(a) If you were provided with anhydrous Na\(_2\)CO\(_3\), spatula and stirrer; (i) list three other materials you would require to prepare a standard soluti...

(a) Standard solution of Na₂CO₃

(i) Three other materials required: a chemical (weighing) balance, a volumetric (standard) flask, and a wash bottle of distilled water (a funnel and a beaker may also be used).

(ii) On adding dilute H₂SO₄ to the Na₂CO₃: brisk effervescence occurs and a colourless, odourless gas (CO₂) is evolved which turns lime water milky.

\[ Na_2CO_3 + H_2SO_4 \to Na_2SO_4 + H_2O + CO_2 \]

(b)(i) Distinguishing Zn²⁺ from Al³⁺

Add aqueous ammonia dropwise then in excess to each solution. Both give a white gelatinous precipitate; with Zn²⁺ the precipitate dissolves in excess ammonia (forming a colourless complex), whereas with Al³⁺ the precipitate is insoluble in excess ammonia. This distinguishes them.

(ii) Laboratory reagents:

• I. Produce NH₃ from (NH₄)₂SO₄: warm with sodium hydroxide (or calcium hydroxide).
• II. Differentiate AgCl from AgI: aqueous ammonia - AgCl dissolves, AgI does not.
• III. Dehydrate ethanol: concentrated sulphuric acid (or hot aluminium oxide).

(c) Reasons

(i) FeSO₄ solutions are freshly prepared because the Fe²⁺ ions are readily oxidised by air (oxygen) to Fe³⁺, so a fresh solution is needed to keep the iron as pure Fe²⁺.

(ii) The first jar of hydrogen is discarded because it is mixed with the air already in the apparatus, forming an explosive mixture; discarding it ensures the hydrogen collected afterwards is pure and safe.