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) → CuCl2(aq) + CO2(g) + H₂O(I) Cu(OH)2(s) + 2HCl(aq) → CuCl2(aq) + 2H2O(I)

1. (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. • 0.5g of verdigris • 10.0 mol dm⁻³ 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.
2. (a)(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]
3. (a)(ii)The 10.0moldm⁻³ HCl(aq) is corrosive and too concentrated for use in the experiment. Describe how you would accurately prepare 250cm³ of 0.500 moldm⁻³ hydrochloric acid from the 10.0 mol dm⁻³ HCl(aq) provided. Include details of any apparatus, including their capacities in cm³, you would use.[2]
4. (a)(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]
5. (a)(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.[2]
6. (a)(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. 0[2]
7. (a)(vi)A student carries out this experiment once. Describe how this one experiment should be carried out to ensure that the results are as accurate as possible.[1]
8. (a)(vii)A student suspected that their 0.5g sample of verdigris only contained CuCO3. Calculate the minimum volume, in cm³, of 0.500 moldm⁻³ HCl(aq) that would be needed for the complete reaction of the sample if the student was correct. [Mr: CuCO3 = 123.5] volume of 0.500 moldm⁻³ HCl(aq) = ...................................... cm³[2]
9. (b)The following information gives some of the hazards associated with the chemicals used in the procedure. Copper(II) carbonate hydroxide 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 dm⁻³ ethanoic acid before pouring down a foul-water drain. Hydrochloric acid Solutions equal to or more concentrated than 6.5 mol dm⁻³ are classified as corrosive; solutions equal to or more concentrated than 2.7 mol dm⁻³ but less concentrated than 6.5 mol dm⁻³ 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]
10. (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(I) A student performed a series of titrations on 1.50 g samples of solid azurite using 0.400 mol dm⁻³ 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 | rough | 1 | 2 ---|---|---|--- final reading/cm³ | 25.50 | 24.05 | 32.70 initial reading/cm³ | 0.00 | 0.15 | 8.30 titre/cm³ | 25.50 | 23.90 | 24.40 The indicator for the titration was bromophenol blue. The student concluded that 24.15cm³ of 0.400 moldm⁻³ sulfuric acid completely neutralised 1.50 g of azurite.
11. (c)(i)Using the student's 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]
12. (c)(ii)Identify two possible problems with the student's titration and suggest improvements to it. Problem 1 Improvement 1 Problem 2 Improvement 2[3]

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