(a)(i) What is an acid? (ii) List three chemical properties of tetraoxosulphate (VI) acid (iii) Give two uses of tetraoxosulphate (VI) acid. (b)(i) Describe...

(a)(i) An acid is a substance that ionizes in water (or other suitable solvent) to produce hydrogen ions, \(H^+\), as the only positive ions. (More generally, a proton, \(H^+\), donor.)

(ii) Three chemical properties of tetraoxosulphate(VI) acid, \(H_2SO_4\):

• It reacts with bases and metallic oxides (neutralization) to form a salt (tetraoxosulphate(VI)) and water only, e.g. \(H_2SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O\).
• It reacts with reactive metals to liberate hydrogen gas, e.g. \(H_2SO_4 + Zn \rightarrow ZnSO_4 + H_2\).
• It reacts with trioxocarbonate(IV) salts to give carbon(IV) oxide, e.g. \(H_2SO_4 + Na_2CO_3 \rightarrow Na_2SO_4 + H_2O + CO_2\). (Hot concentrated \(H_2SO_4\) also acts as an oxidizing and a dehydrating agent.)

(iii) Two uses of \(H_2SO_4\): in the manufacture of fertilizers (e.g. ammonium tetraoxosulphate(VI)); as the electrolyte in lead-acid accumulators (car batteries). (Also used to make detergents and as a drying/dehydrating agent.)

(b)(i) Laboratory preparation of zinc tetraoxosulphate(VI) crystals from zinc oxide (insoluble base + acid method):

1. Warm some dilute tetraoxosulphate(VI) acid in a beaker.
2. Add zinc oxide (the insoluble base) a little at a time, stirring, until some remains undissolved (i.e. add the oxide in excess to ensure all the acid reacts).
3. Filter to remove the excess zinc oxide; the filtrate is zinc tetraoxosulphate(VI) solution.
4. Evaporate the filtrate to the point of crystallization (until a hot saturated solution is obtained).
5. Allow it to cool slowly so that crystals form; filter off the crystals and dry them between filter papers.

\[ZnO + H_2SO_4 \rightarrow ZnSO_4 + H_2O\]

(ii) Zinc oxide is amphoteric because it reacts with both acids and bases:

As a base (with acid): \[ZnO + H_2SO_4 \rightarrow ZnSO_4 + H_2O\]

As an acid (with alkali): \[ZnO + 2NaOH \rightarrow Na_2ZnO_2 + H_2O\]

(c)(i) The reaction \(Zn + CuSO_4 \rightarrow ZnSO_4 + Cu\) is a displacement (redox) reaction (zinc, being more reactive, displaces copper from its salt).

(ii) Mass of zinc that reacts with 8.0 g of \(CuSO_4\):

\[\text{moles of } CuSO_4 = \frac{8.0}{160} = 0.05\,mol\]

From the equation, 1 mole \(CuSO_4\) reacts with 1 mole \(Zn\), so moles of \(Zn = 0.05\,mol\).

\[\text{mass of } Zn = 0.05 \times 65 = 3.25\,g\]