What is Ksp of Ca(OH)2

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21.30 mL of 0.015M HCl is needed to titrate a 10.00mL saturated Ca(OH)2 solution at 25 degrees celsius. What is the Ksp of Ca(OH)2?

Mar 24th, 2015

The reaction equation is 2HCl (aq) + Ca(OH)2 (aq) => CaCl2 (aq) + 2H2O

The number of moles of HCl reacted: 0.015 mol/L * (21.30/1000) L = 3.195*10^{-4} mol

The number of moles of Ca(OH)2 reacted: 1.5975*10^{-4} mol (the ratio of the coefficients is 2:1).

The molar concentration of dissolved Ca(OH)2 was 1.5975*10^{-4} mol / (10.00/1000 L) = 0.01598 mol/L

When calcium hydroxide dissolves,   Ca(OH)2 => Ca2+ + 2 OH- and Ksp = [Ca2+] * [OH-]^2,

 where the concentrations are [Ca2+] = 0.01598; [OH-] = 2*0.01598 = 0.03196.

Finally, Ksp = 0.01598 * 0.03196^2 = 1.632 * 10^{-5}.  

Mar 24th, 2015

Where did the 1.5975*10^-4 come from for Ca(OH)2 come from? 

Mar 24th, 2015

From the balanced reaction equation the number of moles of Ca(OH)2 is half of the number of moles of HCl reacted, so 3.195*10^{-4} / 2 = 1.5975*10^{-4} mol. 

Mar 24th, 2015

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