# Given the following data, determine the % by mass of oxalate (C_2O_4^2-) in a sample of an iron...

## Question:

Given the following data, determine the % by mass of oxalate (C_2O_4^2-) in a sample of an iron oxalate complex with the general formula K_z[Fe_x(C_2O_4)_y].wH_2O.

The reaction between oxalate and permanganate is as follows:

6H^+ + 5(COOH)_2 + 2MnO_4^- ? 10CO_2 + 2Mn^2+ + 8H_2O

m(iron oxalate complex) used for titration = 0.100 g

C(KMnO_4) standard solution = 0.0200 M

Mw(C_2O_4^2-) = 88.02 g/mol

Titre volume = 11.82 mL

Enter your answers in the boxes provided to 3 significant figures. Do not enter units. Very large or small numbers can be entered in scientific notation - for example enter 1.23E-4 to represent 1.23 * 10^-4.

Step 1: Determine the number of moles of KMnO_4 (and thus MnO_4^-) in the titre: n(KMnO_4) = n(MnO_4^-) = C x V(L) = Answer ................ mol

Step 2: Determine the number of moles of C_2O_4^2- reacted with the KMnO_4: n(C_2O_4^2-) = n((COOH)_2) = n(MnO_4^-) x 5/2 = Answer ............. mol

Step 3: Determine the mass of C_2O_4^2- reacted, and thus the mass percentage of C2O42- in the sample: m(C_2O_4^2-) = n(C_2O_4^2-) x Mw(C_2O_4^2-) = Answer ............ g %m(C_2O_4^2-) = [m(C_2O_4^2-)/m(iron oxalate complex)] x 100 = Answer ............ %

## Redox Titration:

Redox titration is a form of quantitative chemical analysis with similar equipment and techniques involved to that of acid-base titration. The difference is that redox titration is based on electron transfer occurring between two elements in an overall redox reaction. This occurs between an element in a standard oxidizing/reducing titrant (burette) and an element in an unknown reducing/oxidizing analyte (flask). One way to monitor the reaction progress is by observing a color change in one of the reactants when it undergoes oxidation or reduction. A relatively permanent color change indicates the reaction endpoint. A very common choice for a standardized oxidizing titrant is potassium permanganate. The permanganate ion has a deep purple color, which changes to colorless when the manganese inside is reduced to the +2 state.

## Answer and Explanation: 1

The overall redox titration reaction equation in acidic solution is:

{eq}2MnO_4^- (aq) + 16H^+ (aq) + 5C_2O_4^{2-} (aq) \rightarrow 10CO_2 (g) + 2Mn^{2+} (aq) + 8H_2O (l) {/eq}

• Moles of permanganate ion used = {eq}V \times C = 0.01182 L \times 0.0200 M = 0.000236 mol {/eq}

For equivalence this requires:

• Moles of oxalate ion reactant = {eq}\dfrac{5}{2} \times 0.000236 mol = 0.000591 mol {/eq}
• Mass of oxalate ion reactant = {eq}0.000591 mol \times \dfrac{88.019g}{1mol} = 0.0520 g {/eq}
• Mass of iron oxalate complex in sample = {eq}0.100 g {/eq}
• Mass percent of oxalate in iron oxalate complex compound = {eq}\dfrac{0.0520 g}{0.100g} \times 100\% = 52.0 \% {/eq}