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Sodium oxide (Na2O) reacts with water to give sodium hydroxide. When 20.0 g of sodium oxide is dissolved in 500 mL of water (assume the volume does not change), the concentration of the resulting NaOH solution is k x 10⁻¹ M. Find the nearest integer k. [Atomic masses: Na = 23.0, O = 16.0, H = 1.0]

1. 13
2. 6
3. 26
4. 10

Correct answer: 13

Solution

Convert mass of Na2O to moles, double it for NaOH moles, then divide by 0.5 L.

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