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Question 25

An atmospheric chemist is investigating the acidity of microscopic droplets in a marine fog. They determine the following average parameters for a single droplet:

  • Mean volume of a droplet: 2.5×10−11 cm32.5 \times 10^{-11}\text{ cm}^32.5×10−11 cm3
  • Mean quantity of hydronium ions (H3O+\text{H}_3\text{O}^+H3​O+) per droplet: 1.5×10−18 mol1.5 \times 10^{-18}\text{ mol}1.5×10−18 mol
a.

Calculate the mean H3O+\text{H}_3\text{O}^+H3​O+ ion concentration within a marine fog droplet. Give your answer in mol dm−3\text{mol dm}^{-3}mol dm−3.

[2]
b.

The formula to calculate pH is:

pH=−log⁡10[H3O+] \text{pH} = -\log_{10} [\text{H}_3\text{O}^+] pH=−log10​[H3​O+]

where [H3O+][\text{H}_3\text{O}^+][H3​O+] is the hydronium ion concentration in mol dm−3\text{mol dm}^{-3}mol dm−3. Use your calculation from part (a) to find the mean pH of the droplets. Give your answer to 2 significant figures.

[2]
Markscheme

Analysis Questions

  1. A Level
  2. /Biology
  3. /Analysis

45 exam-style questions on OCR A A Level Biology Analysis. Each one has a worked solution and a mark scheme showing where the marks go.

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