulae of any given inorganic compound by just crisscross of valencies and do not take to rote memorization of each formula. 2Initially some students may find it difficult to generalize the reactions, encourage them by writing more reactions of similar reactants on the board. 2While carrying out the above worksheet, the teacher may also draw the attention of the students towards categorizing the reactions into different types studied in the previous unit of 'Chemical Equations and Reactions'. 2An extension to the above worksheet may be designed by the teacher by asking students to formulate their own reactions by taking reactants of their choice. 2Another extension to the same may be done in the form of a game where students of one team write reactants on the board and the members of the other team suggest the products. All this will surely take the students away from rote memorization of the reactions and will lead to appreciation of the chemical reactions. 113

48 Activity-8 Learning Objectives: The students will be able to: SALTS 2Recall that an acid reacts with a base to produce salt and water. 2Recognise the acid and base that would combine to give the given salt. 2Correlate the acidic, basic or neutral nature of the salt to the strength of the acid and base which may be used to obtain the salt 2Appreciate that all salts are not neutral. 2Conceptualise the formation and nature of a salt. A salt is a compound formed by replacement of either all or a part of the ionisable hydrogen atoms of an acid by some other cation Acid + Base Salt + Water TYPES OF SALTS 1. Normal salts-.salts formed by complete replacement of all the ionisable hydrogen atoms of an acid by metallic or ammonium ions. For eg.nacl, KNO, 3 Na CO, Na SO etc Acid salts-salts formed by partial replacement of ionisable hydrogen atoms of an acid by metallic or ammonium ions. For eg. NaHCO, NaHSO, KH PO, K HPO etc Basic salts-salt formed by partial replacement of hydroxyl groups of a base by some other anion. For eg. Basic lead chloride Pb(OH)Cl, basic magnesium bromide Mg(OH)Br etc. Type of activity: Content based Task: Individual Worksheet 114

49 Procedure: The students may be given the following worksheet of completing the table after the teaching-learning of reaction between acid and base to form salt to strengthen the concept. This worksheet may be used to introduce concept of 'salts' in the class. Assessment Parameters: Each of the following questions may be assessed giving equal weightage of 2 marks to each salt. Marks may be converted to grades on a 10 point grade system. Student Worksheet: Time: 30 minutes Q Complete the following table: Salt Acid used Strong Base used Strong/ Predicted nature /weak (S/W) weak (S/W) of the salt- acidic, basic or neutral Sodium chloride Potassium nitrate Zinc sulphate Sodium acetate Potassium carbonate Copper chloride Aluminium chloride Sodium hydrogen carbonate Ammonium chloride Potassium sulphate 115

50 Suggestive Remediation 2Students must be encouraged to recall and memorise the valancy and symbol table 3.6, given in class IX, NCERT science textbook on page 37 so that they may be able to write the formulae of any given inorganic compound by just crisscross of valencies and do not take to rote memorization of each formula. 2Initially some students may find it difficult to identify the acid and base used to make the salt, encourage them by telling them to write reactions of formation of salts. 2Students may be told that a salt of a- strong acid + strong base = neutral weak acid + strong base = basic strong acid + weak base = acidic weak acid + weak base = may be neutral, acidic or basic 2While carrying out the above worksheet, the teacher may also draw the attention of the students towards acid, base indicators. 2The predictions made by the students may be checked with the help of litmus paper or solution so as to strengthen their understanding. 2An extension to the above worksheet may be designed by the teacher by asking students to formulate their own salts by taking acids and bases of their choice. 2A list of acids and bases with categories as strong and weak may be given to the students a day in advance before administering this worksheet. A list is given below to help. 116

51 Acids Hydrochloric acid Sulphuric acid Nitric acid Phosphoric acid Acetic acid Oxalic acid Strong/ weak Strong Strong Strong Weak Weak Weak Carbonic acid Bases Sodium hydroxide Potassium hydroxide Ammonium hydroxide Aluminium hydroxide Copper hydroxide Zinc hydroxide Strong/ weak Strong Strong Weak Weak Weak Weak 2Another extension to the same may be done in the form of a game where students of one team write name of a salt on the board and the members of the other team write its formula and suggest the acid, base that may be used to form that salt and predict the nature of the salt. All this will surely take the students away from rote memorization of the concept. 117

52 ACTIVITY-9 Some commonly used salts and their uses COMMON SALT- NaCl- SODIUM CHLORIDE 1. Occurrence and extraction of common salt -The important sources of common salt are- Sea water- It is one of the main source of common salt. The sea water is allowed to evaporate in shallow tanks under the influence of sun and wind. The salt obtained contains impurities which are removed by suitable methods. Rock salt- It is also found in the form of solid deposits in several parts of the world. Due to presence of impurities it is often brown in colour and is called rock salt. Rock salt is mined just like any other mineral. Inland lakes- Large quantities of salts are obtained by the natural evaporation of the water of inland lakes eg. Sambhar lake in Rajasthan(India), Great salt lake (USA) etc. 2. Uses- 2It is an essential constituent of our diet. 2It is used as a preservative for a number of food materials eg. In packed meat and fish. 2It is used for melting of ice on icy roads. 2Mixed with ice it is used as freezing mixture eg. In making of icecreams. 2It is an important starting material for the production of number of other chemicals such as sodium, chlorine, hydrochloric acid, sodium hydroxide, caustic soda(naoh), washing soda, baking soda etc. CAUSTIC SODA-NaOH-SODIUM HYDROXIDE 1. Manufacture / Preparation- It is prepared by passing electricity through an aqueous solution of sodium chloride (called brine) in a specially designed cell. As a result of electrolysis chlorine gas is given off at anode and hydrogen gas at the cathode. Sodium hydroxide solution is formed near cathode.this method is called Chloro-alkali process because the products are chlorine and an alkali. 118

53 electricity 2NaCl(g) + 2H O(l) 2NaOH(aq) + Cl2(g) + H2(g) 2 At anode : Cl Cl 2 + 2e At cathode : H + 2e H 2 3. Uses of Hydrogen- 2In the manufacture of ammonia which is further used for the production of various fertilizers. 2In the hydrogenation of vegetable oils to form solid fats 2In metallurgy to reduce heavy metal oxides to metals. 2Liquid hydrogen is used as a rocket fuel. 2Uses of Chlorine- 2As a germicide and disinfectant for sterilization of water in the swimming pools. 2In the manufacture of bleaching powder, chloroform, hydrochloric acid, etc. 2In the manufacture of chlorofluorocarbon compounds used as refrigerants. 2In the bleaching of wood pulp and cotton fabrics. 2In the manufacture of PVC (poly vinyl chloride) 2In the manufacture of pesticides. 4. Uses of Hydrochloric acid- 2As a reagent in the laboratory. 2In making aqua regia for dissolving gold and platinum. 2For cleaning steel. 119

54 2In textile industry. 2In the manufacture of medicines and cosmetics. 5. Uses of Caustic Soda- 2In the manufacture of soaps and detergents. 2For degreasing metals. 2In the paper industry. 2In making of artificial fibres like rayon etc. 2In the manufacture of dyes. 2In petroleum refining. 2For mercerizing cotton, i.e. making cotton unshrinkable. 2As a laboratory reagent. BLEACHING POWDER-CaOCl -CALCIUM OXYCHLORIDE 2 1. Manufacture / Preparation- It is prepared on industrial scale by passing chlorine gas through dry slaked lime. The plant generally used for the manufacture of bleaching powder is known as 'Hasenclever plant Ca(OH) + Cl CaOCl + H O Slaked lime Chlorine Bleaching powder Water 2. Properties- 2Bleaching powder is a yellowish white powder which gives strong smell of chlorine. 2It is soluble in water leaving behind a small residue of lime. 2When bleaching powder is exposed to air, it reacts with atmospheric carbon dioxide, giving off chlorine. To avoid decomposition it is packed in air tight containers. CaOCl + CO CaCO + Cl

55 2When bleaching powder is treated with excess dilute acid, chlorine gas is produced. 3. Uses- CaOCl + H SO CaSO + H O + Cl Chlorine gas produced in this way is known as 'available chlorine'. It is this available chlorine which is responsible for the bleaching action of the bleaching powder. 2Bleaching powder is chiefly used for bleaching cotton and linen textiles, wood and paper pulp. 2It is strong disinfectant and is therefore, used for sterilization of water. 2It is employed for making wool unshrinkable. 2It is also used as an oxidizing agent in the manufacture of many chemicals. BAKING SODA-NaHCO -SODIUM HYDROGENCARBONATE 3 1. Manufacture / Preparation- Baking soda is obtained as primary product in Solvay's process for the manufacture of sodium carbonate. In this process carbon dioxide gas is bubbled through saturated ammonical brine solution which results in the formation of baking soda. NaCl + H O + NH + CO NH Cl + NaHCO Ammonium Chloride Sodium bicarbonate Sodium hydrogencarbonate is sparingly soluble in water whereas ammonium chloride is highly soluble. Hence, sodium hydrogencarbonate separates out as solid. On small scale, it can be prepared in the laboratory by passing carbon dioxide gas through aqueous sodium carbonate solution. Na CO + H O + CO NaHCO Sodium bicarbonate 121

56 2. Properties- 2It is white crystalline solid. 2It is sparingly soluble in water. The solution is alkaline in nature due to salt hydrolysis. NaHCO + H O NaOH + H2CO Baking soda Sodium hydroxide Carbonic acid (Strong base) (Weak acid) 2Baking soda on heating decomposes to give carbon dioxide. Heat 2NaHCO Na CO + H O + CO It reacts with acids to liberate carbon dioxide gas with brisk effervescence. 3. Uses- 2NaHCO + H2SO Na SO + 2H O + 2CO It is used as an ingredient in antacids. Being alkaline it neutralizes excess acid in the stomach. 2It is It is used as a component of baking powder (sodium hydrogencarbonate + mild edible acid such as tartaric acid,citric acids etc.)when mixed with water and heated, baking soda decomposes producing carbon dioxide which causes bread or cake to swell and become light. Tartaric acid present in baking powder neutralizes bitter taste of sodium carbonate. 2It is used in soda-acid fire extinguishers. Soda acid fire extinguishers contain a solution of hydrogen carbonate and sulphuric acid. These two chemicals are brought in contact by pressing a knob or by inverting the extinguisher. Carbon dioxide is produced which forces a stream of effervescing liquid on the fire. CO2 surrounds the combustible substance and cuts off the supply of air. Thus the fire get extinguished. 122

57 WASHING SODA-Na CO.10H O-SODIUM CARBONATE DECAHYDRATE Manufacture / Preparation- Washing soda is prepared by Solvay's process. In this process carbon dioxide gas is bubbled through saturated ammonical brine solution which results in the formation of sodium hydrogencarbonate. NaCl + H O + NH + CO NH Cl + NaHCO Ammonium Chloride Sodium bicarbonate The sodium hydrogen carbonate is filtered off and then ignited to get sodium carbonate. Heat 2NaHCO Na CO + H O + CO Anhydrous Sodium Carbonate (soda ash) The anhydrous sodium carbonate is dissolved in water and then subjected to recrystallisation to obtain crystals of washing soda. Na CO + 10H O Na CO 10 H O Properties- 2It is transparent crystalline solid. Washing soda (Hydrous salt) 2It is readily soluble in water and its aqueous solution is alkaline in nature due to hydrolysis. Na CO + 2H O 2NaOH + H2CO Sodium Carbonate Sodium hydroxide Carbonic acid (Strong base) (Weak acid) 2When kept open in the air, the crystals of washing soda lose nine molecules of water of crystallization to form a monohydrate which is white powder. Na CO 10 H O(s) Na CO.H O(s) + 9H O(g) Transparent crystals White powder The loss of water by a crystalline solid to the atmosphere on exposure to air is called efflorescence. 123

58 2On heating washing soda loses all the molecules of water of crystallization and becomes anhydrous. Heat Na CO 10 H O(s) Na CO (s) + 10H O(g) Washing soda Anhydrous Sodium Carbonate (soda ash) 2It reacts with acid to give out CO gas with brisk effervescence. 2 Na2CO + H SO Na SO + H O + CO Sodium sulphate 2Washing soda reacts with soluble salts of calcium and magnesium present in hard water to form insoluble salts of calcium and magnesium which can be filtered off, Hence water becomes soft. Na2CO3 + CaCl2 CaCO3 + 2NaCl Calcium chloride Calcium carbonate Present in hard water Precipitate 3. Uses- 2It is used in the laundry for cleaning clothes. 2It is used in the manufacture of glass, borax, soap and caustic soda. 2It is used in paper, paints and textile industries. 2It is used for softening of hard water. It removes temporary as well as permanent hardness. 2It is used as an important laboratory reagent both in quantitative and qualitative analysis. NOTE-Water of crystallization is definite number of water molecules which are present in loose chemical combination with one formula unit of the ionic solid in crystalline form for eg. CuSO4.5H2O has 5 molecules of water of crystallization. 124

59 PLASTER OF PARIS-CaSO.1/2 H O-CALCIUM SULPHATE HEMIHYDRATE Manufacture / Preparation- It is prepared by heating gypsum to 393 K 393K CaSO..2 H O CaSO.1/2 H O + 11/2 H O Gypsum Plaster of paris The temperature should not be allowed to rise above 393K because above this temperature, the whole water of crystallization is lost resuling into formation of anhydrous calcium sulphate (dead burnt plaster). Above 393K CaSO..2 H O CaSO. + 2 H O Gypsum Dead burnt plaster 2. Properties- 2It is a white powder. 2When mixed with water and left for half an hour, it sets to hard mass. This is due to rehydration of Plaster of paris to Gypsum 3. Uses- CaSO.1/2 H2O + 11/2 H O CaSO.2 H O Plaster of paris Gypsum 2It is used for setting fractured bones in the right position and in making casts in dentistry. 2In making toys, casts for statues, decorative materials, jewellery and cosmetics. 2In making the surface smooth, e.g. that of walls, ceiling etc, before paint. 2In making chalks for writing on the black board. 2In laboratory, for making the apparatus air tight by sealing the gaps at the stopper etc. 2In making fire proof materials 125

60 PREPARATION OF ZINC SULPHATE Zinc sulphate can be made by reacting dilute sulphuric acid with zinc granules. Zn(s) + H SO (aq) ZnSO (aq) + H (g) Zinc Sulphuric Acid Zinc sulphate Hydrogen The steps involved are: a) Add excess zinc granules to the acid in a beaker, when zinc starts to dissolve and hydrogen bubbles off. Wait till effervescence is over which indicates that all the acid is used up. b) Remove excess zinc by filtration. c) Transfer the clear aqueous solution of zinc sulphate in an china dish. Heat the solution to evaporate some water. Allow to cool, when colorless crystals of zinc sulphate begin to appear. Zinc sulphate solution Dilute sulphuric acid Zinc (a) (b) (c) (a) Dissolving zinc in dilute sulphuric acid (b) Filtration of zinc sulphate solution (c) Evaporation of the zinc sulphate solution This method Is good for preparation of salts of Al, Fe, Mg. However, Cu, Ag, Au do not react at all. On the other hand, Na, K react very violently with acids. PREPARATION OF Copper sulphate In order to make salts of Cu, start with an insoluble base like CuO and react with acid. CuO (s) + H2SO 4 (aq) CuoSO 4 (aq) + H2O (I) Copper oxide Sulphuric acid Copper sulphate Water 126

61 Steps followed are: a) Take CuO in a beaker and add dil. Sulphuric acid. Warm the mixture when the metal oxide dissolves and the solution turns blue.add more CuO till no more dissolves. b) Remove excess solid by filtration c) Transfer the blue solution of copper sulphate in an china dish. Heat the solution to evaporate some water. Allow to cool, when blue crystals of copper sulphate begin to appear PREPARATION OF SALTS OF Na Na is too reactive for a reaction with acid. Instead we can use NaOH to make sodium salts. Sodium sulphate can be prepared by treating sodium hydroxide solution with dilute sulphuric acid. 2NaOHl(aq) Sodium hydroxide + H 2 SO 3(aq) Na 2 SO 4(aq) Sulphuric Sodium acid sulphate + 2H O(I) 2 Water As both the reactants and products are aqueous, we have to make sure that all the reactants are used up. This can be done as follows (i) (ii) Take dilute sulphuric acid in a burette. Take 20 ml of sodium hydroxide solution in a conical flask. (iii) Add a drop of phenolphthalein to the sodium hydroxide solution to turn the solution deep pink in color. (iv) Keep the conical flask beneath the nozzle of the burette, and open its tap to let the acid come down drop by drop into the conical flask.keep stirring the conical flask. (v) At a point of addition of the acid, the pink color in the conical flask suddenly turns colorless. This shows that all the alkali has been used up. Close the tap. (vi) Transfer the solution into an evaporating dish and carefully evaporate to dryness. (vii) Colorless crystals of sodium sulphate appear. 127

62 PREPARATION OF INSOLUBLE SALTS Salts that are soluble have been prepared by evaporation. Not all salts are soluble. Soluble Salts Insoluble salts All sodium, potassium and ammonium salts All nitrates Most Chlorides Some sulphates Sodium, potassium, ammonium Carbonates silver and lead chloride Barium, calcium and lead sulphate All carbonates Insoluble salts are prepared by precipitation Calcium Carbonate (i) (ii) Take calcium chloride in a beaker and dissolve it in water. In another beaker dissolve sodium carbonate in water. (iii) Add the sodium carbonate solution into calcium chloride solution and stir well. Reaction occurs and a white precipitate is formed. CaCl (aq) 2 Calcium chloride + Na 2 CO 3(aq) 2NaCl(aq) Sodium Sodium carbonate chloride + CaCO (s) 3 Calcium carbonate 128

63 (iv) The white precipitate formed is of calcium carbonate. Filter the precipitate and dry it. The white powder when dried on the filter paper is calcium carbonate salt Barium Sulphate Mixing solutions of Barium chloride and sodium sulphate gives barium sulphate. Steps used are: BaCl (aq) + Na SO (aq) BaSO (s) + 2 NaCl(aq) a) Make a solution of BaSO as well as a solution of Na SO b) Mix the two solutions by slowly transferring one into the other and with constant stirring. A white precipitate of barium sulphate will form at once. c) Filter the precipitate and dry in oven. Work Sheet A white substance having a strong smell of chlorine is used to clean water storage tanks. Identify the substance. Give its chemical name and write the chemical equation for its preparation. 2. When the concentrated aqueous solution of substance X is electrolysed, then NaOH, Cl and H are produced. Name the substance X. What is the name of this process Write the Chemical formula of washing soda. What happens when the crystals of washing soda are left exposed to air? 4. What colour change would you observe on adding red litmus solution to an aqueous solution of washing soda? 5. Write an equation to show the reaction between Plaster of Paris and water. 6. What will happen if a solution of sodium hydrogen carbonate is heated? 7. A compound X is obtained by heating compound Y at 373 K. When compound X is mixed with water, crystals of Y are produced. Identify compound X and Y and give two uses of X. 129

64 8. A blue salt becomes white on heating. With the help of a reaction explain the change in colour. 9. A blue salt becomes white on heating. With the help of a reaction explain the change in colour. 10. What happens when electric current is passed through brine. 11. A compound of sodium forms a white powder. It is a constituent of baking powder and is used in some antacid preparations. When heated, X gives out a gas and steam. The gas forms a white precipate with lime water. Write the chemical formula and name of X and the chemical equation for its decomposition on heating. 12. What is bleaching powder? How is it prepared? Write chemical equation involved in the preparation of bleaching powder. Write two uses of bleaching powder. 13. Name four salts you could make by precipitation 14. Name four salts you could make by evaporation 15. Name the acid and metal used to make: a) Potassium chloride b) Magnesium nitrate 16. Give the possible starting compounds to make the following salts a) Lead chloride b) Calcium sulphate c) Magnesium carbonate d) Lead carbonate ACTIVITY 10 Qualitative Analysis of Anions and cations The process of identifying unknown cations or anions in a solution is called Anion and Cation analysis 130

65 Test for ANIONS CARBONATE Only the alkali metal and ammonium carbonates are water soluble. Dilute hydrochloric acid gives vigorous effervescence with carbonates, evolving carbon dioxide that turns lime water milky: 2- + CO 3 (aq or s) + 2H (aq) H2O(l) + CO 2(g) CO (g) + Ca(OH) CaCO (aq) +H O(l) CHLORIDE: AgCl, PbCl, Hg Cl and CuCl are insoluble in water Silver nitrate solution added to a solution of a chloride that has been acidified (test with blue litmus paper) with dilute nitric acid gives a white precipitate of silver chloride. The precipitate is readily soluble in dilute ammonia. IODIDE: Ag+(aq) + Cl-(aq) AgCl(s) + - AgCl(s) + 2NH 3(aq) [Ag(NH3) 2] (aq) + Cl (aq) Silver nitrate solution added to a solution of an iodide that has been acidified (test with blue litmus paper) with dilute nitric acid gives a yellow precipitate of silver iodide. The precipitate is insoluble even in concentrated ammonia: + - Ag (aq) + I (aq) AgI(s) SULPHATE BaSO, SrSO and PbSO are insoluble; Ca SO is sparingly soluble Barium nitrate solution added to the test solution acidified with dilute hydrochloric acid gives a white precipitate of barium sulphate: Ba +(aq) + SO4 -(aq) BaSO (s)

66 NITRATE Nitrate ions are reduced to ammonia by boiling with aluminium in sodium hydroxide solution. Warm the test solution with NaOH and test the vapour for ammonia- the gas that turns moist red litmus paper blue indicating nitrate in the original solution: 3NO (aq) + 8Al(s) + 18H O(l) + 21 OH (aq) CATIONS 3+ Aluminium, Al 8[Al(OH) ] (aq) + 3NH (g) Sodium hydroxide solution precipitates white gelatinous aluminium hydroxide. This reacts with excess NaOH to give a colourless solution of sodium aluminate: 3+ - Al (aq) + 3OH (aq) Al(OH) 3(s) - 3- Al(OH) 3(s) + 3OH (aq) [Al(OH) 6] (aq) Ammonia solution precipitates white aluminium hydroxide, as with NaOH; however it does not react further with excess ammonia. + NH 4 Alkalis (sodium hydroxide, calcium hydroxide) liberate ammonia from ammonium salts on warming with the solution, or even from a mixture of the solids. + - NH 4 (aq) + OH (aq) NH 3(g) + H2O(l) The test solution is warmed with sodium hydroxide solution and the vapours tested with moist red litmus paper. It is important to test the vapours immediately heating begins, since the ammonia is lost very quickly and by the time the solution boils it may well have all gone. Calcium,Ca2+ Sodium hydroxide solution gives white ppt that remains insoluble. - Ca 2+(aq) + OH (aq) Ca(OH) 2(s) With ammonia, little or no reaction occurs. 132

67 Copper(II) Sodium hydroxide solution gives a pale blue precipitate usually described as copper(ii) hydroxide: 2+ - Cu (aq) + 2OH (aq) Cu(OH) (s) 2 Ammonia solution initially gives a blue precipitate as for sodium hydroxide. Further addition of ammonia gives deep blue solution. Fe(II) Sodium hydroxide solution precipitates dirty green iron(ii) hydroxide.; on standing the surface of the precipitate turns foxy-red owing to air oxidation to iron(iii) hydroxide: 2+ - Fe (aq) + 2OH (aq) Fe(OH) 2(s) Ammonia solution behaves similar to sodium hydroxide. Zinc(II) Sodium hydroxide solution precipitates white zinc(ii) hydroxide, easily soluble in excess sodium hydroxide to give sodium zincate(ii), because the hydroxide is amphoteric: - Zn 2+ (aq) + 2OH (aq) " Zn(OH) 2(s) - 2- Zn(OH) 2(s) + 2OH (aq) " Zn(OH) 4 (aq) Ammonia solution initially precipitates zinc(ii) hydroxide, as with sodium hydroxide. Excess ammonia causes the precipitate to disappear. Test for anions anion test test result 2- carbonate (CO 3 ) add dilute acid effervescene, carbon dioxide produced - chloride (Cl ) (in solution) - iodide (1 ) (in solution) - nitrate (NO 3 ) (in solution) 2- sulfate (SO 4 ) (in solution) acidify with dilute nitric acid, then add aqueous silver nitrate acidify with dilute nitric acid, then add aqueous silver nitrate add aqueous sodium hydroxide then aluminium foil, warm carefully acidify with dilute nitric acid, then aqueous barium nitrate white ppt. yellow ppt. ammonia produced white ppt. 133

68 Test for aqueous cations cation 3+ aluminium (Al ) + ammonium (NH 4 ) 2+ calcium (Ca ) 2+ copper (Cu ) 2+ iron (II) (Fe ) 3+ iron (III) (Fe ) 2+ zinc (Zn ) effect of aqueous sodium hydfroxide white ppt., soluble in excess giving a colourless solution ammonia produced on warming white ppt., insoluble in excess light blue ppt., insoluble in excess green ppt., insoluble in excess red-brown ppt., insoluble in excess white ppt., insoluble in excess giving a colourless solution effect of aqueous ammonia white ppt., insoluble in excess - no ppt., or very slight white ppt. light blue ppt., soluble in excess giving a dark blue solution green ppt., insoluble in excess red-brown ppt., insoluble in excess white ppt., soluble in excess giving a colourless solution Gas Ammonia(NH ) Carbon dioxide (CO ) Chlorine(Cl ) Hydrogen (H ) Oxygen(O ) Test and test results Turns damp red litmus paper blue Turns limewater milky Bleaches damp litmus paper 'Pops' with a lighted splint Relights glowing splint Activity You are provided with solid E. Carry out the following tests on E, recording all of your observations in the table. Conclusions must not be written in the table 134

69 tests (a) Describe the appearance of solid E. (b) Place half of solid E in a test-tube. Heat the test tube gently. Test any gas given off with damp ph indicator paper. (c) Add the rest of solid E to about 8 cm³ of distilled water in a test-tube. Cork the test-tube and shake the contents until dissolved. Divide the solution into 4 equal portions in test-tubes and carry out the following. (i) (ii) Add several drops of aqueous sodium hydroxide to the first portion of the solution and shake the test-tube. N o w a d d e x c e s s s o d i u m hydroxide to the test-tube. Repeat test (i) using aqueous ammonia solution instead of aqueous sodium hydroxide. (iii) Test the ph of the third portion of the solution with indicator paper. Now add to the solution a b o u t 1 c m ³ o f d i l u t e hydrochloric acid followed by about 1 cm³ of barium chloride solution. (iv) To the fourth portion of the solution add an equal volume of aqueous sodium hydroxide. Now add a small spatula measure of aluminium powder and warm the mixture carefully. Test any gases given off. observations... (1) (2) (3) (2) ph... (1)... (1) (2) 135

70 Table of Qualitative solubility (Solubility rules) To use table Combine Negative ion in column A with positive ion in column B, read across table to determine solubility. Example: ZnSO Find SO 4 : read across, 2 2+ Zn is not part of first group, 2therefore part of All other positive ions 2therefore soluble All negative ions are with Alkali ions ( Li, Na, K etc) Soluble + All negative ions are with Hydrogen ( H ) Soluble + All negative ions are with Ammonium ion (NH 4 ) Soluble - Nitrate NO 3 ions are with All positive ions are Soluble - Chloride, Cl Ag, Pb, Cu ----> Insoluble (have low solubility) - Iodide I All Other positive ions----> Soluble Sulfate SO 4 Ba, Sr, Pb > Insoluble All Other positive ions -----> Soluble Carbonate CO 3 Alkali Ions, H, NH 4 Soluble All Other positive ions Insoluble 136

71 Activity Using solubility rules Write out the formula for each of the following ionic compounds ant then using the table of relative solubility given above, predict the solubility of the following ionic compounds. a) Zinc chloride b) Ammonium carbonate c) Zinc(II) sulfate d) Copper (I) Iodide e) Sodium iodide f) Calcium sulfate g) Magnesium nitrate h) Potassium sulfate i) Barium chloride j) Iron (II) carbonate 136

72 Revision worksheet-1 Complete the following cross word puzzle by taking the clues given

73 Down 1. name of process of electrolysis of aqueous sodium chloride (2 words) 2. Change in colour of litmus in basic medium (3 words) 4. chemical name of washing powder (2 words) 5. medicine for acidity and indigestion. 6. common name of sodium hydrogen carbonate (2 words) 7. Change in colour of litmus in acidic medium (3 words) 8. Gas released when an active metal reacts with an acid. 9. common name of calcium sulphate hemihydrate (3 words) 12. Acids and bases react to produce water and -- Across 1. Gas released when a metal carbonate reacts with an acid (2words) 3. This indicator gives reddish pink colour in acidic solution (2 words) 10. mixture of sodium hydrogen carbonate and tartaric acid to make cakes (2 words) 11. Common name of dilute solution of acetic acid 13. This indicator gives magenta pink colour in alkaline solution 14. Acids and bases react to give reaction 15. Plaster of Paris is obtained by heating 139

74 Revision Worksheet 2 Cross-Word Puzzle-2 Complete the following crossword puzzle by taking the clues given below Across: 2 Acids on your skin! (8) 5 The ph measure? (5) 7 Plants can't grow if it is too acidic. (4) 8 If the ph is over 7. (8) 10 Colour of litmus in acid. (3) 12 You can extract these coloured materials from plants. (7,4) Down: 1 1st name of a well known strong acid, (9) 2 To test for how acidic or alkaline a solution is. (9) 3 Latin for water (3) 4 The ph number of a strong acid. (3) 5 This kind of acid dissociates completely in water. (6) 140

75 14 Some treated with weak acid, some with weak alkali, depends on the insect! (5) 17 In the list, only just acid. (4) 18 The ph of strong acids. (3) 21 This fruit has acidic juice, good to make a cool drink. (5) 22 Spilt concentrated acid is one! (6) 23 We can get natural acid from some. (5) 24 Used to neutralise stomach acid! (7) 26 The ph of a strong alkali. (4) 31 Common name for a well known weak acid used in food preparation. (7) 6 Put on soil that is too acid for healthy plant growth. (4) 8 If the universal indicator turns red it means? (6) 9 If the universal indicator turns green it means? (7) 11 A well known indicator. (9) 13 This doesn't like too much acid, but just enough for digestion! (7) 15 The colour of universal indicator in a very strong alkali. (6) 16 The ph of a neutral solution. (5) 19 is its symbol. (9) 32 1st name of a well known acid (12) 33 This type of acid won't cause harm if it spills on you! (4) 34 "My dear Watson, this perfectly describes the effect of 'prussic acid' on the victim"! (5) 35 It turns litmus blue. (6) 36 a well known strong alkali (6,9) 20 The hazard warning sign for this is a cross. (7) 25 It neutralises an alkali. (4) 27 It means very corrosive and 'soda' is an example! (7) 28 The name of the acidity and alkalinity scale. (2) 29 This chloride is 'common salt'. (6) 30 The ph of a very weakly acid solution. (3) Resource: 141

76 Revision worksheet-3 Some incomplete word equations are given to you. Complete these by filling in the blanks- 1. zinc + hydrochloric acid ===> + hydrogen 2. + sulphuric acid ===> copper(ii) sulphate + water + carbon dioxide 3. magnesium oxide + ===> magnesium nitrate + water 4. zinc + sulphuric acid ===> zinc sulphate + 5. magnesium hydroxide + hydrochloric acid ===> + water 6. + nitric acid ===> copper(ii) nitrate + water + 7. zinc carbonate + sulphuric acid ===> + + carbon dioxide 8. iron + ===> iron(ii) chloride + hydrogen 9. magnesium oxide + hydrochloric acid ===> hydrochloric acid ===> calcium chloride + water sulphuric acid ===> magnesium sulphate + hydrogen 12. magnesium + nitric acid ===> + hydrogen 13. zinc hydroxide + ===> zinc chloride + water hydrochloric acid ===> magnesium chloride + water + carbon dioxide 15. aluminium + hydrochloric acid ===> + hydrogen 16. sodium hydroxide + hydrochloric acid ===> + 142

77 17. sodium carbonate + ===> sodium sulphate + water nitric acid ===> calcium nitrate + water + carbon dioxide sulphuric acid ===> iron(ii) sulphate + hydrogen 20. zinc oxide + ===> zinc chloride + water 21. copper(ii) carbonate + sulphuric acid ===> + water + carbon dioxide 22. aluminium + ===> aluminium sulphate + hydrogen 23. calcium oxide + hydrochloric acid ===> magnesium hydroxide + ===> magnesium sulphate ammonia + sulphuric acid ===> 26. ammonia + ===> ammonium chloride 27. zinc hydroxide + sulphuric acid ===> copper(ii) oxide + hydrochloric acid ===> + water 29. sodium hydroxide + sulphuric acid ===> + water 30. sodium hydrogencarbonate + hydrochloric acid ===> ammonia + ===> ammonium nitrate 32. calcium oxide + ===> calcium chloride aluminium hydroxide + nitric acid ===> + water 34. calcium carbonate + ===>calcium ethanoate ethanoic acid + magnesium ===> + hydrogen magnesium oxide ===> magnesium ethanoate sodium hydroxide + ===> ethanoate + Resource: 143

78 Revision Work Sheet- 4 Choose the correct option for the following questions from the four choices given. Each question has only one correct answer. Q1. An element common to all acids is a) Chlorine b) Nitrogen c) Oxygen d) Hydrogen Q2. Bases on ionization release a) hydrogen ions b) sodium ions c) chloride ions d) hydroxide ions Q3. In general, salts a) are ionic compounds b) contain hydrogen ions c) contain hydroxide ions d) turn litmus red Q4. When water solutions of an acid and base are mixed a) no reaction occurs b) a new acid and a new base are formed c) a salt and water are formed d) an acid and a salt are formed Q5. When magnesium and hydrochloric acid react, they produce a) Oxygen and magnesium chloride 144

79 b) Chlorine and magnesium oxide c) Hydrogen and magnesium chloride d) Hydrogen and magnesium oxide Q6. When HCl(aq) is exactly neutralized by NaOH(aq), the hydrogen ion concentration in the resulting mixture is a) always less than the concentration of the hydroxide ions b) always greater than the concentration of the hydroxide ions c) always equal than the concentration of the hydroxide ions d) sometimes greater and sometimes less than the concentration of the hydroxide ions Q7. A common substance that contains acetic acid is a) Vinegar b) Ammonia water c) Salad oil d) Soap Q8. A base used in the manufacture of soap is a) Calcium hydroxide b) Sodium hydroxide c) Ammonium hydroxide d) Zinc hydroxide Q9. Which of the following solution will turn phenolphthalein pink? a) HCl(aq) b) CO (aq) 2 c) KOH(aq) d) CH OH(aq) 3 145

80 Q10. Fruit juices, such as orange juice, contain: a) Boric Acid b) Citric Acid c) Sulphuric Acid d) Nitric Acid Q11. When dissolved in water, salts a) Are non-electrolytes b) Have a bitter taste c) Are electrolytes d) Release hydrogen ions Q12. A base can be prepared by the reaction between a) An active non-metal and water b) A gas and water c) A sulphide and water d) An active metal and water Q13. Of the following, the property that most closely relates to acids is a) A bitter taste b) Contains the hydroxide ion c) Sour taste d) Salty taste Q14 A solution turns red litmus to blue. It's ph is likely to be: a) 2 b) 5 c) 7 d)

81 Q15. Which formula represents a base? a) KOH b) KCl c) CH OH 3 d) CH COOH 3 "Which is the most effective antacid?" Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding a concept students should develop their own questions and perform investigations. As inquiry based approach is not dealt with the grade so far, the inquiry question will be provided to the learners. The learner will be able to Conceptual understanding: [The conceptual understanding targeted is limited and extension may vary from section to section as per the need of the class.] The targeted conceptual understanding: 1. Understanding of the terms acid, base, salt and neutralization 2. Familiarity with various examples associated with the above four terms 3. Correlation of the above four terms in daily life context Experimentation and investigation (EI): 1. support hypothesis logically Extension Activity Chemistry Investigation (Content: Acids and bases) Objective: Learning outcome: 2. design an experiment in logical sequence to test the hypothesis 147

82 3. identify resources required for the experiment and use the same appropriately and judiciously 4. conduct multiple trials to test a prediction and draw conclusions about the relationships between predictions and results. 5. record data by using appropriate graphic representations (including charts, graphs, and labelled diagrams) and make inferences based on those data. 6. write instructions others can follow to carry out the procedure 7. validate the result and conclusion using existing literature 8. write a report of the investigation that includes conducting tests, collecting data, comparing with existing literatures and drawing conclusions. 9. include feedback to modify the investigation. Inquiry question: Which antacid can neutralize the stomach acid satisfactorily? Transaction: Plan 1: Brainstorming session EQ: Why do people say that they are suffering from acidity? What does that mean? What do they do to avoid acidity? Proceedings: (S) need to put their understanding (can be in the form of web) in the notebook individually and then (T) needs to ask (S) to share. The same will be put down on the blackboard. (T) will not share her understanding with the class. Plan 2: Investigation Proceedings: Various reading materials will be provided to (S) for them to have discussion in groups on the previous class questions. [Reading material: books n few authentic readings from net] Plan 3: Presentation Proceedings: Each group to present what they have understood from the previous readings and discussions. Once a group finishes they are required to present their understanding, the other groups can ask questions or add input to enrich the understanding for the class as a whole. Plan 4: Brainstorming session 148

83 EQ: Which antacid can neutralize the stomach acid satisfactorily? Proceedings: (S) will discuss what an antacid is and what is the meaning of neutralization? (S) will brainstorm on how to proceed to find the method to reach to the answer. (S) need to bring antacids from the market (one tablet each) and would proceed in the next class to practically find the answer of the EQ. Plan 5 + 6: Writing steps Proceedings: (S) will write their plan in steps for the experiment in the respective groups. (T) will observe each group and depending upon the status will support. Guidelines for (T) during guidance: 1. check weather the groups have written EI brainstorm in groups regarding the resources; (cost factor, easy accessibility, proper storage after and during use, safe ways of discarding) 3. check EI 5. Discuss various ways of doing the same. 4. Discuss EI 4. (What should be done to make our results accurate and authentic? (T) will encourage (S) to keep more than good no. of experimental set ups.) Plan 7 + 8: Performing the experiment (no. of periods will depend upon the design by each group) Proceedings: (T) will inform the expectation to all groups before they start with the experiment. (give photocopies) Expectation: All (S) need to submit a report of their investigation that must include a. hypothesis with reason b. resources used c. procedure (must also includes multiple trials also) d. regular observation (table, diagram etc. ) + representation of observation (any graphic organizer/graph) e. result f. research of existing literature (details need to be shared later) 149

84 g. comparison of result and literature to write conclusion. h. moments of joy and sorrow during the investigation (S) will perform the designed experiment. Plan : Compilation of the experiment Proceedings: (S) will compile all work as mentioned above (a-e). (T) will assist by reminding (S) about the pointers. Plan : Reading literature Proceedings: (S) will be provided with various reading materials in the class. Each group will be provided with same set. (S) need to read, identify the earlier findings and compare it with their results. (S) need to identify if there is any mismatch of literature with their results and brainstorm the reasons for so. (S) will work on point (g). Assignment: h. Write moments of joy and sorrow during the investigation. Extension: If possible (S) can be allowed to find out more on given sites in their computer period. (optional) Plan : Feedback to other groups Proceedings: (S) will be asked to share previous day's assignment with the class. Work of (S) need to be displayed group-wise. Each group will move to the other group's work and will look at the same and will complete the feedback form for that group. 15 mins will be given to go through per group's work. Plan : Working on Feedback Proceedings: Each group will read their group's feedback form and will try to incorporate the required changes in their work. 150

85 Rubrics of Assessment for Learning Parameter Learner is able to Beginning (1) Approaching (2) Meeting (3) Exceeding (4) Define acids and bases in terms of H+ and OH- List and explain characteristic properties of acids and bases. Define acidity and alkalinity in terms of ph Identify and describe strong and weak acids and bases. Understand the concept of acids and bases in our daily routine 151

86 Parameter Learner is able to Beginning (1) Approaching (2) Meeting (3) Exceeding (4) Describe the role of antacids and understand neutralization using real life problems. Identify acidic, basic and neutral oxides. Explain the preparation of salts and their nature. Identify carbon dioxide, hydrogen gases. 152