Other alkaline solutions

3 marks · Easy

Potassium carbonate ([32mK_2CO_3[0m) can make water alkaline without containing hydroxide ions in its formula.

(a)

Write the formula of the ion that makes a solution alkaline.

[1 mark]

(b)

Explain, using a chemical equation, how potassium carbonate forms an alkaline solution in water.

[2 marks]

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(a) OH^-

(b) K_2CO_3(aq) + H_2O(l) -> 2K^+(aq) + OH^-(aq) + HCO_3^-(aq) (Point for correct worded explanation if equation not given)

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Marking points

B1 (a) · 1 mark · States hydroxide ion (OH^-) as responsible for alkalinity.

M1 (b) · 1 mark · Gives chemical equation (accepts ionic) showing formation of OH^- ions from potassium carbonate and water.

M2 (b) · 1 mark · Explanation that hydroxide ions form, making the solution alkaline (accept in words if clear).

Worked solution

a) The ion is OH^- (hydroxide ion). b) Potassium carbonate reacts with water:

This reaction produces hydroxide ions (OH^-), which make the solution alkaline.