The equation for the thermal dehydration of hydrated cobalt(II) chloride is:
CoCl2⋅6H2O(s)→CoCl2(s)+6H2O(g) \text{CoCl}_2\cdot 6\text{H}_2\text{O}(\text{s}) \rightarrow \text{CoCl}_2(\text{s}) + 6\text{H}_2\text{O}(\text{g}) CoCl2⋅6H2O(s)→CoCl2(s)+6H2O(g)A student investigates the dehydration of hydrated cobalt(II) chloride 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 | 32.4 | 28.5 | 28.5 | 28.5 |
| 2 | 33.1 | 30.2 | 29.1 | 28.3 |
| 3 | 32.7 | 28.8 | 28.8 | 28.8 |
| 4 | 32.9 | 29.0 | 29.0 | 29.0 |
Why does the mass decrease during heating?
State the colours of the solids in the reaction:
In which experiment might the dehydration not be complete?
Give a reason for your choice.
Which statement could explain why the dehydration might not be complete?
In another experiment, the student calculates that she should obtain a mass of 5.2 g5.2\text{ g}5.2 g of CoCl2(s)\text{CoCl}_2(\text{s})CoCl2(s) after completely dehydrating a sample of CoCl2⋅6H2O(s)\text{CoCl}_2\cdot 6\text{H}_2\text{O}(\text{s})CoCl2⋅6H2O(s). She actually obtains a mass of 4.6 g4.6\text{ g}4.6 g of CoCl2(s)\text{CoCl}_2(\text{s})CoCl2(s). Calculate the percentage yield in her experiment. Give your answer to two significant figures.
