Problem

Problem

Solid Ca(OH)2_2 is dissolved in water to make 150.0 mL of a saturated solution at 25 °C having [Ca2+]=0.0200 M[\text{Ca}^{2+}] = 0.0200\,\text{M}. A student pipets 10.0 mL of this saturated solution into a 100.0 mL volumetric flask and adds distilled water to the calibration line. (a) Calculate the initial [OH−][\text{OH}^-] in the saturated Ca(OH)2_2 solution (give the value before any dilution). (b) Determine the concentration of OH−\text{OH}^- in the volumetric flask after dilution. (c) Compute both the pOH and pH of the diluted solution, expressing each to the correct number of significant figures. (d) Briefly explain why a divalent metal hydroxide like Ca(OH)2_2 produces a different hydroxide ion concentration than an equimolar solution of a monovalent strong base such as NaOH.
Intuitive explanation

This problem is about dilution and the solubility product (KspK_{sp})—specifically, how ionic concentrations change when you dilute a saturated solution, and whether the solution remains saturated or becomes unsaturated. The key insight is that dilution reduces all ion concentrations proportionally, so you need to compare the new ion product to KspK_{sp} to determine if precipitation occurs or if the solution is now undersaturated.

Intuitive explanation

This problem is about dilution and the solubility product (KspK_{sp})—specifically, how ionic concentrations change when you dilute a saturated solution, and whether the solution remains saturated or becomes unsaturated. The key insight is that dilution reduces all ion concentrations proportionally, so you need to compare the new ion product to KspK_{sp} to determine if precipitation occurs or if the solution is now undersaturated.

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