Question

A 25.0 mL solution of 0.0430M EDTA was added to a 51.0mL sample containing an unknown concentration of V3+. All V3+ present formed a complex, leaving excess EDTA in the solution. This solution was back-titrated with a 0.0360 M Ga3+ solution until all the EDTA reacted, requiring 15.0mL of the Ga3+ solution. What was the original concentration of the V3+ solution?

[V3+]=

Please show work on this problem. I really want to learn how to do these problems, not just get the answers! Thank you so much in advance as I know it takes a while. I really appreciate it :)

Answer 1

Let the volume of excess EDTA be V₂ mL.

For the second part,

Molarity of Ga³⁺ solution, M₁ = 0.0360 M

Volume of Ga³⁺ solution required for titration, V₁ = 15.0 mL

Molarity of EDTA solution, M₂ = 0.0430 M

M₁V₁ = M₂V₂

0.0360 15.0 = 0.0430 V₂

V₂ = 12.6 mL

So the amount of EDTA actually reacted with V³⁺ = 25.0 - 12.6 = 12.4 mL

Now, considering first part

Molarity of V³⁺ solution = M₁ = Our aim to find out

Volume of V³⁺ solution required for formation of complex, V₁ = 51.0 mL

Molarity of EDTA solution, M₂ = 0.0430 M

Molarity of EDTA solution required for formation of complex, V₂ = 12.4 mL

M₁V₁ = M₂V₂

M₁ 51.0 = 0.0430 12.4

M₁ = 0.01 M

Therefore, original concentration of V³⁺ solution is 0.01 M.