An analytical chemist is determining the formula of a batch of hydrated zinc sulfate, ZnSO4⋅xH2O\text{ZnSO}_4 \cdot x\text{H}_2\text{O}ZnSO4⋅xH2O, to verify its purity for agricultural use.
A crucible is first weighed empty, then filled with a sample of the hydrated crystals and weighed again. After heating the crucible strongly with a Bunsen burner to drive off all the water of crystallisation, it is allowed to cool and is reweighed. This cycle of heating, cooling, and weighing is repeated until a constant mass is reached.
The chemist's results are shown below:
Use these results to calculate the value of xxx in the formula of ZnSO4⋅xH2O\text{ZnSO}_4 \cdot x\text{H}_2\text{O}ZnSO4⋅xH2O.
[MrM_{\text{r}}Mr values: ZnSO4=161\text{ZnSO}_4 = 161ZnSO4=161, H2O=18\text{H}_2\text{O} = 18H2O=18]
80 exam-style questions on Edexcel IGCSE Chemistry Chemical formulae, equations and calculations. Each one has a worked solution and a mark scheme showing where the marks go.