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Ksp of Calcium Hydroxide Report Sheet Be sure to show your work for any calculations Data: A50 Mass of CaCl2 used Volume of NaOH used Molarity of NaOH used Filtrate pH 167 Saturated solution pH

Answer 1

Using the pH of the Saturated solution, we can calculate [OH] in the solution:

pH of saturated solution is given as = 11.87

We know that:

pH + pOH = 14

Therefore:

11.87 + pOH = 14

pOH = 14-11.87

pOH = 2.13

pOH is used to calculate [OH] in the solution :

$pOH = -log[OH^{-}]$

$10^{-pOH} = [OH^{-}]$

$[OH^{-}] = 10^{-2.13}$

$[OH^{-}] = 0.0074$ or

$[OH^{-}] = 7.4\times 10^{-3} M$

	Ca	Ca2+ (aq)	+ 2 OH- (aq)
Initial		0	0
Change		x	2x
Equilibrium		0 + x = x	0 + 2x = 2x

As [OH^-] is 2x = 7.4 x 10^-3

x = 7.4 x 10^-3/2

x = 3.7 x 10^-3 , Therefore [Ca⁺²] = 3.7 x 10^-3

Ksp is given by:

Ksp =[Ca⁺²][OH^-]²

$Ksp= (3.7\times10^{-3}) \times (7.4\times10^{-3})^{2}$

$Ksp= 2.03\times 10^{-7}$

There are two ways to calculate Ksp:

One way is from the filtrate and the other way is calculating it from the Saturated solution.

You have only asked for Ksp using the saturated solution.

Ksp can be calculated from the filtrate by using the same method above but using the pH of the filtrate.

By comparing the Ksp values from both the methods and calculating the percent error, we can say which method is more accurate.

If the values differ, it is due to the different pH values which causes disruption in the solubility (Ksp), sometimes the volumes of the solution may not be accurate or there might be human error.