Sec 3 Combined Science (Chemistry) Qualitative Analysis topical questions

State the colour of the precipitate formed when aqueous sodium hydroxide is added to solutions containing: (a) Cu²⁺, (b) Fe²⁺, (c) Fe³⁺.

Name the reagent used to test for chloride ions, and state the positive result.

State the test and positive result for each gas: (a) oxygen, (b) ammonia.

A solution gives a white precipitate with a few drops of aqueous sodium hydroxide. State what happens when the sodium hydroxide is added in excess if the cation is (a) Ca²⁺, (b) Zn²⁺.

A colourless solid is thought to be a carbonate. (a) Describe a test to confirm the carbonate anion, giving the observation. (b) Write the ionic equation for the reaction that produces the gas.

Explain why dilute nitric acid, rather than dilute hydrochloric acid, is used to acidify a solution before the silver nitrate test for chloride ions.

Two colourless solutions contain Zn²⁺ and Al³⁺ respectively. Describe tests, and the results, that tell which is which using (a) aqueous ammonia and (b) aqueous sodium hydroxide.

A fertiliser is suspected to contain ammonium sulfate. (a) Describe the test that identifies the ammonium ion, giving the observation. (b) Describe the test that identifies the sulfate ion, giving the observation. (c) Write the ionic equation for the positive sulfate result.

A colourless solution X gives a white precipitate with a few drops of aqueous sodium hydroxide; the precipitate dissolves in excess. With aqueous ammonia, X gives a white precipitate that is insoluble in excess. (a) Identify the cation in X and explain your reasoning. (b) Which single observation would have to change for the answer to become Zn²⁺? (c) Write the ionic equation for the formation of the white precipitate with sodium hydroxide.

A blue solid is shaken with water: some dissolves to give a blue solution. The solution gives a light blue precipitate with NaOH(aq) insoluble in excess, and a light blue precipitate with aqueous ammonia that dissolves in excess to a deep blue solution. A fresh portion of the solution, acidified with dilute nitric acid, gives a white precipitate with barium chloride solution. (a) Identify the cation and the anion. (b) Name the salt. (c) Write the ionic equation for the precipitate formed with aqueous sodium hydroxide.

Three colourless solutions are labelled P, Q and R. Adding NaOH(aq) dropwise gives: P — no precipitate; Q — a white precipitate; R — a white precipitate. Warming P with the NaOH gives a gas that turns damp red litmus blue. Adding excess NaOH dissolves Q's precipitate but not R's. Adding aqueous ammonia to Q gives a white precipitate that dissolves in excess. Identify the cations in P, Q and R, quoting the evidence for each.

A student has an unknown colourless solution and performs the following tests. Test 1: dilute hydrochloric acid is added — no fizzing. Test 2: after acidifying with dilute nitric acid, silver nitrate solution is added — no precipitate. Test 3: after acidifying with dilute nitric acid, barium chloride solution is added — no precipitate. Test 4: the solution is warmed with NaOH(aq) and aluminium foil — a gas is released that turns damp red litmus blue. Identify the anion in the solution, explaining how each test contributed to the conclusion.