A scientist heated 6.50 g6.50\text{ g}6.50 g of hydrated cobalt(II) chloride in an open crucible to drive off its water of crystallisation.
The reaction is:
hydrated cobalt(II) chloride (solid)→anhydrous cobalt(II) chloride (solid)+water vapour (gas) \text{hydrated cobalt(II) chloride (solid)} \rightarrow \text{anhydrous cobalt(II) chloride (solid)} + \text{water vapour (gas)} hydrated cobalt(II) chloride (solid)→anhydrous cobalt(II) chloride (solid)+water vapour (gas)The scientist weighed the contents of the crucible after every 3 minutes of heating. The results are shown in the table below:
| Total heating time (minutes) | Mass of contents of crucible (grams) |
|---|---|
| 0 | 6.50 |
| 3 | 5.82 |
| 6 | 5.20 |
| 9 | 4.75 |
| 12 | 4.42 |
| 15 | 4.21 |
| 18 | 4.15 |
| 21 | 4.15 |
Find the minimum heating time needed for all of the water of crystallisation to be completely removed.
Calculate the total mass of water vapour released during the heating process.
53 exam-style questions on AQA GCSE Chemistry 3.1 Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations, covering 3.1.1 Conservation of mass and balanced chemical equations, 3.1.2 Relative formula mass, 3.1.3 Mass changes when a reactant or product is a gas, and 3.1.4 Chemical measurements. Each one has a worked solution and a mark scheme showing where the marks go.