Question

`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?

Answer 1

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.