University:
Jackson College
Course:
CEM-141 | General Chemistry I
Academic year:

2024
Views:

395

Pages:

4
Author:

Jordyn Perkins

CHEM 12 Kw / pH / Neutrality Consider the following equilibrium: energy + 2 H₂O ⇌ H₃O⁺ + OH⁻ a) Explain how pure water can have a pH = 7.30. b) Calculate the value of Kw for the sample of water with a pH = 7.30. Consider the following equilibrium: 2 H₂O ⇌ H₃O⁺ + OH⁻ When water has a pH of 7.5, the temperature is: a) less than 25 °C and the solution is basic b) less than 25°C and the solution is neutral c) greater than 25 °C and the solution is basic d) greater than 25 °C and the solution is neutral. Write an equation representing the ionization of water and state both ion concentrations that exist for pure water to have a pH = 7.20. At 10°C, Kw = 2.95 x 10⁻¹⁵. a) Determine the pH of water at 10°C. b) State whether water at this temperature is acidic, basic, or neutral, and explain. At 20°C, the ionization constant of water is 6.76 x 10⁻¹⁵. Calculate the [H₃O⁺] of water at 20°C. Jan 2001 1. Consider the following equilibrium: energy + 2H₂O ⇌ H₃O⁺ + OH⁻ a) Explain how pure water can have a pH = 7.30. Solution: For Example: A lower temperature causes a shift to the left. The [H₃O⁺] drops as a result, and the pH increases. b) Calculate the value of Kw for the sample of water with a pH = 7.30. Solution: For Example: [H₃O⁺] = [OH⁻] = 1 x 10⁻⁷.₃⁰ ≈ 5.0 x 10⁻⁸ M Kw = [H₃O⁺][OH⁻] = (5.0 x 10⁻⁸)(5.0 x 10⁻⁸) = 2.5 x 10⁻¹⁵ April 1999 2. Consider the following equilibrium: 2H₂O ⇌ H₃O⁺ + OH⁻ When water has a pH of 7.5, the temperature is: A. less than 25°C and the solution is basic B. less than 25°C and the solution is neutral C. greater than 25°C and the solution is basic D. greater than 25°C and the solution is neutral Answer: B June 2003 3. Write an equation representing the ionization of water and state both ion concentrations that exist for pure water to have a pH = 7.20. (3 marks) Solution: For Example: H₂O(l) + H₂O(l) ⇌ H₃O⁺(aq) + OH⁻(aq) Since pH = 7.20, [H₃O⁺] = 6.3 x 10⁻⁸ M [H₃O⁺] = [OH⁻] = 6.3 x 10⁻⁸ M