The equation for the thermal dehydration of hydrated copper(II) sulfate is:
CuSO4⋅5H2O(s)→CuSO4(s)+5H2O(g) \text{CuSO}_4\cdot 5\text{H}_2\text{O}(\text{s}) \rightarrow \text{CuSO}_4(\text{s}) + 5\text{H}_2\text{O}(\text{g}) CuSO4⋅5H2O(s)→CuSO4(s)+5H2O(g)A student investigates the dehydration of hydrated copper(II) sulfate using a crucible and lid heated on a clay pipe triangle.
She uses this method:
The table shows the student's results:
| Experiment | Mass before heating (g) | Mass after heating for 2 minutes (g) | Mass after heating for 4 minutes (g) | Mass after heating for 6 minutes (g) |
|---|---|---|---|---|
| 1 | 24.5 | 21.8 | 21.8 | 21.8 |
| 2 | 25.2 | 22.4 | 21.6 | 21.1 |
| 3 | 24.8 | 22.0 | 22.0 | 22.0 |
| 4 | 25.0 | 22.2 | 22.2 | 22.2 |
Why does the mass decrease during heating?
State the colours of the solids in the reaction:
(i) In which experiment might the dehydration not be complete? (ii) Give a reason for your choice. (iii) Which statement could explain why the dehydration might not be complete?
In another experiment, the student calculates that she should obtain a mass of 4.5 g of CuSO4(s)\text{CuSO}_4(\text{s})CuSO4(s) after completely dehydrating a sample of CuSO4⋅5H2O(s)\text{CuSO}_4\cdot 5\text{H}_2\text{O}(\text{s})CuSO4⋅5H2O(s). She actually obtains a mass of 4.1 g of CuSO4(s)\text{CuSO}_4(\text{s})CuSO4(s). Calculate the percentage yield in her experiment. Give your answer to two significant figures.
