Question

What is the maximum concentration of a chromate ion, CrO₄^2-, that can be in solution before CaCrO₄ would predicate from a 0.050 M aqueous solution of Ca(NO₃)₂?

Answer 1

Ca(NO₃)₂.Calcium nitrate is composed of calcium ions, Ca²⁺, and nitrate ions, NO₃^–

=====================================

Because there are two NO₃^– ions for each Ca²⁺ ion in the compound,

each mole of Ca(NO₃)₂ that dissolves dissociates into

1 mol of Ca²⁺

and

2 mol of NO₃^–

^{===============================================}

CaCrO4 dissociates:
CaCrO4 ↔ Ca ²⁺ + CrO₄^2-

Ksp = [Ca2+] * [CrO4 2-]

but [Ca2+] = [CrO4 2-]

================================================

0.050 M aqueous solution of Ca(NO₃)₂

1 mol of Ca²⁺      =[ 0.050 M]

and

2 mol of NO₃^–     =[ 0.1 M]

=========================================

Ca2+] = [CrO4 2-] ==[ 0.050 ] M----------ANSWER