Question

A solution of permanganate is standardized by titration with oxalic acid (). It required 54.77 mL of the permanganate solution to react completely with 0.3577 g of oxalic acid. The unbalanced equation for the reaction is What is the molarity of the permanganate solution

Answer 1

See explanation below

Step-by-step explanation:

The reaction between permanganate and oxalic acid, is a redox reaction, and this can be balance in acid medium or basic medium.

The reaction (without being balanced) is the following:

MnO₄⁻ + H₂C₂O₄ -------> Mn²⁺ + CO₂ + H₂O

Now, to get the molarity, we need to use the following expression:

M₁V₁ = M₂V₂ (1)

Where:

1: permanganate

2: oxalic acid

And the moles:

n = M*V (2)

However, expression (1) is only valid when the mole ratio between the two species, is the same (or 1:1). In this case, we do not know if the mole ratio is 1:1 because the reaction is unbalanced. Once the reaction is balanced we will see the mole ratio, and then, use the expression (1) to get the concentration.

Balancing the equation using the acid medium:

MnO₄⁻ + 8H⁺ + 5e⁻ -------> Mn²⁺ + 4H₂O Reduction

H₂C₂O₄ ------------> 2CO₂ + 2e⁻ + 2H⁺ Oxidation

Equalling both equations:

(MnO₄⁻ + 8H⁺ + 5e⁻ -------> Mn²⁺ + 4H₂O) *2

(H₂C₂O₄ ------------> 2CO₂ + 2e⁻ + 2H⁺) * 5

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2MnO₄⁻ + 16H⁺ + 10e⁻ -------> 2Mn²⁺ + 8H₂O

5H₂C₂O₄ ------------> 10CO₂ + 10e⁻ + 10H⁺

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2MnO₄⁻ + 5H₂C₂O₄ + 6H⁺ -------> 2Mn²⁺ + 10CO₂ + 8H₂O

This is the balanced equation. According to this, we can say that the mole ratio is 2:5, therefore expression (1) becomes:

2M₁V₁ = 5M₂V₂ ---> solving for M₁:

M₁ = 5M₂V₂ / 2V₁ (3)

Now that we know the expression, and the volume required, we need to get the concentration and volume of the acid. However, we do not know that, we only know the mass. So, we have to use the moles of oxalic acid to get the concentration. So replacing (2) in (3) we have:

M₁ = 5n₂ / 2V₁ (4)

Now, to get the moles, we need the molecular weight of the oxalic acid which is:

MM = (2*1) + (2*12) + (4*16) = 90 g/mol

The moles would be:

n = 0.3577 / 90 = 0.00397 moles

Finally, the concentration of the permanganate solution:

M₁ = 5*0.00397 / 2*0.05477

M₁ = 0.1812 M

Answer 2

0.1814 M

Step-by-step explanation:

From the balanced equation of reaction:

`2MnO_4^- + 16H^+ + 5C_2H_4^(2-) --> 2Mn^(2+) + 10CO_2 + 8H_2O`

2 mole of the permanganate requires 5 moles of oxalic acid.

Mole of 0.3577 g of oxalic acid =
`(mass)/(molar mass)`

= 0.3577/90.03

=0.00397 mole

Mole of permangante that will require 0.00397 mole of oxalic acid:

= 5 x 0.00397/2

= 0.00993 mole

Molarity of permanganate = mole/volume

Volume of permanganate = 54.77 mL = 0.05477 L

Molarity = 0.00993/0.05477

= 0.1814 M

The molarity of the permangante solution is 0.1814 M