Calculate the ionic strength and mean activity coefficient of 0.01 m k2so4 solution?
Answers
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Concept:
The ionic strength can be calculated by the formula calculating the sum of each ion’s molar concentration multiplied by the valence squared.
Ionic strength, I =(1/2) ∑ⁿ₁ (CₓZₓ²)
where C is the concentration and Z is the charge on each ion.
Given:
A solution of K₂SO₄ molarity of 0.01 M.
Find:
The ionic strength and the mean activity coefficient.
Solution:
(i) Ionic Strength, I
Ionic Strength of 0.01 M K₂SO₄,
I =(1/2) ∑ⁿ₁ (CₓZˣ²) = (1/2) [(0.01×1²) +(0.01×2²)]
I=(1/2) (0.01+0.04) = 0.05/2 = 0.025
Hence, the ionic strength of the solution of K₂SO₄ molarity of 0.01 M is 0.025.
(ii) The mean activity coefficient is a property that can be determined from measurements of such properties of solutions as the vapor pressure, solubility, freezing point, and electrical potential.
Mean activity coefficient, γ±
㏒ γ± = -A|(z+)(z-)| √(I)
where γ± is the mean ionic activity coefficient, A = 0.509 at 25°C for aqueous solution, (z+), (z-) are the charges on the ion and I is the ionic strength.
㏒ γ± = -0.509×|(+1)(-2)|×√(0.025) = -0.16096
Taking the power of 10 on both sides,
γ± = 0.6903
Hence, the Mean activity coefficient, γ± of 0.01 M K₂SO₄ is 0.6903.
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