#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?

Question

Mateo Aguilar · Accepted Answer

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.

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.

Ellie Andrews · Answer

undefined To determine if calcium hydroxide will precipitate, calculate the moles of Ca(NO3)2 and NaOH, then compare the number of moles of calcium ions (Ca^2+) with the number of moles of hydroxide ions (OH^-) available after the reaction. If the number of moles of Ca^2+ exceeds the number of moles of OH^-, calcium hydroxide will precipitate.