CIE Nov 2017 v2 Paper 5 Q1

Answers available below

PMT Verdigris is a green pigment that contains both copper(II) carbonate, CuCO3, and copper(II) hydroxide, Cu(OH)2, in varying amounts. Both copper compounds react with dilute hydrochloric acid. CuCO3(s) + 2HCl (aq) CuCl 2(aq) + CO2(g) + H2O(l) Cu(OH)2(s) + 2HCl (aq) CuCl 2(aq) + 2H2O(l) (a) You are to plan an experiment to determine the percentage of copper(II) carbonate in a sample of verdigris. Your method should involve the reaction of verdigris with excess dilute hydrochloric acid. You are provided with the following materials.0.5 g of verdigris 10.0 mol dm3 hydrochloric acid, HCl (aq) commonly available laboratory reagents and equipment You may assume that any other material present in verdigris is unaffected by heating and is not acidic or basic. (i) Explain why a titration would not be a suitable method to determine the percentage of copper(II) carbonate in a sample of verdigris.[1] (ii) The 10.0 mol dm3 HCl (aq) is corrosive and too concentrated for use in the experiment. Describe how you would accurately prepare 250 cm3 of 0.500 mol dm3 hydrochloric acid from the 10.0 mol dm3 HCl (aq) provided. Include details of any apparatus, including their capacities in cm3, you would use.[2]UCLES 2017 9701/52/O/N/17<br /> PMT (iii) Identify a dependent variable that you could measure to determine the percentage of copper(II) carbonate in verdigris. Your answer should be based on a difference that you can identify between the reactions of copper(II) carbonate and copper(II) hydroxide with excess dilute hydrochloric acid.[1] (iv) Draw a diagram to show how you would set up apparatus and chemicals to measure the dependent variable identified in (iii). Label your diagram.UCLES 2017 9701/52/O/N/17 [2] [Turn over<br /> (v) Using the axes below, sketch a graph to show how the dependent variable you identified in (iii) would change during your experiment. Extend the graph beyond the point at which the reaction is complete. Label both axes. PMT (vi) A student carries out this experiment once. [2] Describe how this one experiment should be carried out to ensure that the results are as accurate as possible.[1]UCLES 2017 9701/52/O/N/17<br /> (vii) A student suspected that their 0.5 g sample of verdigris only contained CuCO3. Calculate the minimum volume, in cm3, of 0.500 mol dm3 HCl (aq) that would be needed for the complete reaction of the sample if the student was correct. [Mr: CuCO3 = 123.5] PMT volume of 0.500 mol dm3 HCl (aq) =cm3 [2] (b) The following information gives some of the hazards associated with the chemicals used in the procedure. Copper(II) carbonate hydroxide Hydrochloric acid The solid is classified as health hazard and is harmful if swallowed. Dispose of by reacting no more than 60 g in 1 dm3 of warm 1 mol dm3 ethanoic acid before pouring down a foul-water drain. Solutions equal to or more concentrated than 6.5 mol dm3 are classified as corrosive; solutions equal to or more concentrated than 2.7 mol dm3 but less concentrated than 6.5 mol dm3 are classified as moderate hazard and are irritant. Describe one relevant precaution, other than eye protection and a lab coat, that should be taken to keep the risk associated with the chemicals used to a minimum. Explain your answer.[1]UCLES 2017 9701/52/O/N/17 [Turn over<br /> PMT (c) Azurite is a blue copper-containing mineral. The copper compound in azurite has the formula Cu3(CO3)2(OH)2. This copper compound reacts with sulfuric acid according to the reaction shown. Cu3(CO3)2(OH)2(s) + 3H2SO4(aq) 3CuSO4(aq) + 2CO2(g) + 4H2O(l) A student performed a series of titrations on 1.50 g samples of solid azurite using 0.400 mol dm3 sulfuric acid. It can be assumed that any other material present in azurite does not react with sulfuric acid. The titration data is given in the table. experiment final reading / cm3 initial reading / cm3 titre / cm3 rough 25.50 0.00 25.50 24.05 0.15 23.90 32.70 8.30 24.40 The indicator for the titration was bromophenol blue. The student concluded that 24.15 cm3 of 0.400 mol dm3 sulfuric acid completely neutralised 1.50 g of azurite. (i) Using the students value of 24.15 cm3, calculate the percentage by mass of Cu3(CO3)2(OH)2 in the sample of azurite. Write your answer to three significant figures. [Mr: Cu3(CO3)2(OH)2 = 344.5] percentage by mass of Cu3(CO3)2(OH)2 in the sample of azurite =% [3]UCLES 2017 9701/52/O/N/17<br /> PMT (ii) Identify two possible problems with the students titration and suggest improvements to it. Problem 1Improvement 1Problem 2Improvement 2[3] [Total: 18]UCLES 2017 9701/52/O/N/17 [Turn over<br /> BLANK PAGE PMTUCLES 2017 9701/52/O/N/17<br />

Show answer