1.1

Question 1

Determination of the composition of copper (II) carbonate

Answer 1

Copper(II) carbonate basic, CuCO3•Cu(OH)2(s), is the dull green colour that forms on copper roofs. Copper oxidises in the air to form an approximately equimolar mixture of CuCO3 and Cu(OH)2.The percentage of CuCO3 in the mixture can be determined by reacting the mixture with an acid and calculating the amount of CO2 evolved

Question 2

aim

Answer 2

Aims
• To make accurate measurement of the mass of the sample, and of the volume of CO2 released in the reaction of the sample with an excess of H2SO4.
• To determine the percentage by mass of CuCO3 in a sample of CuCO3•Cu(OH)2(s).

Question 3

equipment

Answer 3

• balance accurate to two decimal places or more
• weighing boat or filter paper
• spatula
• conical flask (250 cm3)
• bung with delivery tube
• measuring cylinder (250 cm3)
• measuring cylinder (50 cm3)
• clamp stand with boss and clamp
• trough

Question 4

method

Answer 4

Record all relevant observations during the practical. You should record your results in an appropriate format.

1. Set up the apparatus as shown in the diagram below. (the water displacement one)
2. Weigh approximately 1.5 g of CuCO3·Cu(OH)2(s). Record the exact mass. Use the correct number of decimals and the correct unit.
3. Add the solid to the conical flask and replace the bung.
4. Using a 50 cm3 measuring cylinder, measure out 50 cm3 H2SO4(aq). (This is an excess.)
5. Remove the bung from the conical flask, quickly add the acid to the flask, and immediately replace the bung.
6. Collect the gas in the 250 cm3 measuring cylinder and record the final volume of carbon dioxide using an appropriate format.
7. If you have time, repeat the experiment.

Question 5

analyisis of results

Answer 5

Calculate the amount of carbon dioxide, CO2(g), collected in the measuring cylinder. Assume that 1 mol of gas occupies 24 000 cm3 at room temperature and pressure.
Copper(II) carbonate basic reacts with sulfuric acid as below:

CuCO3·Cu(OH)2(s) + 2H2SO4(aq)  2CuSO4(aq) + 3H2O(l) + CO2(g)

Deduce the amount of copper(II) carbonate, CuCO3(s), that reacted.
Calculate the percentage by mass of CuCO3 in the original sample of CuCO3·Cu(OH)2(s). Give your answer to an appropriate number of significant figures.

Question 6

1. Assuming your sample of CuCO3·Cu(OH)2(s) contains exactly equal amounts of CuCO3(s) and Cu(OH)2(s), what % by mass of CuCO3 would you expect?

Answer 6

1. Expected %(CuCO3) = = 55.9%

Question 7

2. Determine the size of the divisions on the measuring cylinder you used to collect the carbon dioxide. Calculate the percentage error in the value of the gas volume.

Answer 7

2. E.g. for a Class B measuring cylinder graduated to 2 cm3 but have half divisions to 1cm3.
   % error = = 0.71%

Question 8

3. Determine to how many decimal places the balance measures that you used to weigh the CuCO3·Cu(OH)2(s). Calculate the percentage error in the value of the mass.

Answer 8

3. E.g. for a balance accurate to 2 decimal places, and mass of CuCO3·Cu (OH)2(s) determined from two mass readings.
   % error = = 0.66%

Question 9

4. Explain why it is not necessary to calculate the percentage error in the volume of H2SO4(aq) used.

Answer 9

4. The acid is in excess, so the actual amount is not required for the calculation.

Question 10

5. Suggest two errors in the procedure that could lead to inaccuracies in your experimental value for the % by mass of CuCO3(s).

Answer 10

5. Some gas is lost as the bung is replaced.

Some CO2 dissolves in the water and is therefore not measured.

Question 11

6. For each error identified in (5.), state and explain what effect these errors would have on your final result.

Answer 11

6. The loss of gas means that less CO2 is collected. This gives a smaller % by mass CuCO3 than the actual value.

Question 12

7. Suggest two ways in which the experiment could be modified to give a more accurate value for the % by mass of CuCO3(s), giving reasons for your choices.

Answer 12

7. Put the solid in a small specimen tube in the conical flask, add the acid, replace the bung and then mix together.

Question 13

8. When copper rooftops turn green, the copper reacts with oxygen, water vapour and carbon dioxide in the air to form CuCO3·Cu(OH)2(s). Construct an equation for this reaction.

Answer 13

8. 2Cu(s) + H2O(g) + CO2(g) + O2(g) → CuCO3·Cu(OH)2 (s)

Question 14

9. Find out the names and locations of famous buildings which have copper roofs and explain why some architects use this material.

Answer 14

Examples include:
• NEMO – Museum of Science in Amsterdam;
• Vila Olimpica in Barcelona
• Vasa Museum, in Stockholm
• NB: The Statue of Liberty is also made of copper.
Copper is used because of its corrosion resistance, prestigious appearance, and ability to form complex shapes

Question 15

Hazard information Copper(II) carbonate basic, CuCO3·Cu(OH)2(s)

Answer 15

Harmful if swallowed

Causes skin, eye and respiratory irritation

Question 16

Hazard information H2SO4(aq)

Answer 16

Causes skin and eye irritation