Identification of metallic and non-metallic ions (revision - part 1)
Francine Taylor-Campbell, Contributor

Let us use our knowledge of the reactions of some cations and anions to answer some examination questions.

Q1. Identify each lettered substance below by giving its name and formula (with the aid of equations).

(a) Q is a sodium salt. When a solution of Q was added to aqueous silver nitrate, a white precipitate, R, was formed. This precipitate did not dissolve in dilute nitric acid.

(b) S is a sodium salt. When a solution of S was added to aqueous barium nitrate, a white precipitate, T, was formed. When dilute nitric acid was added to T, it dissolved and a gas, U, which turned lime water milky, was evolved.

(c) When aqueous sodium hydroxide was added to aqueous zinc chloride, a white precipitate, V, was formed. This precipitate dissolved in excess of sodium hydroxide to form a colourless solution in which zinc was present as a salt, W.

Q2. Describe what is observed (with the aid of equations) in each of the following reactions.

(a) Aqueous NaOH is added to aq iron(III) sulphate

(b) Dilute HCl is added to solid sodium carbonate

(a) Aqueous barium chloride is added to dilute sulphuric acid

(b) Aqueous silver nitrate is added to aq sodium chloride. (8 marks)

ANSWERS

Q1.

(a) The ion present is Cl- which means that R is AgCl(silver chloride) and Q is NaCl(sodium chloride). Ag+(aq) + Cl-(aq) = AgCl (white ppt).

(b) The gas produced, U, is CO2, which means that the ion is CO32-. T is BaCO3 (barium carbonate), hence the sodium salt S is Na2CO3 (sodium carbonate).

Ba2+(aq) + CO32- (aq) == BaCO3 (s) white

BaCO3(s) + HNO3 (aq) == Ba(NO3)2(aq) + H2O (l) + CO2(g)

(c) V is zinc hydroxide (Zn(OH)2) and in excess NaOH, W, which is sodium zincate (Na2ZnO2) is formed. Zn2+ (aq) + 2OH- (aq) == Zn(OH)2 (s)

Zn(OH)2(s) + 2NaOH (aq) == Na2ZnO2 (aq) + 2H2O (l)

ANSWERS

Q2.

(a) A rust-brown precipitate is formed which is insoluble in excess NaOH. Fe3+(aq) + 3OH-(aq) == Fe(OH)3 (s)

(b) Sodium carbonate would dissolve and a gas would be given off.

Na2CO3(s) + 2HCl (aq) == 2NaCl (aq) + H2O(l) + CO2 (g)

(c) A white precipitate will be seen which will remain insoluble.

Ba2+(aq) + SO42-(aq) == BaSO4(s)

(d) The silver nitrate would react with the chloride ions to form a white precipitate of silver chloride. Ag+(aq) + Cl-(aq) == AgCl (s)

Attempt the question given below using the guidelines shown. The answers will be discussed next week.

Q3. A student conducted a number of tests on an aqueous solution of Compound Y. The observations that were made are recorded in the table below. You are required to fill in the interferences that could be made based on the observations recorded.

vi. Which metal ion was present?

vii. Give a reason for your answer. (8 marks)

Francine Taylor-Campbell is an independent contributor. Send questions and comments to kerry-ann.hepburn@gleanerjm.com