#2xx10^-3*L# of #NaOH# of #0.200*mol*L^-1# concentration is added to #1.00*L# of #1.00*mol*L^-1# #Ca(NO_3)_2(aq)#...will calcium hydroxide precipitate?

1 Answer
anor277
Mar 10, 2017

Calcium hydroxide has a solubility of #1.73*g*L^-1# under standard conditions. This should have been quoted in the question. Calcium hydroxide should not precipitate.

Explanation:

We work out the equivalent quantity of calcium hydroxide, for which we (i) need a stoichiometric equation:

#Ca^(2+) + 2HO^(-) rarr Ca(OH)_2(s) darr#

And (ii) equivalent quantities of the ions in solution:

#"Moles of sodium hydroxide,"# #=# #2.00xx10^-3Lxx0.200*mol*L^-1=4.0xx10^-4*mol#.

And thus when this is added to the bulk solution, we have #[HO^-]# #=# #(4.0xx10^-4*mol)/(1.002*L)=4.0xx10^-4*mol*L^-1#.

Given the stoichiometry, we thus have a solution that is NOMINALLY #2.0xx10^-4*mol*L^-1# with respect to calcium hydroxide.

And this is a mass solubility of,

#74.09*g*mol^-1xx2.0xx10^-4*mol*L^-1=14.8*mg*L^-1# or #"15 ppm"#.

And so calcium hydroxide should NOT precipitate.

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