2 Set up an apparatus for simple distillation using this flask.

Transcription

1 The following instructions are from an experimental procedure for the preparation of cyclohexene from cyclohexanol and concentrated phosphoric acid. Read these instructions and answer the questions that follow. Place 25 cm 3 of cyclohexanol into a round-bottomed flask with some porous pot to act as anti-bumping granules. Add 0 cm 3 of concentrated phosphoric acid carefully while shaking the flask. Cool the flask under the tap if it gets too hot. Make sure the reagents are thoroughly mixed. 2 Set up an apparatus for simple distillation using this flask. 3 Warm the flask, gently at first, for about 5 minutes. Then increase the heating so that cyclohexene begins to distil over. Collect the fraction that distils below 95 C. State the purpose of the anti-bumping granules. () (b) Name the part of the distillation apparatus where cyclohexene vapour is changed back into a liquid. Draw a simple diagram of this part of the apparatus. Name... Diagram (2) (Total 3 marks) Page of 80

2 2 Some alcohols can be oxidised by an acidified solution of potassium dichromate(vl). Aldehydes can be oxidised by Tollens reagent or by Fehling s solution. An unknown pure liquid A contains only a single alcohol. Outline a simple procedure to allow you to determine whether A is a primary, a secondary or a tertiary alcohol (Total 3 marks) 3 This question is about cobalt chemistry. Consider the following reaction scheme that starts from [Co(H 2 O) 6 ] 2+ ions. W, X and Y are ions and Z is a compound. For each of the reactions to 4, identify a suitable reagent. Page 2 of 80

3 Identify W, X, Y and Z and write an equation for each of reactions to 4. (Extra space)... (2) (b) A flue-gas desulfurisation process involves the oxidation, by oxygen, of aqueous sulfate(iv) ions (SO 3 2 ) into aqueous sulfate(vi) ions (SO 4 2 ). This reaction is catalysed by Co 2+ ions in an acidic aqueous solution. Write an equation for the overall reaction of sulfate(iv) ions with oxygen to form sulfate(vi) ions. Suggest why this overall reaction is faster in the presence of Co 2+ ions. Page 3 of 80

4 Suggest a mechanism for the catalysed reaction by writing two equations involving Co 2+ and Co 3+ ions. You will need to use H + ions and H 2 O to balance these two equations. (4) (Total 6 marks) Page 4 of 80

5 4 Salicylic acid can be used to make aspirin. Before using a sample of salicylic acid to make aspirin, a student purified the acid by recrystallisation. The method for recrystallisation is outlined below. Step : The sample is dissolved in a minimum volume of hot water. Step 2: The solution is filtered hot. Step 3: The filtrate is cooled in ice to form crystals. Step 4: The crystals are collected by filtration, washed with cold water and left to dry. Explain the purpose of each underlined point. Minimum volume Hot water.... Filtered hot Cooled in ice Washed with cold water (Total 5 marks) 5 Salicylic acid, C 6 H 4 (OH)COOH, reacts with magnesium to produce magnesium salicylate and hydrogen. Complete the equation for this reaction. C 6 H 4 (OH)COOH () Page 5 of 80

6 (b) In an alternative method for determining percentage purity, a student reacted a solution of salicylic acid with an excess of magnesium and collected the hydrogen gas that was released. Complete the diagram below to show an apparatus that could be used to collect and measure the volume of hydrogen gas produced. () (Total 2 marks) 6 An experiment was carried out to determine the original concentration of iron(ii) ions in a solution that had been stored in air. An excess of zinc and acid was added to this solution. The mixture was then filtered to remove the excess zinc before titration. Suggest why the zinc and acid were added. () (b) Explain why it was necessary to remove the excess zinc. () (Total 2 marks) Page 6 of 80

7 7 The iron(ii) ions in well-water can be removed by oxidation using potassium manganate(vii) in alkaline solution. A mixture containing solid iron(iii) hydroxide and solid manganese(iv) oxide is formed. These solid products can be removed by filtration under reduced pressure. (i) Draw a diagram of the apparatus used for this filtration. Do not include the apparatus used to reduce the pressure. (2) (ii) An equation representing the oxidation reaction is given below. 3Fe 2+ (aq) + KMnO 4 (aq) + 5OH (aq) + 2H 2 O(I) 3Fe(OH) 3 (s) + MnO 2 (s) + K + (aq) Calculate the mass, in grams, of KMnO 4 required to react with the iron(ii) ions in.00 dm 3 of well-water that has an iron(ii) concentration of mol dm 3. Give your answer to the appropriate precision. Show your working. (3) (iii) In practice, a slight excess of potassium manganate(vii) is used to treat the well-water. Although this treated water is safe to drink, this excess of potassium manganate(vii) is undesirable. Suggest one reason, other than colour, why the excess is undesirable. () Page 7 of 80

8 (b) Suggest one reason why the colour of potassium manganate(vii) solution can be a source of error when using a volumetric (graduated) flask to prepare a standard solution. () (Total 7 marks) 8 When using potassium manganate(vii) in redox titrations with iron(ii) ions it is essential that the reaction mixture is acidified. Normally, dilute sulfuric acid is used. State why an excess of hydrogen ions is added to the reaction mixture. () (b) State why the acid used must not be ethanoic acid. () (c) Explain why an indicator is not needed in this redox titration. () (Total 3 marks) 9 A student prepared a sample of aspirin (melting point 35 C) in the laboratory and attempted to purify it by recrystallisation. To check the purity of the aspirin the student determined its melting point. State two observations, during this melting point determination, that would indicate that the sample is not pure. Observation... Observation 2... (2) Page 8 of 80

9 (b) Suggest why a pure sample of aspirin may sometimes appear to melt at a temperature different from 35 C. () (Total 3 marks) 0 Some scientists thought that the waste water from a waste disposal factory contained two sodium halides. They tested a sample of the waste water. They added three reagents, one after the other, to the same test tube containing the waste water. The table below shows their results. Reagent added. Silver nitrate solution (acidified with dilute nitric acid) Observations A cream precipitate formed 2. Dilute ammonia solution A yellow precipitate remained 3. Concentrated ammonia solution The yellow precipitate did not dissolve (i) Identify the yellow precipitate that did not dissolve in concentrated ammonia solution. Write the simplest ionic equation for the formation of this precipitate from silver ions and the correct halide ion. Identify the other sodium halide that must be present in this mixture of two sodium halides (3) (ii) Give one reason why the silver nitrate solution was acidified before it was used in this test () Page 9 of 80

10 (iii) The method that the scientists used could not detect one type of halide ion. Identify this halide ion. Give one reason for your answer (2) (b) The scientists thought that the waste water also contained dissolved barium ions. An aqueous solution of sodium sulfate can be used to test for the presence of dissolved barium ions. Write the simplest ionic equation for the reaction between barium ions and sulfate ions to form barium sulfate. State what is observed in this reaction. Give a use for barium sulfate in medicine and explain why this use is possible, given that solutions containing barium ions are poisonous (4) Page 0 of 80

11 (c) The scientists also analysed the exhaust gases from an incinerator used to destroy waste poly(ethene). Mass spectrometry showed that there was a trace gas with a precise M r = in the exhaust gases from the incinerator. The table below contains some precise relative atomic mass data. Atom Precise relative atomic mass 2 C H O Use the data to show that the trace gas is ethene. Show your working. Suggest why both ethene and carbon monoxide might have been identified as the trace gas if the scientists had used relative atomic masses to a precision of only one decimal place. Write an equation for the incomplete combustion of ethene to form carbon monoxide and water only. Ethene is used to make poly(ethene). Draw the displayed formula for the repeating unit of poly(ethene). Name this type of polymer (5) (Total 5 marks) Page of 80

12 Copper(II) sulfate solution, together with copper(ii) carbonate (CuCO 3 ) powder, can be used to determine the identity of three solutions A, B and C. The three solutions are known to be hydrochloric acid, barium chloride, and sodium chloride. In Experiment a small amount of copper(ii) carbonate powder was added to each of the three solutions. In Experiment 2 a dropping pipette was used to add 2 cm 3 of copper(ii) sulfate solution to each of the three solutions. The results of these experiments are shown in the table below. Experiment Addition of copper(ii) carbonate powder Experiment 2 Addition of copper(ii) sulfate solution Solution A no visible change white precipitate Solution B no visible change no visible change Solution C effervescence (bubbles of gas) no visible change Use the observations in the table to deduce which of the solutions, A, B or C is hydrochloric acid... barium chloride... (2) (b) Explain why a precipitate was formed when copper(ii) sulfate solution was added to solution A. Write an equation for the reaction that occurred. Explanation... Equation... (2) (c) Suggest the identity for the colourless gas produced when copper(ii) carbonate powder was added to solution C. () Page 2 of 80

13 (d) Identify the two reagents that could be used in a test to confirm that the solutions contained chloride ions, not bromide ions. State what would be observed on addition of each reagent. Reagent... Observation... Reagent 2... Observation 2... (4) (e) Copper(II) sulfate is toxic. Suggest one safety precaution you would take to minimise this hazard when wiping up a spillage of copper(ii) sulfate solution. () (Total 0 marks) 2 A solution of barium hydroxide is often used for the titration of organic acids. A suitable indicator for the titration is thymol blue. Thymol blue is yellow in acid and blue in alkali. In a titration a solution of an organic acid was added from a burette to a conical flask containing 25.0 cm 3 of a barium hydroxide solution and a few drops of thymol blue. (i) Describe in full the colour change at the end-point of this titration. () (ii) Thymol blue is an acid. State how the average titre would change if a few cm 3, rather than a few drops, of the indicator were used by mistake in this titration. () (iii) Barium hydroxide is toxic. Suggest one safety precaution you would take to minimise this hazard when wiping up a spillage of barium hydroxide solution. () (iv) Suggest one reason why a 250 cm 3 conical flask is preferred to a 250cm 3 beaker for a titration. () Page 3 of 80

14 (v) Suggest one reason why repeating a titration can improve its reliability () (b) Solubility data for barium hydroxide and calcium hydroxide are given in the table below. Compound Solubility at 20 C / g dm 3 barium hydroxide 38.9 calcium hydroxide.73 (i) Use the data given in the table to calculate the concentration, in mol dm 3, of a saturated solution of calcium hydroxide (M r = 74.) at 20 C. () (ii) Suggest one reason why calcium hydroxide solution is not used in the titration of a mol dm 3 solution of an acid. () (Total 7 marks) 3 In an experiment to determine its solubility in water, solid barium hydroxide was added to 00cm 3 of water until there was an excess of the solid. The mixture was filtered and an excess of sulfuric acid was added to the filtrate. The barium sulfate produced was obtained from the reaction mixture, washed with cold water and dried. The mass of barium sulfate was then recorded. Explain why the mixture was filtered before the addition of sulfuric acid. () (b) State how the barium sulfate produced was obtained from the reaction mixture. () Page 4 of 80

15 (c) Explain why the barium sulfate was washed before it was dried. () (d) Write an equation for the reaction between barium hydroxide and sulfuric acid. () (e) In an experiment, 4.25 g of barium sulfate were formed when an excess of sulfuric acid was added to 00 cm 3 of a saturated solution of barium hydroxide. (i) Use data from the Periodic Table to calculate the M r of barium sulfate. Give your answer to one decimal place. () (ii) Calculate the amount, in moles, of BaSO 4 in 4.25 g of barium sulfate. () (iii) Use your answer from part (ii) to calculate the mass of barium hydroxide (M r = 7.3) present in dm 3 of saturated solution. Show your working. (2) (f) Barium sulfate is taken by mouth by patients so that an outline of a human digestive system can be viewed using X-rays. Explain why patients do not suffer any adverse effects from barium sulfate when it is known that solutions containing barium ions are toxic. () (Total 9 marks) Page 5 of 80

16 4 A chemist was asked to prepare a standard solution of sodium carbonate. The chemist dissolved an accurately known mass of sodium carbonate in a small amount of water in a conical flask. The chemist then poured the solution into a 250 cm 3 graduated flask and made the solution up to the mark. Suggest one improvement to the chemist s procedure (Total mark) 5 Propanoic acid can be made from propan--ol by oxidation using acidified potassium dichromate(vi). Propanal is formed as an intermediate during this oxidation. (i) State the colour of the chromium species after the potassium dichromate(vi) has reacted. () (ii) Describe the experimental conditions and the practical method used to ensure that the acid is obtained in a high yield. Draw a diagram of the assembled apparatus you would use. Conditions... Apparatus (4) (iii) Describe the different experimental conditions necessary to produce propanal in high yield rather than propanoic acid. (2) Page 6 of 80

17 (b) Propan--ol is a volatile, flammable liquid. Give one safety precaution that should be used during the reaction to minimise this hazard. () (c) A student followed the progress of the oxidation of propan--ol to propanoic acid by extracting the organic compounds from one sample of reaction mixture. (i) Give a chemical reagent which would enable the student to confirm the presence of propanal in the extracted compounds. State what you would observe when propanal reacts with this reagent. Reagent... Observation (2) (ii) Give a chemical reagent that would enable the student to confirm the presence of propanoic acid in the extracted compounds. State what you would observe when propanoic acid reacts with this reagent. Reagent... Observation (2) (d) Predict which one of the compounds, propan--ol, propanal and propanoic acid will have the highest boiling point. Explain your answer. Prediction... Explanation (3) (Total 5 marks) 6 Steel rods are cleaned before they are painted. The rods are cleaned by passing them through a bath of dilute sulfuric acid. This process produces large quantities of iron(ii) sulfate. Write an equation for the reaction between iron and dilute sulfuric acid. () Page 7 of 80

18 (b) State one chemical hazard in this process and suggest an appropriate safety precaution for this hazard. Hazard... Precaution... (2) (Total 3 marks) 7 The concentration of iron(iii) ions in a dilute solution can be determined by visible spectrometry. The absorption of light of a particular frequency by solutions of iron(iii) sulfate of different concentrations was measured. The results are shown in the table below. Percentage absorbance Concentration of iron(iii) sulfate / mol dm Page 8 of 80

19 Use these results to plot a graph of percentage absorbance (y-axis) against concentration of iron(iii) sulfate on the grid below. Draw a straight line of best fit. (2) (b) Use your graph to determine the concentration of an iron(iii) sulfate solution that has a percentage absorbance of 4.0%. () (Total 3 marks) 8 State why it is necessary to maintain a constant temperature in an experiment to measure an equilibrium constant. () Page 9 of 80

20 (b) Suggest one method for maintaining a constant temperature in an experiment. () (Total 2 marks) 9 Samples of -chloropropane and ethanoyl chloride can be distinguished by the addition of an aqueous solution of silver nitrate. State what you would observe with each sample. Observation with -chloropropane Observation with ethanoyl chloride (Total 2 marks) 20 The following pairs of compounds can be distinguished by observing what happens in test-tube reactions. For each pair, give a suitable aqueous reagent that could be added separately to each compound. Describe what you would observe in each case. NaF(aq) and NaCl(aq) Reagent... Observation with NaF(aq)... Observation with NaCl(aq)... (3) (b) BaCl 2 (aq) and MgCl 2 (aq) Reagent... Observation with BaCl 2 (aq)... Observation with MgCl 2 (aq)... (3) (c) AgCl(s) and AgI(s) Reagent... Observation with AgCl(s)... Observation with AgI(s)... (3) Page 20 of 80

21 (d) Butan-2-ol(l) and 2-methylpropan-2-ol(l) Reagent... Observation with butan-2-ol(l)... Observation with 2-methylpropan-2-ol(l)... (3) (Total 2 marks) 2 Aqueous metal ions can be identified by test-tube reactions. For each of the following, describe what you would observe. Write an equation or equations for any reactions that occur. The addition of aqueous sodium carbonate to a solution containing [Fe(H 2 O) 6 ] 3+ (aq) ions (4) (b) The addition of aqueous sodium hydroxide, dropwise until in excess, to a solution containing [Al(H 2 O) 6 ] 3+ (aq) ions (4) Page 2 of 80

22 (c) The addition of dilute aqueous ammonia, dropwise until in excess, to a solution containing [Cu(H 2 O) 6 ] 2+ (aq) ions (4) (d) The addition of concentrated hydrochloric acid, dropwise until in excess, to a solution containing [Cu(H 2 O) 6 ] 2+ (aq) ions (2) (Total 4 marks) 22 Ammonium salts such as ammonium nitrate are used in fertilisers. The ammonium nitrate content of a fertiliser can be determined by heating a sample of the fertiliser with an excess of sodium hydroxide solution. An equation for this reaction is shown below. NH 4 NO 3 + NaOH NH 3 + NaNO 3 + H 2 O Heating ensures that all of the ammonia produced is given off as a gas. The unreacted sodium hydroxide remaining in the solution can be determined by a titration with standard hydrochloric acid. Explain why it is necessary to remove all of the ammonia before titrating the unreacted sodium hydroxide. () Page 22 of 80

23 (b) Suggest why it is important to test samples from more than one batch of the fertiliser. () (c) Ammonium nitrate decomposes when heated to form water and one other product. Write an equation for this reaction. () (d) The table below shows some information about three salts that could be used in fertilisers. Salt Nitrogen content by mass / % Price per tonne / Ammonium chloride Ammonium nitrate Ammonium sulfate 2.2 (i) Use the data in the table to determine the salt that offers the best value for money, based on nitrogen content. Show your working. (2) (ii) Ammonium nitrate is very soluble in water. Suggest one disadvantage of its high solubility when ammonium nitrate is used in a fertiliser. () (e) A saturated solution of ammonia contains 300 g of ammonia in.00 dm 3 of solution. Calculate the concentration, in mol dm 3, of ammonia in this solution. () (Total 7 marks) Page 23 of 80

24 23 In an experiment to determine the concentration of a solution of sodium hydroxide, 25.0 cm 3 of 0.00 mol dm 3 hydrochloric acid were transferred to a conical flask. An indicator was added to the flask. The solution of sodium hydroxide was then added to the flask from a burette. State a suitable amount of indicator solution that should be added to the flask. () (b) State why it is important to fill the space below the tap in the burette with alkali before beginning the titration. () (Total 2 marks) 24 An equation for the decomposition of hydrogen peroxide is shown below. 2H 2 O 2 2H 2 O + O 2 State the measurements you would take in order to investigate the rate of this reaction (Total 2 marks) 25 Ethanol can be oxidised slowly to ethanal. State how a sample of ethanol could be tested to confirm the presence of ethanal. State what you would observe. Test. Observation... (Total 2 marks) Page 24 of 80

25 26 The scheme below shows some reactions of copper(ii) ions in aqueous solution. W, X, Y and Z are all copper-containing species. Identify ion W. Describe its appearance and write an equation for its formation from [Cu(H 2 O) 6 ] 2+ (aq) ions. Ion W... Appearance... Equation... (3) (b) Identify compound X. Describe its appearance and write an equation for its formation from [Cu(H 2 O) 6 ] 2+ (aq) ions. Compound X... Appearance... Equation... (3) (c) Identify ion Y. Describe its appearance and write an equation for its formation from X. Ion Y... Appearance... Equation... (3) Page 25 of 80

26 (d) Identify compound Z. Describe its appearance and write an equation for its formation from [Cu(H 2 O) 6 ] 2+ (aq) ions. Compound Z... Appearance... Equation... (3) (e) Copper metal can be extracted from a dilute aqueous solution containing copper(ii) ions using scrap iron. (i) Write an equation for this reaction and give the colours of the initial and final aqueous solutions. Equation... Initial colour... Final colour... (3) (ii) This method of copper extraction uses scrap iron. Give two other reasons why this method of copper extraction is more environmentally friendly than reduction of copper oxide by carbon. Reason... Reason 2... (2) (Total 7 marks) Page 26 of 80

27 27 Ethanoic acid is manufactured in industry from methanol and carbon monoxide in a multi-step process involving hydrogen iodide. Ethanoic acid is obtained from the reaction mixture by fractional distillation. Methanoic acid is a useful by-product of this process. The K a value of an organic acid can be determined by using the ph curve obtained when the acid is titrated against sodium hydroxide. The ph of the solution formed when exactly half of the acid has been neutralised is equal to the pk a value of the acid. The K a value of the acid can be used to confirm its identity. A chemist used a ph curve to determine the pk a value of acid Y, formed during the manufacture of ethanoic acid. The chemist transferred 25.0 cm 3 of a solution of acid Y into a beaker using a pipette, and measured the ph of the acid solution using a ph meter which could be read to one decimal place. A solution of sodium hydroxide of concentration 0.00 mol dm 3 was added from a burette in small portions. The ph of the mixture was recorded after each addition of the sodium hydroxide solution. The chemist s results are given in the table below. Volume of sodium hydroxide solution added / cm 3 ph Volume of sodium hydroxide solution added / cm 3 ph Page 27 of 80

28 Use the results given in the table above to plot a graph of ph (y-axis) against volume of sodium hydroxide solution added. Use the points to draw the ph curve, ignoring any anomalous results. (6) Page 28 of 80

29 (b) Use your graph from part to determine the (i) volume of sodium hydroxide solution at the end-point of the titration... cm 3 (ii) volume of sodium hydroxide solution needed to neutralise half the acid... cm 3 (iii) ph of the half-neutralised mixture. Give your answer to one decimal place.... (3) (c) Use the ph of the half-neutralised mixture from part (b) (iii) to calculate the value of the acid dissociation constant, K a, of the acid Y. Show your working. (2) (d) The table below shows the K a values for some organic acids. Acid K a / mol dm 3 Methanoic acid Ethanoic acid Iodoethanoic acid Propanoic acid Use your answer from part (c) to identify acid Y from this table. () Page 29 of 80

30 (e) For the pipette and the burette, the maximum total errors are shown below. These errors take into account multiple measurements. pipette burette ± 0.05 cm 3 ± 0.5 cm 3 Estimate the percentage error in using each of these pieces of apparatus. You should use your answer to part (b) (i) to estimate the percentage error in using the burette. () (f) Calculate the difference between the K a value from part (c) and the K a value of the acid you identified as the acid Y in the table in part (d). Express this difference as a percentage of the value given in the table in part (d). (If you could not complete the calculation in part (c), you should assume that the K a value determined from the graph is mol dm 3. This is not the correct value.) () (g) Other than by using a different ph meter, state one way in which the accuracy of the ph readings could be improved. () (h) State why there was little change in the ph value of the mixture when between 8 cm 3 and 20 cm 3 of alkali were added. () (Total 6 marks) Page 30 of 80

31 28 When a solution containing iron(ii) ions is treated with a slight excess of a solution containing ethanedioate ions a bright yellow precipitate of hydrated iron(ii) ethanedioate, FeC 2 O 4.2H 2 O, is formed. The precipitate is filtered off, washed with propanone and then allowed to dry. A typical yield of the solid is 95%. (i) Propanone boils at 56 C and is miscible with water in all proportions. Suggest two reasons why washing with propanone is an effective method for producing a pure, dry precipitate. Reason... Reason 2... (2) (ii) By suggesting a simple test tube reaction, state how the filtrate could be tested to show that all of the iron(ii) ions have been removed from the solution. State what you would observe. Test... Observation... (2) (iii) Suggest one reason why the typical yield of iron(ii) ethanedioate is less than 00%. () (iv) Calculate the mass of hydrated iron(ii) ethanedioate, FeC 2 O 4.2H 2 O that can be formed from 50.0 cm 3 of a 0.50 mol dm 3 solution of iron(ii) sulfate when the yield of the reaction is 95%. Show your working. (3) Page 3 of 80

32 (v) The identity of the precipitate can be confirmed by dissolving it in sulfuric acid and titrating the mixture with potassium manganate(vii). Deduce the number of moles of iron(ii) ethanedioate that would react with one mole of potassium manganate(vii) in acidic solution. () (b) Ethanedioate ions can be used to remove calcium ions from blood plasma. A precipitate of calcium ethanedioate is formed. Write an ionic equation for the reaction of ethanedioate ions with calcium ions. () (c) Ethanedioic acid is used to clean marble, a form of calcium carbonate. Suggest one reason why the reaction between ethanedioic acid and marble stops after a short time. () (d) Tea leaves contain ethanedioic acid. Suggest one reason why tea drinkers do not suffer from ethanedioic acid poisoning. () (e) Ethanedioic acid is produced by the oxidation of carbon monoxide in a multi-step process. The equation which summarises the reactions taking place is shown below. 4CO + 4NaOH + O 2 + 4HCl 2H 2 C 2 O 4 + 4NaCl + 2H 2 O Calculate the percentage atom economy for the formation of ethanedioic acid in this reaction. Show your working. (2) (Total 4 marks) Page 32 of 80

33 29 Hydrogen peroxide is a powerful oxidising agent. Acidified hydrogen peroxide reacts with iodide ions to form iodine according to the following equation. H 2 O 2 (aq) + 2H + (aq) + 2I (aq) I 2 (aq) + 2H 2 O(l) The initial rate of this reaction is investigated by measuring the time taken to produce sufficient iodine to give a blue colour with starch solution. A series of experiments was carried out, in which the concentration of iodide ions was varied, while keeping the concentrations of all of the other reagents the same. In each experiment the time taken (t) for the reaction mixture to turn blue was recorded. The initial rate of the reaction can be represented as ( ), and the initial concentration of iodide ions can be represented by the volume of potassium iodide solution used. A graph of log 0 ( ) on the y-axis against log 0 (volume of KI(aq)) is a straight line. The gradient of this straight line is equal to the order of the reaction with respect to iodide ions. The results obtained are given in the table below. The time taken for each mixture to turn blue was recorded on a stopclock graduated in seconds. Expt. Volume of KI(aq) / cm 3 log 0 (volume of KI(aq)) Time / s log 0 ( ) Page 33 of 80

34 Use the results given in the table to plot a graph of log 0 ( ) on the y-axis against log 0 (volume of KI(aq)). Draw a straight line of best fit on the graph, ignoring any anomalous points. (5) Page 34 of 80

35 (b) Determine the gradient of the line you have drawn. Give your answer to two decimal places. Show your working. (3) (c) Deduce the order of reaction with respect to iodide ions. () (d) A student carried out the experiment using a flask on the laboratory bench. The student recorded the time taken for the reaction mixture to turn blue. State one way this method could be improved, other than by repeating the experiment or by improving the precision of time or volume measurements. Explain why the accuracy of the experiment would be improved. Improvement... Explanation... (2) (Total marks) 30 Pure hydrogen peroxide is a colourless liquid with a boiling point of 50 C. Hydrogen peroxide was originally produced commercially in a two-stage process. In the first stage barium was heated in air to form barium peroxide. In the second stage barium peroxide was added to aqueous nitric acid. The equations for the reactions are shown below. Stage Ba(s) + O 2 (g) BaO 2 (s) Stage 2 BaO 2 (s) + 2HNO 3 (aq) H 2 O 2 (aq) + Ba(NO 3 ) 2 (aq)2 Suggest one method of separating hydrogen peroxide from the reaction mixture in Stage 2. () (b) Apart from cost, suggest one reason why nitric acid was eventually replaced by sulfuric acid in Stage 2. () Page 35 of 80

36 (c) Suggest one reason why infrared spectroscopy could not be used to indicate the presence of a small amount of water in hydrogen peroxide. () (Total 3 marks) 3 Ethanal is prepared by heating ethanol with potassium dichromate(vi) in the presence of sulfuric acid. Figures and 2 show two possible ways of heating this reaction mixture. Figure Figure 2 State which arrangement would not be suitable for the preparation of ethanal. Explain your answer. Arrangement... Explanation (Total 2 marks) Page 36 of 80

37 32 Describe briefly how you would ensure that a reading from a ph meter is accurate (Total 2 marks) 33 Describe briefly how you could measure the melting point of aspirin (Total 2 marks) 34 Some antacid tablets contain sodium hydrogencarbonate, sucrose and citric acid. Analysis of a pure sample of citric acid showed that it contained 37.50% of carbon and 4.7% of hydrogen by mass, the remainder being oxygen. Use these data to show that the empirical formula of the acid is C 6 H 8 O 7. (3) (b) When the antacid tablet is added to water, sodium hydrogencarbonate and citric acid react together to form a gas. Identify this gas. () Page 37 of 80

38 (c) A weighed portion of this antacid was added to water. The gas formed was collected and its volume measured. (i) Draw a diagram to show how this experiment could have been carried out to collect and measure the volume of the gas. (ii) The experiment was repeated with further weighed portions of the same antacid. The results are shown below. Experiment Mass of antacid / g Volume of gas collected / cm Page 38 of 80

39 On the graph paper below, plot a graph of mass of antacid (x-axis) against volume of gas collected. (3) 2 Draw a line of best fit on the graph, ignoring any anomalous points. () Page 39 of 80

40 3 Use the graph to determine the volume of gas which would have been collected using 2.00 g of antacid. Volume of gas collected... () (d) Suggest one reason why the presence of sodium hydrogencarbonate in the stomach may cause a person to suffer some extra discomfort for a short time. () (e) Explain why the value for the M r of citric acid does not need to be an exact value to deduce the molecular formula of citric acid from its empirical formula. (2) (f) Apart from misreading the gas volume, suggest two reasons why the volumes of gas collected may be lower than the volumes of gas produced. Reason... Reason 2... (2) (g) Explain why it is important to record the temperature and pressure when measuring the volume of a gas. () (h) Suggest why, in an analysis of an antacid, it is important to test samples from more than one bottle of the antacid. () Page 40 of 80

41 (i) In the industrial production of sodium hydrogencarbonate, ammonia and carbon dioxide are bubbled through a saturated solution of sodium chloride. The equation for this reaction, and some solubility data, are shown below. NaCl(aq) + NH 3 (aq) + CO 2 (g) + H 2 O(l) NaHCO 3 (s) + NH 4 Cl(aq) Compound Solubility in water at 20 C / g dm 3 sodium chloride 360 sodium hydrogencarbonate 96 ammonium chloride 370 (i) Suggest one reason why sodium hydrogencarbonate precipitates from the reaction mixture at this temperature. () (ii) Explain how this reaction could be used to remove carbon dioxide from the gases formed when fossil fuels are burned. () (j) The thermal decomposition of sodium hydrogencarbonate produces sodium carbonate. The other products are water and carbon dioxide. Write an equation for this thermal decomposition. () (k) Sodium carbonate is produced on an industrial scale by a multi-step process. The equation which summarises the reactions taking place is shown below. CaCO 3 + 2NaCl CaCl 2 + Na 2 CO 3 Calculate the percentage atom economy for the production of sodium carbonate by this reaction. () (Total 20 marks) Page 4 of 80

42 35 A chemical company s records refer to the following acids hydrochloric acid hydrobromic acid hydriodic acid nitric acid sulfuric acid A waste tank was thought to contain a mixture of two of these acids. A chemist performed test-tube reactions on separate samples from the waste tank. The results of these tests are shown below. Test Reagent Observations A Barium chloride solution White precipitate B Silver nitrate solution White precipitate Use the result from Test A to identify an acid in the company s records which must be present in the waste tank. () (b) Use the results from Test A and Test B to identify an acid in the company s records which must be absent from the waste tank. () (c) The chemist suspected that the waste tank contained hydrochloric acid. State how the precipitate formed in Test B could be tested to confirm the presence of hydrochloric acid in the waste tank. State what you would observe. Test. Observation... (2) (d) Suggest one reason why carbonate ions could not be present in the waste tank. () (Total 5 marks) Page 42 of 80

43 36 Magnesium carbonate, MgCO 3, can occur as the anhydrous compound, or as hydrates with 2, 3 or 5 molecules of water of crystallisation. All types of magnesium carbonate can be decomposed to form magnesium oxide, an important starting material for many processes. This decomposition reaction can be used to identify the type of magnesium carbonate present in a mineral. A chemist was asked to identify the type of magnesium carbonate present in a mineral imported from France. The chemist weighed a clean dry crucible, and transferred 0.25 g of the magnesium carbonate mineral to the crucible. The crucible was then heated for a few minutes. The crucible was then allowed to cool, and the crucible and its contents were reweighed. This process was repeated until the crucible and its contents had reached constant mass. The mass of the crucible and its contents was then recorded. The experiment was repeated using different masses of the magnesium carbonate mineral. For each experiment the chemist recorded the original mass of the mineral and the mass of magnesium oxide left after heating to constant mass. The chemist s results are shown in the table below. Experiment Mass of mineral / g Mass of magnesium oxide / g Page 43 of 80

44 Plot a graph of the mass of the mineral (x-axis) against the mass of magnesium oxide on the grid below. Draw a straight line of best fit on your graph. (4) (b) Use the graph to determine the mass of the mineral which would have formed 0.50 g of magnesium oxide. Mass of the mineral... () Page 44 of 80

45 (c) Calculate the amount, in moles, of MgO present in 0.50 g of magnesium oxide. () (d) Use your answers from part (b) and from part (c) to calculate the M r of the magnesium carbonate present in the mineral. () (e) Use your answer from part (d) to confirm that this mineral is MgCO 3.2H 2 O (If you could not complete the calculation in part (d), you should assume that the experimental M r value is 22.0 This is not the correct answer.) () (f) Explain why it was not necessary to use a more precise balance in this experiment. () (g) Consider your graph and comment on the results obtained by the chemist. Identify any anomalous results. Comment... Anomalous results... (2) (h) Explain why it was necessary for the chemist to heat the crucible and its contents to constant mass. () Page 45 of 80

46 (i) Suggest one reason in each case why (i) small amounts of the mineral, such as 0.0 g, should not be used in this experiment. () (ii) large amounts of the mineral, such as 50 g, should not be used in this experiment. () (j) Analysis of a different hydrated magnesium carbonate showed that it contained 39.05% by mass of water. Determine the formula of this hydrated magnesium carbonate. (2) (k) Magnesium oxide is produced by the thermal decomposition of magnesium carbonate and by the thermal decomposition of magnesium hydroxide. The equations for the reactions taking place are shown below. Reaction Reaction 2 MgCO 3 Mg(OH) 2 MgO + CO 2 MgO + H 2 O Show that Reaction 2 has the greater atom economy for the production of magnesium oxide. (2) (l) Apart from cost, suggest one advantage of using magnesium hydroxide rather than magnesium carbonate to reduce acidity in the stomach. () (Total 9 marks) Page 46 of 80

47 37 In an experiment to determine the rate of a reaction, the volume of gas produced in the reaction was measured at regular intervals for several minutes. State one experimental condition that must be kept constant during the experiment. () (b) Describe how the initial rate of this reaction can be determined from a graph of volume of gas produced against time. () (Total 2 marks) 38 Both strontium carbonate and strontium sulfate are white solids which are insoluble in water. Strontium carbonate reacts with hydrochloric acid to produce a solution of strontium chloride. Strontium sulfate does not react with hydrochloric acid. Describe how you would obtain strontium sulfate from a mixture of strontium carbonate and strontium sulfate (Total 2 marks) 39 In an investigation of the chemical properties of alcohols, a mixture of ethanol and acidified potassium dichromate(vi) is heated in a conical flask in a water bath. Explain why a water bath is used to heat the mixture. () (b) Describe the colour change which would be observed. () (Total 2 marks) Page 47 of 80

48 40 A chemist has discovered that the labels have fallen off four bottles each of which contains a different organic liquid. These liquids are known to be propan-2-ol, propanal, hexene and -bromopropane. Suggest a series of test-tube reactions which a chemist could use to confirm the identities of the four compounds. State the reagents used and the observations expected. (Total 0 marks) 4 When aqueous ammonia was added to an aqueous solution of cobalt(ii) sulfate, a blue precipitate M was formed. Identify the cobalt-containing species present in aqueous cobalt(ii) sulphate and in the precipitate M. Cobalt-containing species... Precipitate M... (2) (b) Precipitate M dissolved when an excess of concentrated aqueous ammonia was added. The solution formed was pale brown due to the presence of the cobalt-containing species P. Identify P.... () (c) On standing in air, the colour of the solution containing P slowly darkened as the cobaltcontaining species Q was formed. State the type of reaction occurring when P changes into Q and identify the reactant responsible for this change. Type of reaction... Reactant responsible... (2) (d) When potassium iodide was added to the solution containing Q and the mixture was acidified, a dark brown solution due to the presence of R was formed. On addition of starch solution the mixture turned blue-black. Identify R and explain its formation. Identity of R... Explanation... (2) (Total 7 marks) Page 48 of 80

49 42 State the trend in the boiling points of the halogens from fluorine to iodine and explain this trend. Trend... Explanation (4) (b) Each of the following reactions may be used to identify bromide ions. For each reaction, state what you would observe and, where indicated, write an appropriate equation. (i) The reaction of aqueous bromide ions with chlorine gas Observation... Equation... (ii) The reaction of aqueous bromide ions with aqueous silver nitrate followed by the addition of concentrated aqueous ammonia Observation with aqueous silver nitrate... Equation... Observation with concentrated aqueous ammonia (iii) The reaction of solid potassium bromide with concentrated sulphuric acid Observation... Observation 2... (7) (c) Write an equation for the redox reaction that occurs when potassium bromide reacts with concentrated sulphuric acid.... (2) (Total 3 marks) Page 49 of 80

50 W is [Co(NH 3 ) 6 ] 2+ Mark schemes To prevent vigorous boiling / uneven boiling / bubbling vigorously Reference to an effect on reaction here loses this mark. (b) Condenser Accept condensation chamber or condensation tube. Should show effective water jacket and central tube If a flask is also drawn then the condenser must be at an appropriate angle. Apparatus must clearly work. Ignore direction of water flow. Diagram must have a clear flow of vapour and water eg unblocked central tube or flow indicated by arrows. [3] 2 (Mix the alcohol with warm) K 2 Cr 2 O 7 / H + allows 3 identification by lack of reaction Scheme must allow the alcohol to be distinguished to get all marks. Distillation of initial product needed for / 2 If distillation stage not clear then max. 2 (M and M3). Awareness of correct reactions / lack of reaction relating to each class of alcohol is worth mark. Effect of Tollens / Fehling s on oxidation product to identify or 2 (by default) Reacting Tollens / Fehling s with alcohols directly is incorrect and gains no M2 or M3. Detailed observations relating to the reactions are not needed but should be penalised where incorrect. [3] 3 For reactions to 3 must show complex ions as reactants and products Take care to look for possible identification on flow chart Reaction ammonia solution [Co(H 2 O) 6 ] NH 3 [Co(NH 3 ) 6 ] H 2 O Correct equation scores all 3 marks Page 50 of 80

51 H 2 O 2 X is [Co(NH 3 ) 6 ] 3+ Y is [CoCl 4 ] 2- Z is CoCO 3 Co(OH) 2 /Co(H 2 O) 4 (OH) 2 Allow Co 2+ + CO 3 2- CoCO 3 Reaction 2 Allow oxygen, Do not allow air 2[Co(NH 3 ) 6 ] 2+ + H 2 O 2 2[Co(NH 3 ) 6 ] OH Allow 2[Co(NH 3 ) 6 ] 2+ + ½O 2 + H 2 O 2[Co(NH 3 ) 6 ] OH Correct equations score all 3 marks Reaction 3 HCl Do not allow Cl but mark on [Co(H 2 O) 6 ] Cl [CoCl 4 ] H 2 O/ Correct equation scores previous mark [Co(H 2 O) 6 ] HCl [CoCl 4 ] H 2 O + 4H + This equation scores all three marks Reaction 4 Na 2 CO 3 Or NaOH/NH 3 Do not allow CaCO 3 as a reagent but mark on [Co(H 2 O) 6 ] 2+ + CO 3 2- CoCO 3 + 6H 2 O [Co(H 2 O) 6 ] OH Co(H 2 O) 4 (OH) 2 + 2H 2 O etc Allow waters to stay co-ordinated to Co. This mark also previous mark Or [Co(H 2 O) 6 ] 2+ + Na 2 CO 3 CoCO 3 + 6H 2 O + 2Na + Page 5 of 80

52 ½O 2 + 2Co H + H 2 O + 2Co 3+ (b) SO ½O 2 SO 4 2- Allow multiples The activation energy is lower (for the catalysed route) Or Co 3+ attracts SO 3 2- /Co 2+ attracts SO 3 2- /oppositely charged ions attract 2Co 3+ + SO H 2 O 2Co 2+ + SO H + Allow these equations in either order [6] 4 Minimum volume and hot water: Note that this question is worth a total of 5 marks. Any two from: to obtain saturated solution to increase yield / reduce amount left in solution enable crystallisation (on cooling) Do not allow because acid doesn t dissolve well in cold water. Filtered hot: to remove insoluble impurities / to prevent crystals forming during filtration Cooled in ice: to increase amount of crystals that are formed Do not allow to cool quickly. Washed with cold water: to remove soluble impurities Allow washing with hot water would dissolve some of the crystals. Max 2 [5] 5 Mg + 2C 6 H 4 (OH)COOH (C 6 H 4 (OH)COO) 2 Mg + H 2 Accept multiples, including fractions. Page 52 of 80

53 (b) Gas syringe / inverted burette over water / measuring cylinder over water Collection apparatus must show graduations or be clearly labelled (eg syringe, burette, measuring cylinder). [2] 6 To reduce any Fe 3+ ions to Fe 2+ ions Allow to ensure that all of the iron present is in the form of Fe 2+ ions or to ensure that no Fe 3+ ions are present. (b) Zinc would react with MnO 4 / Fe 3+ produced in titration Do not allow would increase titre value. Do not allow zinc would react without further qualification. [2] 7 (i) Flask with side arm Buchner funnel and horizontal filter paper Allow Hirsch funnel and horizontal filter paper. Do not allow standard Y-shaped funnel. If there is not a clear air-tight seal (labelled or drawn) between the funnel and the flask maximum mark. (ii) M r KMnO 4 = 58(.0) Mass = / 3 =.9 (g) Lose M2 if no working shown. Allow consequential mark on an incorrect M r for KMnO 4 (iii) Precision mark: three significant figures Allow if mass incorrect. (Unpleasant) taste Ignore smell. (b) Difficult to see meniscus / line on graduated flask Do not allow reference to over filling. [7] 8 Stop the formation of MnO 2 / Ensures all MnO 4 reacts to form Mn 2+ / becomes colourless (b) Weak acid / Does not supply sufficient H + Page 53 of 80

54 (c) It is self-indicating / Purple to colourless end-point or vice versa If colours mentioned they must be correct. [3] 9 Melting range would be wide (>3 deg C) / not sharp Allow melts over a range of temperatures. below / before the true m.p. Do not allow above or below. (b) Temperature on thermometer not the same as the sample Allow sample heats up at a different / higher / lower rate than thermometer. [3] 0 (i) M (yellow precipitate is) silver iodide OR AgI (which may be awarded from the equation) M2 Ag + + I AgI (Also scores M unless contradicted) M3 sodium chloride OR NaCl For M2 Accept multiples Ignore state symbols Allow crossed out nitrate ions, but penalise if not crossed out 3 (ii) The silver nitrate is acidified to react with / remove ions that would interfere with the test prevent the formation of other silver precipitates / insoluble silver compounds that would interfere with the test remove (other) ions that react with the silver nitrate react with / remove carbonate / hydroxide / sulfite (ions) Ignore reference to false positive Page 54 of 80

55 NOT It unless clearly BaSO 4 4 (iii) M and M2 in either order M Fluoride (ion) OR F M2 Silver fluoride / AgF is soluble / dissolves (in water) no precipitate would form / no visible /observable change Do not penalise the spelling fluoride, Penalise fluride once only Mark M and M2 independently 2 (b) M Ba SO 4 BaSO 4 (or the ions together) M2 white precipitate / white solid / white suspension M3 Barium meal or ( internal ) X-ray or to block X-rays M4 BaSO 4 / barium sulfate is insoluble (and therefore not toxic) For M, ignore state symbols Allow crossed out sodium ions, but penalise if not crossed out For M2, ignore milky If BaSO 3 OR BaS used in M and M4, penalise once only For M3 Ignore radio-tracing For M4 NOT barium ions NOT barium NOT barium meal (c) M 2( ) + 4(.00794) = M2 Ethene and CO or they have an imprecise M r of 28.0 / 28 OR Ethene and CO or they have the same M r to one d.p. OR These may be shown by two clear, simple sums identifying both compounds Page 55 of 80

56 M3 C 2 H 4 + 2O 2 2CO + 2H 2 O (H 2 C=CH 2 ) M4 Displayed formula M5 Type of polymer = Addition (polymer) M must show working using 5 d.p.for hydrogen Penalise similar or close to, if this refers to the imprecise value in M2, since this does not mean the same For M3, accept CH 2 =CH 2 OR CH 2 CH 2 For M4, all bonds must be drawn out including those on either side of the unit. Penalise sticks Ignore brackets around correct repeating unit but penalise n Penalise additional 5 [5] Hydrochloric acid = C Barium chloride = A (b) Barium sulfate is insoluble CuSO 4 + BaCl 2 BaSO 4 + CuCl 2 Accept multiples. Accept ionic equation. Do not penalise lack of state symbols, but if used they must be correct. (c) CO 2 / Carbon dioxide (d) Reagent silver nitrate (solution) Ignore lack of reference to acidifying prior to addition of silver nitrate solution. Page 56 of 80

57 (e) Observation White precipitate Reagent 2 (dilute) ammonia solution / aqueous ammonia Do not accept addition of ammonia only. Observation 2 (Colourless) solution Allow ppt dissolves. Do not allow goes colourless or goes clear. Chlorine and no visible change or solution does not become orange scores M3 and M4. Gloves / wash hands after use Ignore eye protection. Do not accept do not ingest the chemicals, wipe up spillages, use a fume cupboard, wear a lab coat (list principle). [0] 2 (i) Blue to green Accept blue to yellow. (ii) (iii) (iv) (v) Decrease / less acid needed Ignore references to rate Gloves or avoid skin contact Allow if reagent contacts skin wash off (immediately) or answers to that effect. Do not accept wash only. Ignore eye protection or lab coat or use of fume cupboard or don t ingest. Less chance of losing liquid on swirling / liquid doesn t splash on swirling Do not accept easier to swirl on its own. Do not accept easier to stir. Idea that a single titration could be flawed / anomalous Allow an indication that the first titration is a rough titration. Do not allow to improve accuracy without qualification. Do not allow vague references to outliers. (b) (i) 2.3(3) 0 2 Do not penalise additional significant figures, but do not allow 0.02 Page 57 of 80