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: Recall litmus - paper property

Acids turn blue litmus paper red. Since solution M has a pH of 3.5 (acidic), it will turn blue litmus paper red.

Step2: Identify solid Q

Acids react with carbonates to produce carbon - dioxide gas. So, solid Q is a carbonate because when an acid (solution M) reacts with it, carbon dioxide is formed.

Step3: Test for magnesium and zinc ions

For magnesium ions: Add sodium hydroxide solution. A white precipitate that is insoluble in excess sodium hydroxide solution indicates magnesium ions.
For zinc ions: Add sodium hydroxide solution. A white precipitate is formed initially. The precipitate dissolves in excess sodium hydroxide solution to form a color - less solution, indicating zinc ions.

Answer:

(a)(i) The blue litmus paper will turn red.
(a)(ii) Solid Q is a carbonate. Reason: Acids react with carbonates to produce carbon dioxide gas, and solution M (an acid) reacts with Q to produce carbon dioxide.
(b) For magnesium ions: Add sodium hydroxide solution. Observation: A white precipitate is formed which is insoluble in excess sodium hydroxide solution. For zinc ions: Add sodium hydroxide solution. Observation: A white precipitate is formed initially, and it dissolves in excess sodium hydroxide solution to form a color - less solution.