A student was given a sample of colourless solution containing three cations and was asked to identify the cations. The student carried out a series of reactions as shown in the flow chart below.
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(i) From the information above, suggest three cations which could be in the sample and would form the precipitates A, B and C. Give the formula for each precipitate,<br>(ii) Give an additional test which would help to confirm the presence of each cation,<br>(iii) Name any other cations that would fit the requirements for precipitates A, B and C.

PLACEHOLDER ANSWER - the question has three written parts. (i) A is AgCl from $$\text{Ag}^+$$ (white and, unlike $$\text{PbCl}_2$$, insoluble in hot water), B is $$\text{BaSO}_4$$ from $$\text{Ba}^{2+}$$, and C is $$\text{Al(OH)}_3$$ from $$\text{Al}^{3+}$$. (ii) AgCl dissolves in ammonia solution; $$\text{Ba}^{2+}$$ gives an apple-green flame; $$\text{Al(OH)}_3$$ dissolves in excess NaOH but not in excess ammonia. (iii) $$\text{Hg}_2^{2+}$$ also fits A ($$\text{Hg}_2\text{Cl}_2$$, which turns black with ammonia); $$\text{Sr}^{2+}$$ (and to some extent $$\text{Ca}^{2+}$$) fits B; and $$\text{Zn}^{2+}$$ ($$\text{Zn(OH)}_2$$) or $$\text{Mg}^{2+}$$ ($$\text{Mg(OH)}_2$$) fits C.