One salt used as a dietary supplement is hydrated zinc sulfate, $\text{ZnSO}_4\cdot x\text{H}_2\text{O}$, which is a colourless crystalline solid.\n\nZinc sulfate crystals can be made in a school or college laboratory by reacting dilute sulfuric acid with a suitable zinc compound.\n\nGive the formulae of two simple zinc compounds that could each react with dilute sulfuric acid to form zinc sulfate.
A straightforward way to find the value of $x$ in $\text{ZnSO}_4\cdot x\text{H}_2\text{O}$ is to heat it carefully so that the water is removed.\n\n$\text{ZnSO}_4\cdot x\text{H}_2\text{O}(s) \rightarrow \text{ZnSO}_4(s) + x\text{H}_2\text{O}(g)$\n\nA student put a sample of the hydrated zinc sulfate into a weighed boiling tube and weighed it again. He then heated the tube briefly, cooled it and weighed it while cold. This was done four more times. The final readings are shown below.\n\nWhy was the boiling tube heated, cooled and reweighed four times?
Why was the boiling tube heated, cooled and reweighed four times?
Calculate the amount, in moles, of the anhydrous salt formed.
Calculate the amount, in moles, of water driven off by heating.
Use your results from (ii) and (iii) to calculate the value of $x$ in $\text{ZnSO}_4\cdot x\text{H}_2\text{O}$.
For many people, taking about $15\,\text{mg}$ per day of zinc will be enough to prevent deficiencies.\n\nZinc ethanoate crystals, $(\text{CH}_3\text{CO}_2)_2\text{Zn}\cdot 2\text{H}_2\text{O}$, may be used for this purpose.\n\n(i) What mass of pure crystalline zinc ethanoate ($M_r = 219.4$) must be taken to provide a dose of $15\,\text{mg}$ of zinc?\n\n(ii) If this dose is taken in solution as $5\,\text{cm}^3$ of aqueous zinc ethanoate, what is the concentration of the solution used? Give your answer in $\text{mol dm}^{-3}$.