An environmental chemist analyzes water samples drawn from three different lakes on…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
An environmental chemist analyzes water samples drawn from three different lakes on the same day. The lakes are at different temperatures, and the chemist records the following data:
• Sample 1: 10 °C, [H₃O⁺] = 1.4 × 10⁻⁷ M
• Sample 2: 25 °C, pOH = 7.08
• Sample 3: 60 °C, [OH⁻] = 1.1 × 10⁻⁷ M
Relevant values of the ionic product of water are provided:
10 °C: Kw=2.92×10−15
25 °C: Kw=1.00×10−14
60 °C: Kw=9.60×10−14
Answer all parts below.
(a) For each sample, calculate both pH and pOH to two decimal places.
(b) Determine the pH of neutral water at each of the three temperatures.
(c) Classify each lake as acidic, neutral, or basic relative to its own temperature, and justify each classification quantitatively.
(d) Rank the three samples from greatest acidity to greatest basicity using their hydronium-ion concentrations as the basis of comparison.
(e) Discuss how using pH 7.00 as a universal neutrality benchmark would misrepresent the relative acidity or basicity of the three samples, citing your results from parts (a) and (b).