Acid–alkali indicators

5 marks · Hard

For each pH value below, state whether the solution is strongly acidic, weakly acidic, neutral, weakly alkaline, or strongly alkaline.

(a)

pH = 2

[1 mark]

(b)

pH = 5

[1 mark]

(c)

pH = 7

[1 mark]

(d)

pH = 9

[1 mark]

(e)

pH = 12

[1 mark]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

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(a) strongly acidic

(b) weakly acidic

(d) weakly alkaline

(e) strongly alkaline

Common mistakes: Mixing up acid and alkali classifications; Not matching the provided pH ranges

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · 'strongly acidic' for pH = 2

B2 (b) · 1 mark · 'weakly acidic' for pH = 5

B3 (c) · 1 mark · 'neutral' for pH = 7

B4 (d) · 1 mark · 'weakly alkaline' for pH = 9

B5 (e) · 1 mark · 'strongly alkaline' for pH = 12

Worked solution

a) pH = 2 is in the range 0–3, so strongly acidic.

b) pH = 5 is in the range 4–6, so weakly acidic.

c) pH = 7 is neutral.

d) pH = 9 is in the range 8–10, so weakly alkaline.

e) pH = 12 is in the range 11–14, so strongly alkaline.