(a) An aqueous solution of salt Q was added to excess Sodium trioxocarbonate (V) solution in a test tube. There was effervescence, the test tube became warm...

(a) Inferences from adding salt Q to excess sodium carbonate (effervescence, the tube became warm, and a white precipitate formed):

1. Effervescence: a gas (carbon dioxide) is released from the carbonate, so the solution of Q is acidic, i.e. Q is an acid salt or a solution containing H\(^+\) ions (it liberates CO\(_2\) from the carbonate).
2. The tube became warm: the reaction is exothermic (it gives out heat), consistent with an acid neutralising the carbonate.
3. White precipitate: Q contains a metal cation whose carbonate is insoluble in water, e.g. Ca\(^{2+}\), Mg\(^{2+}\), Zn\(^{2+}\), Al\(^{3+}\) or Pb\(^{2+}\) (these form white insoluble carbonates).

(b) From the salts NH\(_4\)Cl, PbSO\(_4\), NaHCO\(_3\), Cu(NO\(_3\))\(_2\), ZnCO\(_3\):

• (i) Do not readily dissolve in water: PbSO\(_4\) and ZnCO\(_3\) (both insoluble).
• (ii) Produce effervescence with dilute mineral acids: NaHCO\(_3\) and ZnCO\(_3\) (carbonates/hydrogencarbonates give off CO\(_2\)).
• (iii) Decompose on heating: NaHCO\(_3\), Cu(NO\(_3\))\(_2\) and ZnCO\(_3\) (the hydrogencarbonate, nitrate and carbonate all decompose on heating).
• (iv) Dissolve in water to form an alkaline solution: NaHCO\(_3\) (sodium hydrogencarbonate gives a mildly alkaline solution).
• (v) Sublimes on heating: NH\(_4\)Cl (ammonium chloride sublimes).