Chapter Three · Chemical equilibrium · Chemistry. These are 10 questions from the Magmo3 bank on this lesson, from easy to hard. Solve each one, then open "Show answer and explanation". Magmo3 has 121 questions on this lesson, each with an explanation.
Which of the following acids ionises almost completely in aqueous solution and is therefore classified as a strong acid?
Correct answer: (D) Hydrochloric acid
Explanation: Hydrochloric acid ionises almost completely in water, making it a strong acid, whereas the others are weak acids.
All of the following statements about the solubility product (Ksp) are correct, EXCEPT:
Correct answer: (D) The concentration of the undissolved solid salt appears in its expression.
Explanation: The concentration of solid PbBr₂ remains almost constant, so it is left out and Ksp = [Pb²⁺][Br⁻]². The other three statements are the book's definition and expression.
When a solution of a weak acid is diluted by adding distilled water at constant temperature, which of the following happens to its degree of dissociation (α)?
Correct answer: (C) It increases
Explanation: Dilution shifts the ionisation equilibrium towards more ions, so the degree of dissociation increases.
A saturated solution of barium sulphate is kept in contact with excess solid barium sulphate. Which of the following additions increases the mass of the precipitate?
Correct answer: (D) Adding sodium sulphate solution
Explanation: Sodium sulphate supplies the common ion SO₄²⁻, which shifts the equilibrium backward and increases the mass of barium sulphate precipitate.
The self-ionisation of water is an endothermic process. When the temperature of pure water is raised above 25 °C, which of the following correctly describes what happens?
Correct answer: (B) Kw increases while the water remains neutral
Explanation: Heating drives the endothermic ionisation forward, increasing Kw, but [H⁺] still equals [OH⁻] so the water stays neutral.
A certain solution has a pH of 9 at 25 °C. Its pOH value and nature are:
Correct answer: (B) pOH = 5, basic
Explanation: pOH = 14 − 9 = 5, and since pH > 7 the solution is basic (alkaline).
What is the pH of a 0.001 M solution of hydrochloric acid (completely ionised) at 25 °C?
Correct answer: (B) 3
Explanation: [H⁺] = 1 × 10⁻³ mol/L, so pH = −log(10⁻³) = 3.
A saturated solution of calcium hydroxide has Ksp = 4 × 10⁻⁶ at 25 °C. What is the pH of the saturated solution? (log 2 = 0.3)
Correct answer: (D) 12.3
Explanation: s = 1 × 10⁻² mol/L, so [OH⁻] = 2s = 2 × 10⁻² mol/L, giving pOH = 1.7 and pH = 12.3.
A 0.1 M solution of phenol has an acid ionisation constant Ka = 1.0 × 10⁻¹⁰. Assuming the degree of dissociation is small, the hydrogen-ion concentration of the solution is:
Correct answer: (D) 3.16 × 10⁻⁶ mol/L
Explanation: [H+] = √(Ka·C) = √(1.0×10⁻¹⁰ × 0.1) = √(1.0×10⁻¹¹) = 3.16×10⁻⁶ mol/L.
Zinc hydroxide, Zn(OH)₂, has a solubility product Ksp = 4 × 10⁻¹⁸ (mol³/L³). What is its molar solubility in pure water?
Correct answer: (A) 1 × 10⁻⁶ mol/L
Explanation: Ksp = [Zn²⁺][OH⁻]² = (s)(2s)² = 4s³, so s³ = 10⁻¹⁸ and the molar solubility s = 1 × 10⁻⁶ mol/L.
The first 10 questions in every subject are free, each with an explanation.