Practice question

MCQ

Question

A solution contains 30 ppm of Na₂SO₄ by mass in water. What is its molarity if the density is 1 g/mL? (Molar mass: Na₂SO₄ = 142 g/mol)

Options

Choose one · Correct answer highlighted

2.0 × 10⁻⁴ M 2.5 × 10⁻⁴ M 2.113 × 10⁻⁴ M Correct 1.5 × 10⁻⁴ M

Explanation

30 ppm = 30 g Na₂SO₄ in 10⁶ g solution. Volume = 10⁶/1 = 10⁶ mL = 1000 L. Moles = 30/142 ≈ 0.2113 mol; molarity = 0.2113/1000 ≈ 2.113 × 10⁻⁴ M.

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