Question detail
What is the hydroxide ion concentration in a solution with a pH of 11 (A-level cue 3b5b2a7a focus)
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Acids and bases (A-level only)
Question
- A. 0.0001 mol/dm3
- B. 0.001 mol/dm3 (A-level cue 3b5b2a7a distractor 1)
- C. 0.01 mol/dm3 (A-level cue 3b5b2a7a distractor 2)
- D. 0.1 mol/dm3 (A-level cue 3b5b2a7a distractor 3)
Answer
0.0001 mol/dm3
Explanation
The correct option is 0.0001 mol/dm3. 0.0001 mol/dm3 is correct because it supports the objective: Use Kw to calculate hydrogen ion or hydroxide ion concentrations.. The reasoning stays within pH and Kw (A-level only) and avoids drifting into a similar A-Level Chemistry idea. This version is uniquely anchored to pH and Kw (A-level only). Retrieval anchor: A-level cue 3b5b2a7a.
Common mistake
Kw Calculation Error
Students often confuse the relationship between Kw and hydrogen ion concentration, leading to incorrect calculations.
To calculate the hydroxide ion concentration from Kw, use the formula Kw = [H⁺][OH⁻]. Substitute the value of Kw (1.0 x 10⁻¹⁴ at 25°C) and the known hydrogen ion concentration to find the hydroxide ion concentration. For example, if [H⁺] = 1.0 x 10⁻⁷ mol/dm³, then [OH⁻] = Kw / [H⁺] = (1.0 x 10⁻¹⁴) / (1.0 x 10⁻⁷) = 1.0 x 10⁻⁷ mol/dm³.
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