Acid–alkali indicators
2 marks · EasyExplain why a solution with pH 11 is classified as strongly alkaline rather than weakly alkaline.
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A solution with pH 11 is classified as strongly alkaline because, according to the pH classification, strongly alkaline solutions have pH values from 11 to 14. Weakly alkaline solutions have pH values of 8 to 10.
Also accept: pH 11 falls in the strongly alkaline range
Common mistakes: Saying pH 11 is only weakly alkaline
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Marking points
M1 · 1 mark · Identifies the correct pH range for strongly alkaline solutions (11–14).
A1 · 1 mark · States that pH 11 fits in this range (or pH 8–10 is weakly alkaline).
Worked solution
Strongly alkaline solutions have pH values between 11 and 14. A pH of 11 is in this range, so it is classified as strongly alkaline. Weakly alkaline solutions only cover pH 8–10.