Question detail
If the pKa of a weak acid is 4.75, what is the value of Ka?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
Question
Type
exam_style
Style
Topic
Acids and bases (A-level only)
Question
If the pKa of a weak acid is 4.75, what is the value of Ka?
Answer
The value of Ka is 1.78 x 10^-5.
Explanation
To find Ka from pKa, we use the formula Ka = 10^(-pKa). Substituting the given pKa, we calculate Ka = 10^(-4.75), which equals 1.78 x 10^-5. This question assesses the ability to convert between pKa and Ka.
Common mistake
Common Mistake in Ka and pKa Conversion
Students often confuse the relationship between Ka and pKa, incorrectly using the formula pKa = -log(Ka) without proper substitution.
To correctly convert between Ka and pKa, use the formula pKa = -log(Ka). For example, if Ka = 1.0 x 10^-5, substitute this value: pKa = -log(1.0 x 10^-5). Calculate: pKa = 5.0. Thus, the final answer is pKa = 5.0.
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