Chemistry 12 Holiday Homework. Part 1: A Focus on the Amphoteric Nature of Acids and Bases

Transcription

1 Chemistry 12 Holiday Homework Part 1: A Focus on the Amphoteric Nature of Acids and Bases Total Marks /37 Student: 1. a) Describe the difference between polyprotic and amphiprotic in relation to acids. [2] _ b) Name the one polyprotic acid that is not amphiprotic and explain why it is not amphiprotic. Show the reactions that prove it is not amphiprotic. [3] _ 2. Now you will apply your knowledge of equilibrium and equilibrium constants to weak acids. If we are given the general equation for a weak acid then: a) What will the general equation be for the Keq of this equilibrium? [1] Keq = b) Given the following weak acid equilibrium write the Keq equation. [1] Keq = 3. Most weak acids strongly favour the reactants. Do you think the Keq value will be: [1] a. Keq > 1 b. Keq = 1 c. 1 < Keq < 10-3 d. Keq < 10-4

2 4. a) What is the definition of a Lewis acid? [2] _ b) Why is BF 3 considered a Lewis acid. Use the reaction between BF 3 and NH 3 to help with your explanation. [2] c) Draw the electron dot diagram for both BF 3 and NH 3. [4] d) Use Google search as a resource to determine what happens to the lone pair electrons on ammonia during the reaction with BF 3. Show what is happening at an electron level during this reaction in the space below. One of the two reactants is already shown below. [3] e) You are given the following equation below for the equilibrium involving the weak acid vinegar. a) What is the correct equation for vinegars equilibrium in water? What should you write instead of the equation written above? [1]

3 b) If you are told the Keq for this equilibrium is 1.8 x 10-5 at 25 o C and that the equilibrium concentration of vinegar is 3.12 M, how many moles of H + ion will there be at equilibrium? [3] c) If the equation for ph is: ph = - log [H + ] what is the ph of the above equilibrium in part b) that is at 25 o C? Show your work. [2] d) What is the percentage of H + ions to HC 2 H 3 O 2 at equilibrium at 25 o C? [2] 5. Bases are also amphoteric. Use the following chemguide links to help you answer the questions below a) Explain why Aluminium oxide is an amphoteric substance. Write two reactions that prove it is amphoteric. [3] Reaction 1: Reaction 2:

4 b) Write two reactions that prove that Al(OH) 3 is also amphoteric. [2] Reaction 1: Reaction 2: c) Even Aluminium metal is considered amphoteric. Write two reactions that prove this. [2] Reaction 1: Reaction 2: Part 2 : Research Component Total Marks /55 The acidification of the world s oceans is becoming a focus. This section is to help you understand the chemistry involved in this process and the impact of this chemistry. 1. State five possible reasons for global CO 2 levels in our atmosphere rising. [5]

5 2. Explain how CO 2 is able to dissolve into water and state three factors that affect the amount of CO 2 that is able to dissolve in water. [4] 3. Where in the world might you expect to find the highest levels of CO 2 dissolving into water? Explain your answer. [2] 4. Once the CO 2 dissolves into water it is able to react with water. Write this equilibrium equation. [1] 5. The acid that is formed by the reaction you wrote in question 4 is able to ionise to produce H+ ions and then ionise again. Show the equilibrium equation for both these steps. [3]

6 6. Use all of the above reactions on the previous page to help explain how raising CO 2 levels in the atmosphere can acidify the world s oceans. Make sure to apply Le Chatelier s Principle. [3] 7. The carbonate produced from the reaction equilibrium written in question 5 is able to react with calcium in the ocean. Explain why this is such a large problem for all wildlife in our oceans and state which species will be most affected? [5]

7 8. What is a volcanic CO 2 seep and what impact does it have on the local environment in an ocean. [4] 9. State five other factors that are killing off wildlife in our oceans and how they are killing off our wildlife. [5]

8 10. Explain what causes acid rain and why the acid rain became more acidic during the industrial revolution and in the regions where large scale industry exists. [5] 11. Write three different reactions between gases and water that can result in acid rain. [3]

9 12. Explain the impact on acid rain on soil ph as well as minerals found in the soil. Make sure to discuss the chemistry involved. [6] 13. Explain how acid rain is impacting vegetation and why it has this impact. [4]

10 14. Bibliography. State the sources of your information and make sure to number then and reference these numbers in your written answers. [5] Note: You should only use edu education sites not wiki websites. The websites used must be of high quality not the first ones you get in a Google search. Volumetric analysis- Acid base titration questions from the Essential chemistry book, Set 7: Q1-10. Submit the answers.

11 YEAR 12 CHEMISTRY UNIT-3 PRACTICE questions On STOICHIOMETRY Submit the answers in week 1 term 1, NO VALIDATION TEST. 1 Silicon carbide which is also known Carborundum is the very hard, black substance used on many abrasive papers (sand paper). It is made by heating a mixture of 1.0 kg quartz (SiO 2 ) and 1.0 kg of carbon (C) to a very high temperature to produce silicon carbide (SiC) and carbon dioxide. (a) Write a balanced equation for this reaction. (b) What is the maximum amount of carborundum that can be produced in this reaction? (c) What mass of excess reagent is left over. (d) Calculate the mass of the limiting reagent needed to completely react with the excess reagent. 2 The following equation describes the reaction between sulfur tetrafluoride and diiodine pentaoxide. 5 SF 4 (g) + 2 I 2 O 5 (s) 4 IF 5 (l) + 5 SO 2 (g) g of I 2 O 5 is shaken with 6.02 L of SF 4 at 76 0 C and 120 kpa for completion of reaction. (i) (ii) What volume of SO 2 is produced at 76 0 C and 120 kpa? What mass of each of the substances (reactants and products) is present at the completion of the reaction? 3 When potassium carbonate solution is added to a solution of calcium nitrate, a precipitate of calcium carbonate is formed. 25 ml of mol L -1 potassium carbonate is added to 15 ml of 1.05 moll -1 calcium nitrate solution. Calculate (i) (ii) the mass of calcium carbonate precipitated the concentration of calcium ions in the final solution. 4 A 5.39 g sample of impure calcium carbonate is dissolved in excess HCl. The resulting 593 ml of carbon dioxide is collected over water at 24 0 C and 102 kpa. At this temperature water has a vapour pressure of 2.98 kpa. Determine the percentage purity of calcium carbonate.

12 5 The predominant anions in seawater are Cl - (aq) and SO 4 2- (aq). Two chemistry students had designed an experiment to determine the concentration of these ions in seawater. They first added excess Ba(NO 3 ) 2 (aq) to 325 ml of seawater causing the precipitation of BaSO 4 (s). The precipitate was filtered, washed and dried and found it had a mass of 2.65 g. To the filtrate the students added excess AgNO 3 (aq) precipitating the chloride ion the sea water as AgCl(s) and 23.3 g of AgCl (s) was obtained. Using their data, find the concentration of Cl - (aq) and SO 4 2- (aq) in the seawater sample. Express your answer in g L Gemma and her partners conducted an investigation into the reaction between magnesium and hydrochloric acid. To this they added a weighed piece of magnesium and allowed the hydrogen that formed to escape. The flask with its contents was reweighed after the reaction was complete. The following data was recorded: mass of conical flask + HCL solution g mass of Mg added g mass of conical flask + HCL solution + Mg after reaction g a. Write a balanced chemical equation for the reaction between hydrochloric acid and magnesium. b. Why is the mass of the conical flask + HCL solution + Mg after reaction less than the mass of the conical flask +HCL solution +Mg before the reaction? c. What mass of hydrogen was formed in the reaction? d. By a suitable calculation, show that magnesium was an excess reagent. 7 Magnesium metal reacts with dilute HCl to form hydrogen gas. Mg (s) + 2 HCl (aq) MgCl 2 (aq) + H 2 (g) (i) (ii) (iii) (iv) g of magnesium is added to 50.0 ml of mol/l HCl. Which reactant is the limiting reagent? [5 marks] Calculate the mass of Mg remaining. Calculate the number of moles of Hydorgen ion remaining Calculate the volume of hydrogen gas produced at 25 0 C and kpa [3 marks]. (v) Calculate the concentration of Mg ion in the 50.0 ml solution.

13 8 Sodium pyrosulfate, Na 2 S 2 O 7, is produced by the following series of reactions: S + O 2 SO 2 2SO 2 + O 2 2SO 3 SO 3 + H 2 O H 2 SO 4 2H 2 SO 4 + Na 2 CO 3 2NaHSO 4 + H 2 O + CO 2 2NaHSO 4 Na 2 S 2 O 7 + H 2 O In the commercial production of Na 2 S 2 O 7, 17.5 kg of sulfur is consumed in the production of 50.0 kg of Na 2 S 2 O 7. Calculate the percentage efficiency of the process. 9 Inside a blast furnace for the extraction of iron from iron ore many different reactions task place. One important series of reactions for the extraction of iron is shown here: C(s) + O 2 (g) CO 2 (g) C(s) + CO 2 (g) 2CO(g) Fe 2 O 2 (s) + 3CO(g) 2Fe(l) + 3CO 2 (g) (a) Write an overall equation showing the formation of Fe from fe 2 O 3. (b) Assuming no other reactions are involved, determine the minimum amount of carbon needed for every tonne of iron ore if the ore contains 97% Fe 2 O 3 by mass. 10 A technician is to determine the level of calcium in the bloodstream of an elderly hospital patient who is suffering from osteoporosis (a disease where insufficient calcium causes weakened bones). She adopts the following procedure. She takes a ml sample of blood from the patient, and dilutes it to ml. She then takes a ml sample of the diluted solution, and the calcium is precipitated as calcium oxalate, CaC 2 O 4. The precipitate is washed and dissolved in excess dilute sulfuric acid, and then titrated at 60 0 C with moll -1 potassium permanganate. After several repetitions of the experiment, the average volume of potassium permanganate solution required to complete the reaction is 9.88 ml. (a) (b) Write redox equation for the titration reaction. Calculate the mass of calcium present in the original 15.0 ml sample of the patient s blood.

14 11 A piece of bronze (consisting of tin and copper) weighing 25.6 g was cut into small pieces and placed into a dilute sulfuric acid solution so that all of the tin was converted to Sn 2+ ions. The solution was filtered to remove the solid copper. This solution was then mixed with enough distilled water to correctly fill a ml volumetric flask ml samples of the solution were titrated with a mol L -1 potassium permanganate solution. The average volume of potassium permanganate used was 31.7 ml. (a) Write the balanced equation for the oxidation of the Sn 2+ ions by KMnO 4. (b) Calculate the average number of moles of KMnO 4 used. (c) Calculate the number of moles of Sn 2+ in 20.0 ml of solution. (d) Calculate the number of moles of Sn 2+ in ml of solution. (e) Calculate the percentage by mass of tin and copper in bronze. 12 The analysis of some household cloudy ammonia cleaner involved diluting a 50.0 ml sample of a cleaner to a volume of ml then titrating this diluted solution. The diluted sample was found to have an NH 3 (aq) concentration of mol/l. What is the percentage by mass of ammonia in the original cloudy ammonia if it has a density of g/ml? 13 A sample of g of a chlorofluorocarbon ( a compound containing carbon, fluorine and chlorine only) was analysed as follows: All the carbon in the sample was converted into carbon dioxide gas, and all its chlorine was converted into hydrochloric acid. The carbon dioxide weighed g, and the hydrochloric acid formed required 41.0 ml of mol L -1 sodium hydroxide solution for complete neutralisation. Another sample of the same gaseous compound of mass g occupied ml at S.T.P. a) Determine the empirical formula of the compound. b) Determine the molecular formula of the compound. c) Name and draw a possible structure of the compound.

15 14 The percentage purity of a sample of manganese (IV) oxide, MnO 2, can be found by treatment with an excess of a standard sodium oxalate solution in the presence of dilute sulfuric acid. The Mn 4+ ions are reduced to Mn 2+ and the oxalate ions [C 2 O 2-4 ] are oxidized to carbon dioxide gas in this reaction. After the reaction is complete, the excess sodium oxalate is titrated with a standardized potassium permanganate solution. One such impure sample of manganese(iv) oxide of mass g was reacted with ml of acidified mol L -1 sodium oxalate. The mixture was boiled gently to dissolve the solid. After cooling, the solution was titrated with mol L -1 potassium permanganate solution. The volume of the potassium permanganate solution required was ml. Calculate the percentage purity of the manganese (IV) oxide sample. 15 α-amino acids are the building blocks from which all proteins are made. One such amino acids is alanine. It contains the elements C, H, O and N. To determine its empirical formula a g sample was completely burnt in oxygen. The resulting carbon dioxide and water collected and found to weigh and g respectively. The nitrogen contained in the sample was released during combustion and collected as nitrogen gas. When isolated, the nitrogen gas had a volume of ml at kpa and K. (i) Determine the empirical formula for alanine. Further analysis showed alanine has a molar mass of 88.7 moll -1. Determine its molecular formula.