Solved Examples on Solubility
Example 1: The Ksp of copper bromide, CuBr, is 8× 10–10. Calculate the molar solubility of copper bromide.
Solution:
CuBr (s) ⇢ Cu+(aq) + Br–(aq)
Ksp = Cu+ + Br–
Ksp = S × S
8× 10–10 = S2
S = √8 × 10–10
S = 2.8 × 10-5mol/L.
Cu+ = S = 2.8 × 10-5mol/L.
Br– = S = 2.8 × 10-5mol/L.
Example 2: The molar solubility of tin iodide SnI2 is 1.00 x 10-2 mol/L. Calculate the Ksp of this compound.
Solution:
The solubility equilibrium of SnI2 is,
SnI2(s) ⇢ Sn2+(aq) + 2I–(aq)
The Ksp expression is written as,
Ksp = [Sn2+][I–]2
1 mol of SnI2 Produces 1.0 mol of Sn2+, but 2.0 mol of I–.
[Sn2+] = 1.00 × 10-2M
[I–] = (2) × 1.00 × 10-2M
[I–] = 2.00 × 10-2M
Putting these values in Ksp expression
Ksp = (1.00 × 10-2)(2.00× 10-2)2
Ksp = 4 × 10-6 M2.
Example 3: Calculate the solubility of Silver chloride, Ksp of AgCl = 4 × 10-8?
Solution:
The chemical formula of calcium chloride is CaCl2. When dissolved in a polar solvent, calcium chloride molecules dissociate into calcium cations and two chloride anions. This equilibrium reaction can be expressed as:
AgCl ⇢ Ag++ Cl–
Therefore, the solubility product constant can be expressed as:
Ksp = [Ag+] [Cl–] .
Ksp = S× S
Ksp = S2
4 × 10-8 = S2
S = √4 × 10-8
S = 2 × 10-4 mol/L.
[Ag+] = [Cl–] = 2 × 10-4 mol/L.
Example 4: If solid CaCl2 equilibrates with pure water, what are [Ca2+] and [Cl–] the solution at equilibrium? [Ksp(PbCl2) = 2.1 × 10-5].
Solution:
CaCl2 ⇢ Ca2+ + 2Cl–
Ksp = [Ca2+] + [Cl–]2
Ksp = S × (2S)2
Ksp = 4S3
2.1 × 10-5 = 4S3
2.1 × 10-5 / 4 = S3
5.25 × 10-6 = S3
S = 1.73 × 10-2 mol/L
[Ca2+] = S = 1.73 × 10-2 mol/L
[Cl–] = 2S = 2 × 1.73 × 10-2
[Cl–] = 3.46 × 10-2 mol/L.
Solubility Formula
Solubility is defined as the maximum amount of solute that can be dissolved in a known amount of solvent at a particular temperature. A solution can be defined as a homogeneous mixture of one or more solutes in a solvent. Adding sugar cubes to a cup of tea or coffee is a very common example of a solution. And the property that helps sugar molecules dissolve is called solubility. Therefore, the term solubility can be defined as the property of a substance or solute that is soluble in a particular solvent. A solute is any component that can be liquefied in a solvent, either solid, liquid, or gas.
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