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What is the H⁺ ion concentration of a solution prepared by dissolving 4 g of NaOH (Atomic weight of Na = 23 amu) in 1000 mL water?

1. 10⁻¹⁰ M
2. 10⁻⁴ M
3. 10⁻¹ M
4. 10⁻¹³ M

Correct answer: 10⁻¹³ M

Solution

NaOH is a strong base and dissociates completely in water. The molar mass of NaOH is 40 g/mol, so 4 g corresponds to 0.1 mol. In 1 L of water, the OH⁻ concentration is 0.1 M. Using pOH = -log[OH⁻], pOH = 1, and pH = 14 - pOH = 13. Thus, [H⁺] = 10⁻¹³ M.

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