Solid is dissolved in water to make of a saturated solution at having

CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases

Problem

Solid

\mathrm{Ca(OH)_2}

is dissolved in water to make

150.0\text{ mL}

of a saturated solution at

25^\circ\text{C}

having

[\mathrm{Ca^{2+}}]=0.0200\text{ M}

. A student pipets

10.0\text{ mL}

of this saturated solution into a

100.0\text{ mL}

volumetric flask and adds distilled water to the calibration line. (a) Calculate the initial

[\mathrm{OH^-}]

in the saturated

\mathrm{Ca(OH)_2}

solution (give the value before any dilution). (b) Determine the concentration of

\mathrm{OH^-}

in the volumetric flask after dilution. (c) Compute both the

\mathrm{pOH}

and

\mathrm{pH}

of the diluted solution, expressing each to the correct number of significant figures. (d) Briefly explain why a divalent metal hydroxide such as

\mathrm{Ca(OH)_2}

produces a different hydroxide-ion concentration than an equimolar solution of a monovalent strong base such as

\mathrm{NaOH}