Short free-response question
Water, strong bases and oxyacids
- Unit 8
- 4 points
- About 9 minutes
You can use a calculator on this question, just like on exam day.
A shorter multipart question that sticks to one or two topics. Each part usually asks for one calculation, claim or explanation. On the exam: 4 questions (Questions 4–7), part of the 1-hour-45-minute free-response section; calculator allowed.
The question and its sources
Answer the following questions about acid-base properties of aqueous solutions.
Table 1. Three oxyacids at 25 °C
| Acid | pKa |
|---|---|
| Hypochlorous acid, HOCl | 7.53 |
| Hypobromous acid, HOBr | 8.69 |
| Hypoiodous acid, HOI | 10.64 |
Source: Standard reference values, rounded
Suggested time: 9 minutes
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Part (a)
1 pointCalculate the pH of a 0.0025 M solution of Ba(OH)₂(aq) at 25 °C. Assume Ba(OH)₂ dissociates completely.
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Part (b)
1 pointAt 50 °C, the value of Kw is 5.5 × 10⁻¹⁴. Calculate the pH of pure water at 50 °C.
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Part (c)
1 pointA student claims that because its pH is less than 7, pure water at 50 °C is acidic. Do you agree or disagree with the student's claim? Justify your answer.
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Part (d)
1 pointUsing Table 1, explain why HOCl is a stronger acid than HOI in terms of molecular structure.
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