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The concentration of oxalate ion (C2O42-) in a sample can be determined by titration with a solution of permanganate ion (MnO4-) of known concentration. The net ionic equation for this reaction is 2MnO4- + 5C2O42- + 16H+ --> 2Mn2+ + 8H2O + 10CO2 A 30.00 mL sample of an oxalate solution is found to react completely with 21.93 mL of a 0.1725 M solution of MnO4-. What is the oxalate ion concentration in the sample?

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Answer:

0.3152 M

Explanation:

The reaction that takes place is:

  • 2MnO₄⁻ + 5C₂O₄⁻² + 16H⁺ → 2Mn⁺² + 8H₂O + 10CO₂

First we calculate the MnO₄⁻ moles used up in the titration, by multiplying the volume times the concentration:

  • 21.93 mL * 0.1725 M = 3.783 mmol MnO₄⁻

Then we convert MnO₄⁻ moles to C₂O₄⁻² moles:

  • 3.783 mmoles MnO₄⁻ * [tex]\frac{5mmolC_2O_4}{2mmolMnO_4}[/tex]= 9.457 mmol C₂O₄⁻²

Finally we calculate the oxalate ion concentration, by dividing the moles by the volume:

  • 9.457 mmol C₂O₄⁻² / 30.00 mL = 0.3152 M

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