11 3,4,5 - Chemistry Mock Exam Revision - Foundation

Transcription

1 3,4,5 - Chemistry Mock Exam Revision - Foundation C2.4 Rates of reaction Revision Foundation Q. Pieces of zinc react with dilute acid to form hydrogen gas. The graph shows how the volume of hydrogen gas produced changes with time. (a) Describe, as fully as you can, how the volume of gas produced changes with time. A student wants to make the reaction take place faster. Some suggestions are given in the table. Put ticks ( ) next to the two suggestions that would make the reaction take place faster. Suggestions ( ) Use bigger pieces of zinc. Use a more concentrated acid. Use zinc powder. Decrease the temperature of the acid. (Total 4 marks)

2 Q2. Hydrogen peroxide (H 2O 2) contains the same elements as water (H 2O). (a) Name the hazard symbol shown by using the correct word from the box. corrosive flammable oxidising toxic () Hydrogen peroxide decomposes in the presence of a catalyst. 2H 2 O 2 (aq) 2H 2 O(l) + O 2 (g) (i) Complete the word equation for this chemical reaction. hydrogen peroxide water +... () What does a catalyst do to a chemical reaction? () (Total 3 marks) Q3. A student investigated the rate of reaction between marble and hydrochloric acid. The student used an excess of marble. The reaction can be represented by this equation: CaCO 3(s) + 2HCl(aq) CaCl 2(aq) + H 2O(l) + CO 2(g) The student used the apparatus shown in the diagram.

3 The student measured the mass of the flask and contents for ten minutes. The results are shown on the graph. Use the graph to answer the questions. (a) (i) Complete the graph by drawing a line of best fit. () Use the graph to find the mass of the flask and contents after.8 minutes.... grams () (iii) The rate of reaction can be measured by the steepness of the graph line. Describe, as fully as you can, how the rate of reaction changes with time in this experiment

4 The mass of the flask and contents decreased during the experiment. Use the equation for this reaction to help you explain why (c) A balance is used to measure the mass of the apparatus. (i) Which balance, A, B, or C, has the highest resolution (most precise)? Balance A Balance B Balance C The balance with the highest resolution is balance () The balance used for this experiment should have a high resolution. Explain why (d) The student repeated the experiment using powdered marble instead of marble chips. The rate of reaction between the marble and hydrochloric acid particles was much faster with the powder. Explain why (Total marks)

5 Q4. A student studied the effect of temperature on the rate of reaction between hydrochloric acid and sodium thiosulphate. The student mixed 50 cm 3 of a sodium thiosulphate solution and 5 cm 3 of hydrochloric acid in a flask. The flask was placed over a cross. The student timed how long after mixing the cross could no longer be seen. (a) (i) Balance the chemical equation for this reaction. Na 2S 2O 3(aq) + HCl(aq) NaCl(aq) + H 2O(l) + SO 2(g) + S(s) () What causes the cross to be seen no longer?... () A graph of the results is shown. (i) What effect does temperature have on the rate of this reaction?... ()

6 Explain why temperature has this effect on the rate of reaction (Total 5 marks) Q5. Sodium thiosulfate solution reacts with hydrochloric acid. As the reaction takes place the solution slowly turns cloudy. The diagram shows a method of measuring the rate of this reaction. A student used this method to investigate how changing the concentration of the sodium thiosulfate solution affects the rate of this reaction. The student used different concentrations of sodium thiosulfate solution. All the other variables were kept the same. The results are shown on the graph below.

7 (a) (i) Draw a line of best fit on the graph. () Suggest two reasons why all of the points do not lie on the line of best fit (i) In a conclusion to the investigation the student stated that: The rate of this reaction is directly proportional to the concentration of the sodium thiosulfate solution. How does the graph support this conclusion? () Explain, in terms of particles, why the rate of reaction increases when the concentration of sodium thiosulfate is increased. (Total 6 marks) Q6. A student investigated the rate of reaction between marble and hydrochloric acid. The student used an excess of marble. The reaction can be represented by this equation. CaCO 3 (s) + 2HC (aq) CaC 2 (aq) + H 2O (l) + CO 2 (g) The student used the apparatus shown in the diagram.

8 The student measured the mass of the flask and contents every half minute for ten minutes. The results are shown on the graph. Use the graph to answer the questions. (a) Complete the graph opposite by drawing a line of best fit. () (c) Why did the mass of the flask and contents decrease with time? After how many minutes had all the acid been used up?... minutes () () (d) The student repeated the experiment at a higher temperature. All other variables were kept the same as in the first experiment. The rate of reaction was much faster. (i) Draw a line on the graph to show what the results for this second experiment might look like. Why does an increase in temperature increase the rate of reaction? (3) (Total 8 marks)

9 Q7. A student does an experiment to examine the rate of reaction between magnesium and dilute hydrochloric acid. She adds 25 cm³ of the acid to a weighed amount of the metal. The reaction produces hydrogen gas. Magnesium + hydrochloric acid magnesium + hydrogen chloride She collects the gas and measures the volume collected at one minute intervals. All the metal reacted but there was some acid left unreacted. Her results are shown on the graph. (a) The diagram shows part of the apparatus she used for the experiment. Complete the diagram to show how the student could collect the hydrogen produced and measure the volume after each minute.

10 (i) When is the rate of reaction at its fastest?... () State one way in which she could increase the rate of reaction.... () (c) (i) What is the total volume of hydrogen collected in the experiment?... cm³ () State one way in which she could increase the final volume of hydrogen collected.... () Q8. Calcium carbonate reacts with dilute hydrochloric acid as shown in the equation below. CaCO 3(s) + 2HCl(aq) CaCl 2(aq) + H 2O(l) + CO 2(g) The rate at which this reaction takes place can be studied by measuring the amount of carbon dioxide gas produced. The graph below shows the results of four experiments, to 4. In each experiment the amount of calcium carbonate, the volume of acid and the concentration of the acid were kept the same but the temperature of the acid was changed each time. The calcium carbonate was in the form of small lumps of marble. (a) Apart from altering the temperature, suggest two ways in which the reaction of calcium carbonate and hydrochloric acid could be speeded up

11 Which graph, to 4, shows the results of the experiment in which the acid had the highest temperature? Experiment... Explain fully how you know. (c) (i) In experiment 2, how does the rate of reaction after one minute compare with the rate of reaction after two minutes? () Explain, as fully as you can, why the reaction rate changes during experiment 2. (Total 7 marks)

12 M. (a) any two from: increases owtte allow goes up until reaches maximum / levels off owtte quickly at first owtte then more slowly / rate decreases allow reaction finished ignore rate increases 2 use a more concentrated acid list principle applies use zinc powder M2. (a) oxidising (i) oxygen ignore any numbers 2 [4] (catalyst) speeds up a (chemical reaction) accept changes the rate (of reaction) [3] M3. (a) (i) curve missing anomalous point answer in the range of to 00.5 (iii) reaction goes quickly at first accept reaction slows down reaction stops because carbon dioxide is produced accept gas is produced carbon dioxide / gas escapes, therefore the mass of the flask and contents decreases

13 (c) (i) balance B because during the experiment a gas / carbon dioxide escapes from the flask therefore the balance needs a high resolution to measure the small changes in the mass (d) the (marble) powder has a larger surface area than the (marble) chips therefore there would be more collisions with the acid particles (within the same amount of time) [] M4. (a) (i) Na 2S 2O 3(aq) + 2 HCl(aq) 2NaCl(aq) + H 2O(l) + S(s) + SO 2(g) (formation of) sulphur accept precipitate or solid produced do not accept goes cloudy or milky (i) heat temperature increased temperature increases (the rate of reaction) or decreased temperature decreases rate of reaction may be gained in part if stated and not implied (these ideas may be given in (i)) particles have more kinetic energy accept particles move faster more collisions (so more reactions) more energetic collisions two marks [5]

14 M5. (a) (i) a continuous straight line missing anomalous point allow a line which does not start at zero / origin any two sensible errors eg timing errors and / or example(*) measurement errors and / or example(*) apparatus errors and / or example(*) human / experimental / random error and / or example or did not do it right (*) (*)could be two from same category eg two timing errors watch not started at the same time plus difficulty in deciding when the cross has disappeared. temperature fluctuation anomalous point accept outlier / wrong result results not recorded correctly plotting error rate calculated incorrectly ignore not repeated ignore systematic / zero error / weighing error or error unqualified 2 (i) straight line or as concentration increases the rate goes up or converse accept numerical example accept positive correlation accept same gradient ignore most points near / on line of best fit more collisions accept greater chance of collisions accept collide more successfully accept alternative versions of collide eg bump / hit ignore references to energy / speed of particles / surface area

15 more particles (in each volume of solution)(i.e. an attempt at defining concentration) accept particles are closer together allow ions / atoms / molecules for particles ignore reactants accept greater frequency of collisions or greater number of collisions per second for 2 marks M6. (a) sensible line of best fit which goes through or close to all the points except the anomalous point [6] loss of gas / loss of CO 2 idea of gas produced / formed (c) 7 (d) (i) steeper line from around the same starting point and left of the points allow crosses if they are fully correct for mark levelling off at 99 accept short level line at 99 ± ½ square any three from: particles / molecules / atoms/ ions have more energy allow given / gain / get energy move faster ignore move about more ignore vibrate more / faster collide more often or more chance of collisions or bump into each other more ignore collide quicker / faster collide with more force / energy or more particles have the activation energy or more collisions result in reaction or more collisions are successful 3 [8]

16 M7. (a) (must be possible for the gas to enter and displace the water) or other suitable apparatus apparatus to collect the gas correctly assembled for mark calibrated collection vessel (award even if diagram is wrong) for mark (i) at the start / in the first /2 minutes (or any time within this range) for mark increase the temperature / use smaller pieces of metal / use more metal / increase the surface area of the metal / add a catalyst / shake the flask / increase the concentration / strength of the acid for mark 2 (c) (i) 48 for mark increase the amount of magnesium used for mark (do not allow increase the amount of acid used) [6] M8. (a) increase concentration of acid; increase surface area of solid or grind up the solid; add a catalyst any two for mark each ; it is the one that makes the gas fastest (steeper curve etc) (second part is dependant on first) for mark each (c) (i) faster after one minute, slower after 2 minutes for mark 2 2 the reactants get used up; so concentration decreases/less chance of collision for mark each 2 [7]

17 C2.5 Exothermic and endothermic reactions Revision Foundation Q. Distress flares are used to attract attention in an emergency. Flares often contain magnesium. Magnesium burns to form magnesium oxide. (a) The distress flare burns with a bright flame because the reaction is very exothermic. Complete the following sentence using the correct words from the box. gives out heat stores heat takes in heat An exothermic reaction is one which... () Indigestion tablets can be made from magnesium oxide. The magnesium oxide neutralises some of the hydrochloric acid in the stomach. Draw a ring around the name of the salt formed when magnesium oxide reacts with hydrochloric acid. magnesium chloride magnesium hydroxide magnesium sulfate () Q2. An indigestion tablet contains sodium hydrogencarbonate and citric acid. When the tablet is added to cold water a chemical reaction takes place and there is a lot of fizzing. (a) The formula of the gas that causes the fizzing is CO 2 Name this gas.... ()

18 This chemical reaction is endothermic. (i) Tick ( ) the statement which describes what happens to the temperature of the solution. Statement Tick ( ) The temperature of the solution will increase. The temperature of the solution will decrease. The temperature of the solution will stay the same. () Tick ( ) the statement which describes what happens to the energy during the reaction. Statement Tick ( ) Energy is given out to the surroundings. Energy is taken in from the surroundings. No energy is given out to or taken from the surroundings. () Q3. Instant cold packs are used to treat sports injuries. One type of cold pack has a plastic bag containing water. Inside this bag is a smaller bag containing ammonium nitrate. The outer bag is squeezed so that the inner bag bursts. The pack is shaken and quickly gets very cold as the ammonium nitrate dissolves in the water. (a) One of the statements in the table is correct. Put a tick ( ) next to the correct statement. Statement ( ) The bag gets cold because heat energy is given out to the surroundings. The bag gets cold because heat energy is taken in from the surroundings. The bag gets cold because plastic is a good insulator. ()

19 Draw a ring around the word that best describes the change when ammonium nitrate dissolves in water. electrolysis endothermic exothermic () (c) Suggest and explain why the pack is shaken after the inner bag has burst. (Total 4 marks) Q4. The diagram shows some magnesium ribbon burning. (a) Choose words from the list to complete the sentences below. electrical heat light kinetic an endothermic an exothermic a neutralisation a reduction When magnesium burns, it transfers... and... energy to the surroundings. We say that it is... reaction. (3) Complete the word equation for the reaction. magnesium + magnesium oxide () (Total 4 marks)

20 Q5. The diagram shows the apparatus for an experiment. Hydrated copper sulphate crystals were heated. They became anhydrous copper sulphate. (a) Name a suitable piece of equipment to heat tube A. () Use words from the box to complete the two spaces in the table. You may use each word once or not at all. black blue orange red purple white Name Colour Hydrated copper sulphate crystals... Anhydrous copper sulphate... (c) What is the purpose of the ice and water in the beaker? ()

21 (d) Drops of a clear, colourless liquid formed on the inside of tube B. (i) Name the liquid. () Explain how the liquid came to be inside tube B. (e) Anhydrous copper sulphate can be turned into hydrated copper sulphate. What would you need to add? Apart from the change in colour, what could you observe? (f) Copper sulphate can be made from black copper oxide by reacting it with an acid. Name the acid. () (Total 0 marks) Q6. A student did two experiments using ammonium chloride. (a) In the first experiment the student heated a small amount of ammonium chloride in a test tube.

22 Two reactions take place in the test tube. Reaction Reaction 2 ammonium chloride ammonia + hydrogen chloride (colourless gases) ammonia + hydrogen chloride ammonium chloride (i) Complete the sentences by crossing out the incorrect word in each box. Reaction takes place at a high low temperature. Reaction 2 takes place at a high low temperature. () Draw a ring around the word which best describes reactions and 2. combustion displacement oxidation reduction reversible () (iii) Suggest a reason for the mineral wool at the top of the test tube. () In the second experiment the student mixed a small amount of ammonium chloride with some water in a beaker. The temperature of the water was measured before and after adding the ammonium chloride. Temperature before adding the ammonium chloride Temperature after adding the ammonium chloride 20 C 6 C Draw a ring around the word which best describes the process which takes place. combustion displacement endothermic exothermic freezing () (Total 4 marks)

23 M. (a) gives out (heat) magnesium chloride [2] M2. (a) carbon dioxide must be name do not accept carbon oxide (i) the temperature of the solution will decrease (list principle) energy is taken in from the surroundings (list principle) [3] M3. (a) the bag gets cold because heat energy is taken in from the surroundings endothermic (c) any two from: mix / spread (the ammonium nitrate and water) dissolve faster(*) get cold faster or so the whole bag gets cold(*) (*)allow increase rate or quicker reaction particles collide more or more collisions M4. (a) heat light an exothermic in any order for mark each 2 3 [4] oxygen / O 2 for mark [4]

24 M5. (a) Bunsen (burner) accept spirit burner do not credit candle blue white credit () if both colours correct but answers are reversed to cool the tube (B) accept answers which anticipate part (d) e.g. to condense the water vapour or gases or vapours (d) (i) water do not credit condensation (Water) vapour from the crystals (from tube A) accept steam or steam from tube A condenses or cools accept turns to (liquid) water (e) add water gets hot or hotter or warm or warmer turns into solution dissolves or the temperature rises or there is an exothermic reaction accept steams or hisses ignore any reference to colour(s) 2 (f) sulphuric acid accept H 2S0 4 only if correct in every detail [0] M6. (a) (i) high and low both needed for mark (iii) reversible to prevent ammonium chloride / solid / particles escaping idea of a filter do not accept to prevent gases escaping endothermic [4]

25 C2.6 Acids, bases and salts Revision Foundation Q. (a) The diagram shows one way of making crystals of copper sulphate. (i) Why was the solution filtered?... () How could you make the crystals form faster from the copper sulphate solution?... () (iii) The chemical equation is shown for this reaction. CuO(s) + H 2SO 4(aq) CuSO 4(aq) + H 2O(l) In the chemical equation what does (aq) mean?... () Blue copper sulphate crystals go white when warmed. How could you use the white copper sulphate as a test for water? (Total 5 marks)

26 Q2. A solution of Y was slowly added to a solution of X. The graph shows how the ph of the resulting solution changed. (a) (i) What was the ph of solution X before any of solution Y was added? () State whether solution Y was acidic, alkaline or neutral. () (iii) What volume of solution Y was needed to react with all of the substance in solution X?... cm 3 () The chemical equation shows the reaction between an acid and an alkali to form a salt and water. (i) Draw a circle round the formula of the alkali. H 2SO 4 + 2KOH K 2SO 4 + 2H 2O () What is the formula of the salt? () (Total 5 marks)

27 Q3. Salts can be prepared by the reaction of acids with alkalis. (a) (i) The reactions of acids with alkalis can be represented by the equation below. Choose a substance from the box to complete the equation. carbon dioxide hydrogen oxygen water acid + alkali salt +... () Draw a ring around the word which best describes the reaction. displacement neutralisation oxidation reduction () Sodium sulphate is an important salt. The table gives a list of some substances. Put a tick ( sulphate. ) next to the names of the acid and the alkali that would react to make sodium Substances ( ) Hydrochloric acid Nitric acid Potassium sulphate Sodium hydroxide Sodium nitrate Sulphuric acid Q4. (a) Citric acid produces hydrogen ions in aqueous solution. These ions can be represented as H + (aq). Complete this sentence. The (aq) means that the acid has been dissolved in.... () (c) Citric acid is a weak acid. Draw a ring around the correct answer to complete the sentence. has a low boiling point. The word weak means that the acid is dilute. is partially ionised in water. ()

28 (d) A student measured the ph of four acids, A, B, C and D. The acids were the same concentration. The same quantity of magnesium ribbon was added to each of the acids. The volume of gas produced after 5 minutes was recorded. The results are shown in the table. Acid ph Volume of gas in cm 3 A 2 8 B 5 6 C 24 D 4 2 (i) State one way in which the student made sure that the experiment was fair. () Use the results to arrange the acids, A, B, C and D in order of decreasing acid strength. Most acidic... Least acidic. () (e) When acids react with alkalis, the hydrogen ions from the acid react with the hydroxide ions from the alkali. (i) Which one of the following represents the formula of a hydroxide ion? Draw a ring around your answer. H O OH () Draw a ring around the correct answer to complete the sentence. acidic. A solution with more hydrogen ions than hydroxide ions is alkaline. neutral. () (Total 7 marks)

29 Q5. Nitric acid can be neutralised by alkalis to make salts. (i) The salt called potassium nitrate can be made from nitric acid. Complete the word equation for this neutralisation reaction. Choose the correct substances from the box. hydrogen oxygen potassium chloride potassium hydroxide water nitric acid +... potassium nitrate +... Ammonium nitrate is another salt made from nitric acid. Which one of the following is the main use of ammonium nitrate? Draw a ring around your answer. dye fertiliser plastic fuel () (iii) Complete this sentence by choosing the correct ion from the box. H + NH 4 + NO3 O 2 OH The ion that makes solutions acidic is.... () (Total 4 marks) Q6. A student tried to make some magnesium sulphate. Excess magnesium was added to dilute sulphuric acid. During this reaction fizzing was observed due to the production of a gas. (i) Complete and balance the chemical equation for this reaction H 2SO (3)

30 At the end of the reaction the solution remaining was filtered. Why was the solution filtered? () (iii) The filtered solution was left in a warm place. Explain why the filtered solution was left in a warm place. (Total 6 marks) Q7. Ammonium nitrate and ammonium sulphate are used as fertilisers. (i) Which acid reacts with ammonia to form ammonium nitrate?... () Which acid reacts with ammonia to form ammonium sulphate?... () (iii) The reactions in (i) and are both exothermic. How can you tell that a reaction is exothermic?... () (iv) The reactions in (i) and are both examples of acid + base reactions. What is the name of the chemical change which takes place in every acid + base reaction?... () (Total 4 marks)

31 Q8. The following passage is about the preparation of lead iodide, an insoluble salt. An excess of potassium iodide in solution was shaken with some lead nitrate solution in a test tube. The lead iodide precipitate was separated from the mixture and then washed several times with water. The lead iodide was dried and then placed in a bottle. (a) Suggest a reason why excess potassium iodide was used. () What word used in the passage shows that lead iodide is insoluble?... () (c) Suggest how lead iodide can be separated from the mixture () (d) Why was the lead iodide washed with water? () (e) Suggest a method which could be used to dry this lead iodide () (f) Lead compounds are toxic. Suggest a suitable safety precaution that should be taken when using toxic substances in laboratories.... () (Total 6 marks)

32 Q9. The diagrams show what happens when an acid is added to an alkali. (a) What is present in the flask at stage 2, besides universal indicator and water? () Write an ionic equation to show how water is formed in this reaction and state the sources of the ions. (3) (Total 4 marks)

33 M. (a) (i) to remove or separate copper oxide accept to remove or separate unreacted or excess base accept to remove or separate insoluble solids heat (the solution) accept heat the water accept evaporate the water rapid cooling/cool to lower temperature accept boil the water or solution not increase surface area, put in draught not increase the temperature (iii) aqueous accept in water accept solution not soluble in water add water/liquid/solution colour changes to blue [5] M2. (a) (i) allow a number between 2.5 and 3 (inclusive) accept just under 3 or about 3 alkaline or alkali (iii) 25 ignore any reference to units (i) a circle round KOH or 2 KOH K 2SO 4 do not credit potassium sulphate [5]

34 M3. (a) (i) water accept H 2O accept correct ringed answer in box neutralisation accept underlining or any indication, eg tick sodium hydroxide sulphuric acid apply list principletotal M4. (a) water / H 2O / hydrogen oxide [4] is partially ionised in water (d) (i) eg same concentration / quantity of Mg accept: volume of acid / ribbon for both / same time accept: volume of gas measured under the same conditions C A D B (e) (i) OH acidic [7] M5. (i) potassium hydroxide accept correct formulae water fertiliser (iii) H + accept hydrogen but not H [4]

35 M6. (i) Mg + (H 2SO 4) MgSO4 + H 2 deduct mark if not balanced only if all three correct accept alternative metal of similar reactivity for example Zn or Fe candidate would not then be awarded first mark for Mg then error carried forward deduct mark if not balanced only if all three correct to remove the (excess) magnesium accept separate accept insoluble substances or solids or residue do not accept unreactive substances or impurities or remove magnesium from sulphuric acid (iii) to evaporate (some of the water or solution) to form crystals or crystallise accept to form a saturated solution or concentrated solution do not accept to leave MgSO 4 [6] M7. NOTE In this question and throughout the Paper, if the name of a chemical is asked for, then the formula is acceptable only if it is correct in every detail. If the name is correct and the candidate has tried to be helpful by giving, in addition, an incorrect version of the formula, then this is acceptable provided it does not lead to ambiguity. (i) nitric (acid) accept HN0 3 sulphuric (acid) accept H 2SO 4

36 (iii) heat given out or temperature rise or energy given out or steam do not credit just use a thermometer do not credit just 'change in temperature' (iv) neutralisation accept neutralise accept neutral accept formation of salt or water do not credit exothermic [4] M8. (a) all lead nitrate reacted or no lead nitrate left or enough KI to react with lead nitrate or to remove all the lead ions or to get maximum amount of I 2 ignore comments about speed do not accept to remove all the lead precipitate allow phonetic spelling do not accept ppt (c) (d) filter / filtration / centrifuge / decant do not accept sieve any one from: removes (soluble) impurities

37 removes (unreacted) KI removes KNO 3 removes (excess) solution removes nitrates purifying is insufficient do not accept removes potassium do not accept removes iodide (e) answer based on filter paper, desiccator, suitable solvent (gentle) heat, drying cabinet, oven etc. Accept any method of heating i.e. bunsen / hairdryer etc. Accept leave to evaporate / stand or leave in a warm room e.g. place between dry filter paper, allow to dry e.g. use propanone, allow to dry e.g. leave on sunny window sill e.g. leave in a draught the answer leave / evaporate / draught alone is insufficient [6] (f) wear gloves / mask or fume-cupboard or wash hands afterwards ignore goggles / labcoat or extractor fan / do not touch etc. M9. (a) sodium ions and chloride ions (not chlorine) allow sodium chloride/salt/common salt for mark H + + OH H 2O H + from (hydrochloric) acid OH - from alkali/sodium hydroxide lose mark if no charge shown disregard other ions each for mark 3 [4]

38 C2.7 Electrolysis Revision Foundation Q. The electrolysis of sodium chloride solution produces useful substances. (a) (i) Choose a word from the box to complete the sentence. covalent ionic non-metallic Electrolysis takes place when electricity passes through... compounds when they are molten or in solution. () Choose a word from the box to complete the sentence. alkenes elements salts During electrolysis the compound is broken down to form... () The diagram shows an apparatus used for the electrolysis of sodium chloride solution. Identify the products A, B and C on the diagram using substances from the box. chlorine gas hydrogen gas oxygen gas sodium hydroxide solution sodium metal (i) A is... B is... (iii) C is... () () () (Total 5 marks)

39 Q2. A student investigated the electrolysis of lead bromide. Lead bromide was placed in the tube and the circuit was switched on. The light bulb did not light up. The tube was heated and soon the bulb lit up. The observations are shown in the table. Positive electrode red-brown gas Negative electrode silver liquid (a) What is meant by electrolysis?... Why did the lead bromide conduct electricity when the tube was heated?... () (c) Name the substances formed at the: positive electrode;... negative electrode.... (d) Suggest one safety precaution that should be taken during this investigation.... () (Total 6 marks)

40 Q3. Electrolysis can be used to remove unwanted hair from the skin. The positive electrode is connected by a patch to the skin. The negative electrode is connected to the hair. The body fluid is a solution that contains sodium chloride. The electricity causes the electrolysis of a small amount of this solution. (a) In this solution hydrogen ions move to the negative electrode. Complete the sentence using one word from the box. negative neutral positive Hydrogen ions move to the negative electrode because they have a... charge. () Draw a ring around the name of the gas produced at the positive electrode during the electrolysis of sodium chloride solution. chlorine hydrogen nitrogen () (c) The electrolysis of the sodium chloride solution forms a strong alkali around the hair follicle. (i) Complete the name of this strong alkali using one of the words from the box. chlorine hydrogen nitrogen The name of this strong alkali is sodium.... () Suggest how this strong alkali helps to remove the hair. () (Total 4 marks)

41 Q4. The electrolysis of sodium chloride solution is an important industrial process. The apparatus shown below can be used to show this electrolysis in the laboratory. (a) Name gas A.... () Chlorine is produced at the positive electrode. Describe and give the result of a chemical test to prove that the gas is chlorine. (c) Chloride ions move to the positive electrode. Explain why. () (d) A small quantity of chlorine is added to drinking water. Explain why. () (e) The solution around the negative electrode becomes alkaline. Name the ion which makes the solution alkaline. () (Total 6 marks)

42 Q5. Read the information in the box and then answer the question. Aluminium is made by the electrolysis of aluminium oxide. Aluminium oxide is an ionic compound containing aluminium ions (Al 3+ ) and oxide ions (O 2 ). The diagram below shows the apparatus used to electrolyse aluminium oxide. (a) In this question you will get marks on using good English, organising information clearly and using specialist terms correctly. Use information in the box and your knowledge and understanding of this process to answer this question. Explain, as fully as you can, how aluminium and carbon dioxide are formed in this process (6) Explain why cryolite is added

43 M. (a) (i) ionic elements (i) chlorine (gas) allow Cl 2 / Cl / Cl 2 allow chloride hydrogen (gas) allow H / H 2 / H 2 (iii) sodium hydroxide (solution) allow NaOH allow sodium solution [5] M2. (a) breakdown / decomposition / splits into elements / not ions separates into elements / produce a chemical reaction using electricity lead bromide melted / free ions not electrolyte (c) (+) bromine element must be appropriate to electrode ( ) lead element must be appropriate to electrode (d) fume cupboard / protective clothing allow safety glasses not safety mat

44 [6] M3. (a) positive accept + or +ve or plus chlorine (c) (i) hydroxide Any indication of hydro destroys / damages / dissolves (owtte) the hair / follicle / root allow burns / reacts with the hair ignore incorrect name of compound [4] M4. (a) hydrogen accept H 2 do not accept H litmus paper / Universal Indicator paper / ph paper allow any suitable named indicator bleached / turns white or loses its colour do not accept bleached cloth / leaves etc. allow second mark unless incorrect indicator given allow starch iodide paper () goes black / blue black () allow potassium iodide solution () goes brown / orange / black precipitate () (c) because they have a negative charge or opposite charges attract accept (because) it is Cl accept chlorine, Cl or chlorine ions has a negative charge do not accept Cl on its own do not accept Cl 2 o.e. has negative charge (d) kill bacteria / germs, etc. or sterilise / disinfect accept destroys bacteria etc. ignore clean / purify water (owtte) do not accept just gets rid of bacteria (e) hydroxide (ion) accept OH [6]

45 M5. (a) Marks awarded for this answer will be determined by the Quality of Written Communication (QWC) as well as the standard of the scientific response. No relevant content. There is a brief description of the electrolysis of aluminium oxide. There is some description of the electrolysis of aluminium oxide. There is a clear, balanced and detailed description of the electrolysis of aluminium oxide. 0 marks Level ( 2 marks) Level 2 (3 4 marks) Level 3 (5 6 marks) examples of the chemistry points made in the response aluminium oxide is melted / made liquid aluminium ions are attracted to the negative electrode at the negative electrode aluminium is formed or aluminium ions gain electrons oxide ions are attracted to the positive electrode oxygen is formed at the positive electrode or oxide ions lose electrons the oxygen reacts with carbon to make carbon dioxide or carbon dioxide formed at positive electrode. Lowers melting point. Less energy/electricity needed Saves money