Question

1. (a) a white powder, m, dissolves in water to form a solution with a ph of 3.5. (i) state the effect of solution m on blue litmus paper. 1 (ii) when solution m is added to a solid, q, carbon dioxide gas is formed. describe, with a reason, the chemical composition of q. 2 (b) two unknown solutions containing magnesium and zinc ions were analysed. describe the chemical tests that can be done to show the presence of each ion. 3

Explanation:

Step1: Determine litmus - paper reaction

Solutions with pH < 7 are acidic. Blue litmus paper turns red in acidic solutions.

Step2: Identify solid Q

Acids react with carbonates to produce carbon - dioxide gas. So solid Q is a carbonate.

Step3: Test for magnesium and zinc ions

Add sodium hydroxide solution to the solutions. Magnesium ions form a white precipitate that is insoluble in excess sodium hydroxide. Zinc ions form a white precipitate that dissolves in excess sodium hydroxide to form a colorless solution.

Answer:

(a)(i) Blue litmus paper turns red.
(a)(ii) Q is a carbonate. Reason: Acids react with carbonates to produce carbon - dioxide gas.
(b) Test: Add sodium hydroxide solution to each solution. Observation for magnesium ions: A white precipitate forms and is insoluble in excess sodium hydroxide. Observation for zinc ions: A white precipitate forms initially and then dissolves in excess sodium hydroxide to form a colorless solution.