CAIE A-Level Chemistry 7.2.5 pH of Water, Acids and Alkalis

Practise classifying water, acidic solutions and alkaline solutions from their pH under standard conditions.

Exam points

identify pure water as pH 7 under standard conditions and do not generalise this value to every temperature
classify a solution below pH 7 as acidic and above pH 7 as alkaline under the stated conditions
use indicator or supplied reaction information to estimate a plausible pH range rather than only naming the class

[Maximum number: 2]

Solid magnesium nitride, $\mathrm{Mg}_{3} \mathrm{~N}_{2}$ , is a crystalline solid.

Explain why the solution produced in the reaction in (c)(ii) has a pH greater than 7. Refer to the products of the reaction in your answer.

M1 due to $\mathrm{OH}^{-}(\mathrm{aq})$

M2 EITHER acid-base reaction of water by ammonia OR dissociation of (some) $\mathrm{Mg}(\mathrm{OH})_{2}$

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