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At 25°C, the dissociation constant of a base, BOH, is 1.0 × 10⁻¹². The concentration of hydroxyl ions in 0.01 M aqueous solution of the base would be:

1. 1.0 × 10⁻⁵ mol L⁻¹
2. 1.0 × 10⁻⁶ mol L⁻¹
3. 2.0 × 10⁻⁶ mol L⁻¹
4. 1.0 × 10⁻⁷ mol L⁻¹

Correct answer: 1.0 × 10⁻⁶ mol L⁻¹

Solution

The dissociation constant (Kb) is given as 1.0 × 10⁻¹², and the base concentration is 0.01 M. Using the formula for weak base dissociation, [OH⁻] = √(Kb × C), we calculate [OH⁻] = √(1.0 × 10⁻¹² × 0.01) = 1.0 × 10⁻⁶ mol L⁻¹.

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