NaOH is added to sea water containing 0.050 moles per liter of Mg²⁺ ion until the pH reaches 12.0. A certain quantity of Mg(OH)₂ precipitates. How many parts per billion of magnesium are left behind in the solution? The K_sp of Mg(OH)₂ is 7.1 × 10^-¹².Hint: Find [Mg²⁺^{], then convert to ppb.}

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Quizplus · Accepted Answer

At pH 12, [OH⁻] = 10⁻² M. Using Ksp = [Mg²⁺][OH⁻]², we find [Mg²⁺] = 7.1 × 10⁻⁸ M. Converting to ppb: (7.1 × 10⁻⁸ mol/L) × (24.305 g/mol) × (10⁹ µg/g) = 1.7 ppb.

NaOH Is Added to Sea Water Containing 0