Question

What is the molar soulbility of calcium carbonate in pure water? the ksp value for calcium carbonate is 4.50x10-9. What is the molar solubility in 0.1 M CaCl.

Answer 1

Molar Solubility is given by S.When calcium carbonate is dissolved in water it dissociate into ions Ca²⁺ and CO₃^2-.

CaCO₃ --> Ca²⁺ + CO₃^2-

^{(S). (S)}

Now solubility product of CaCO₃ is gIven by

K_sp= [Ca²⁺][CO₃^2-]

= S*S

=S²

Given K_sp= 4.5 x 10^-9

S²= 4.5 x 10^-9

S= 6.7 x 10^-5

So molar solubility of Calcium carbonate in water is 6.7 x 10^-5

Now when CaCO3 is dissolved in CaCl₂.The solubility is effected due to presence of common ion Ca²⁺.

CaCl₂ --> Ca²⁺ + 2Cl^-

^{( 0.1). (0.1)}

CaCO3 --> Ca²⁺ + CO₃^2-

^{( S). (S)}

ThIs time solubility product is given by

K_Sp = [Ca²⁺] [CO₃^2-]

= [S + 0.1][S]

= S² + 0.1 S

K_sp= 0.1 S ( S² Can be neglected Value)

0.1 S= 4.5 x 10^-9

S= 4.5 x 10^-8

Thereforemolarsolubilityofcarbonate in 0.1 m  CaCl₂ is decreased to 4.5 x 10^-8