Answers

1. the molar solubility of Ca(OH)₂ is found using standard equilibirium techniques.

Ca(OH)₂(s) → ← Ca²⁺(aq) + 2 OH^–(aq)

K_sp = [Ca²⁺]_e[OH^–]_e² = 5.5×10^–6

Initial00

Change+x+2x

Initialx2x

5.5×10^–6 = (x)(2x)² = 4x³

x = 1.1×10^–2 or the molar solubility of calcium hydroxide is 0.011 M

2. The molar solubility in the buffer is found similarly, but using an initial condition for the hydroxide ion concentration and recalling that buffers prevent the change in pH, i.e., the hydroxide ion concentration is constant.

Ca(OH)₂(s) → ← Ca²⁺(aq) + 2 OH^–(aq)

K_sp = [Ca²⁺]_e[OH^–]_e² = 5.5×10^–6

Initial010^{–(14.00 – pH)}

Change+x+0

Initialx10^{–(14.00 – pH)}

5.5×10^–6 = (x)(10^{–(14.00 – pH)})²

x = 5.5×10^–6/(10^{–(14.00 – pH)})² = molar solubility of calcium hydroxide in the basic buffer.

Specific Answers:

ID	pH	[Ca(OH)2] (M) in buffer
100609933	13.33	1.2×10–4
100632970	13.70	2.2×10–5
100596753	13.53	4.8×10–5
100618542	13.42	7.9×10–5
100618538	13.38	9.6×10–5
100626787	13.87	1.0×10–5
100545177	13.77	1.6×10–5
100602992	13.92	7.9×10–6
100586074	13.74	1.8×10–5
100587691	13.91	8.3×10–6
100606074	13.74	1.8×10–5
100616957	13.57	4.0×10–5
100618957	13.57	4.0×10–5
100581063	13.63	3.0×10–5
100619666	13.66	2.6×10–5
100560742	13.42	7.9×10–5
100620751	13.51	5.3×10–5
100621664	13.64	2.9×10–5
100619615	13.15	2.8×10–4
100633109	13.09	3.6×10–4
100592774	13.74	1.8×10–5
100590750	13.50	5.5×10–5
100601613	13.13	3.0×10–4
100632056	13.56	4.2×10–5
100632536	13.36	1.0×10–4
100592879	13.79	1.4×10–5
100615379	13.79	1.4×10–5
100625701	13.01	5.3×10–4
100615701	13.01	5.3×10–4
100615959	13.59	3.6×10–5
100572083	13.83	1.2×10–5
100573485	13.85	1.1×10–5
100632625	13.25	1.7×10–4
100503074	13.74	1.8×10–5
100594495	13.95	6.9×10–6
100624250	13.50	5.5×10–5
100581427	13.27	1.6×10–4
100620954	13.54	4.6×10–5
100582162	13.62	3.2×10–5
100626946	13.46	6.6×10–5
100624349	13.49	5.8×10–5
100609595	13.95	6.9×10–6
100626067	13.67	2.5×10–5
100569640	13.40	8.7×10–5
100617520	13.20	2.2×10–4
100594578	13.78	1.5×10–5
100617955	13.55	4.4×10–5
100597793	13.93	7.6×10–6
100577231	13.31	1.3×10–4
100620513	13.13	3.0×10–4
100626984	13.84	1.1×10–5
100552296	13.96	6.6×10–6
100580103	13.03	4.8×10–4
100525178	13.78	1.5×10–5
100554018	13.18	2.4×10–4
100607833	13.33	1.2×10–4
100593933	13.33	1.2×10–4
100611711	13.11	3.3×10–4
100603680	13.80	1.4×10–5
100615282	13.82	1.3×10–5
100623614	13.14	2.9×10–4
100621990	13.90	8.7×10–6
100593947	13.47	6.3×10–5
100591331	13.31	1.3×10–4
100623320	13.20	2.2×10–4
100607225	13.25	1.7×10–4
100617595	13.95	6.9×10–6
100620188	13.88	9.6×10–6
100621865	13.65	2.8×10–5
100615506	13.06	4.2×10–4
100571481	13.81	1.3×10–5
100548460	13.60	3.5×10–5
100562052	13.52	5.0×10–5
100635001	13.01	5.3×10–4
100634602	13.02	5.0×10–4
100585818	13.18	2.4×10–4
100618119	13.19	2.3×10–4
100563490	13.90	8.7×10–6
100601642	13.42	7.9×10–5
100586432	13.32	1.3×10–4
100611460	13.60	3.5×10–5
100605394	13.94	7.3×10–6