Question

What is the equilibrium Co²⁺ concentration when 1.64 L of a 0.200 M cobalt(II) sulfate solution are mixed with 1.72 L of a 0.357 M potassium carbonate solution?

[Co²⁺] =____M

Answer 1

Chemical equation between K₂CO₃ and CoSO₄ will be as follows.

CoSO₄ + K₂CO₃ --> CoCO₃ + K₂SO₄

Co²⁺ + CO₃^2- --> CoCO₃

First of all we have to find the number of moles of Co²⁺ and CO₃^2- available for reaction.

for that we use the equation, Weight = MM'V/1000 where M is the molarity, M' is the molecular mass and V is the volume in ml.

We know Number of moles=(Weight)/(Molecular Mass)

So Number of moles of Co²⁺ = 0.200*1.64 = 0.328 mole (M=0.200, V=1.64, Molecular mass is canceled)

Number of moles of CO₃^2- = 0.357*1.72 = 0.61404 mole

Then,

(In above picture we can see that,there require 0.328 Co²⁺ to react with 0.328 CO₃^2- to obtain 0.328 CoCO₃ )

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Thus we can find the equilibrium concentration of Co²⁺ in the above reaction if we are provided with the fromation consatnt(K_f ) value.

[Co²⁺] = [CoCO₃]/(K_f*[CO₃^2-])

[Co2+] =(0.328)/(0.28604*K_f)

(x in RHS is neglected for convenience)