Zinc carbonate occurs in a basic form, which means that zinc hydroxide is also present. The chemical formula of basic zinc carbonate can be written as ZnCO₃.yZn(OH)₂, where y may not be an integer. In this experiment you will heat basic zinc carbonate to decompose it and use your results to determine the value of y. When basic zinc carbonate is heated, it decomposes as shown. ZnCO₃.yZn(OH)₂(s) → (1 + y)ZnO(s) + CO₂(g) + yH₂O(g) FA 5 is basic zinc carbonate, ZnCO₃.yZn(OH)₂.

1. (a)(i)State the observation(s) you made while you were heating FA 5.
2. (a)(ii)State the observation(s) you made once the residue had cooled down.
3. (a)(results)Prepare a table for all your results from Experiments 1 and 2 in the space on page 5. Experiment 1: Weigh a crucible with its lid and record the mass. Add 2.1-2.5g of FA 5 to the crucible. Weigh the crucible and lid with FA 5 and record the mass. Place the crucible in the pipe-clay triangle on top of the tripod. Heat the crucible and contents gently for 1 minute with the lid on. Remove the lid. Heat the crucible and contents strongly, with the lid off, for approximately 4 minutes. Replace the lid and leave the crucible and residue to cool for at least 5 minutes, before re-weighing it with the lid on. Record the mass. Calculate, and record in your table, the mass of FA 5 used and the mass of residue obtained. Experiment 2: Repeat the procedure used in Experiment 1, using 1.5-1.9g of FA 5 and using the other crucible and lid. Record the three balance readings made during the experiment. Calculate and record the mass of FA 5 used and the mass of residue obtained.[6]
4. (b)(i)Calculate the relative formula mass, Mᵣ, of zinc hydroxide, Zn(OH)₂. Mᵣ of Zn(OH)₂ = ..............................................[1]
5. (b)(ii)Using your answer to (i), write down an expression, in terms of y, for the relative formula mass, Mᵣ, of basic zinc carbonate, ZnCO₃.yZn(OH)₂. Mᵣ of ZnCO₃.yZn(OH)₂ = ..............................................[1]
6. (b)(iii)Using the mass of ZnCO₃.yZn(OH)₂ from Experiment 1 and your answer to (ii), write down an expression, in terms of y, for the number of moles of ZnCO₃.yZn(OH)₂ that you heated in Experiment 1. moles of ZnCO₃.yZn(OH)₂ = .............................................. mol[1]
7. (b)(iv)Using your answer to (iii) and the equation below, write an expression, in terms of y, for the number of moles of zinc oxide produced in Experiment 1. ZnCO₃.yZn(OH)₂(s) → (1 + y)ZnO(s) + CO₂(g) + yH₂O(g) moles of ZnO produced = .............................................. mol[1]
8. (b)(v)Use your results from Experiment 1 to calculate the number of moles of zinc oxide, ZnO, obtained in the residue. You may assume complete decomposition has occurred. moles of ZnO = .............................................. mol[1]
9. (b)(vi)Using your answers to (iv) and (v), calculate the value of y to one decimal place. y = ..............................................[1]
10. (c)(i)Apart from altering the balance or the masses of FA 5 used, state one improvement you could make to the experimental procedure to improve its accuracy.[1]
11. (c)(ii)Which experiment should be more accurate, Experiment 1 or Experiment 2? Explain your answer.[1]