Neco Model Questions Vol1 2025 Chemistry Question 40

Practice objective / multiple choice question 40 from the 2025 Neco Model Questions Vol1 Chemistry examination.

Neco Model Questions Vol1 2025 Chemistry Objective / Multiple Choice Medium Difficulty
Question 40 NECO_MODEL_QUESTIONS_VOL1 • 2025 • CHEMISTRY • objective

Calcium fluoride (CaF₂) has a solubility product \(K_{sp}=1.5\times10^{-10}\) at 25 °C. The solid is placed in a solution that already contains 0.20 M NaF.\n(a) Calculate the solubility of CaF₂ (in mol L⁻¹) and the concentration of Ca²⁺ ions at equilibrium.\n(b) Fluoride ion hydrolyses according to \(F^- + H_2O \rightleftharpoons HF + OH^-\) with \(K_b = \frac{K_w}{K_a}\) where \(K_a\) for HF is \(6.8\times10^{-4}\). Assuming the total fluoride concentration remains essentially 0.20 M, estimate the pH of the solution.

Answer Options

A. Solubility = 5.0×10⁻⁹ M; [Ca²⁺] = 5.0×10⁻⁹ M; pH ≈ 8.00
B. Solubility = 2.5×10⁻⁹ M; [Ca²⁺] = 2.5×10⁻⁹ M; pH ≈ 8.40
Correct Answer C. Solubility = 3.8×10⁻⁹ M; [Ca²⁺] = 3.8×10⁻⁹ M; pH ≈ 8.23
D. Solubility = 1.2×10⁻⁸ M; [Ca²⁺] = 1.2×10⁻⁸ M; pH ≈ 7.85
Correct Answer
C
Correct Option:
Solubility = 3.8×10⁻⁹ M; [Ca²⁺] = 3.8×10⁻⁹ M; pH ≈ 8.23

About This Question

This is Neco Model Questions Vol1 2025 Chemistry Question 40. It is one of the objective questions from the 2025 Neco Model Questions Vol1 Chemistry examination.

Difficulty level: Medium .

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