The amount of iron in steel can be determined by titration with dichromate. Firs

Question

The amount of iron in steel can be determined by titration with dichromate. First, the steel is dissolved in hydrochloric acid to oxidize all the iron to Fe^2+. An indicator is added that will react with excess dichromate. Then, potassium dichromate is added to the solution until the end point is reached. Cr_2 O^2-_7 + 6Fe^2+ + 14H^+ rightarrow 2Cr^3+ + 6Fe^3+ + 7H_2O For the analysis of 2.00 g of steel, the titration required 21.30 mL of 0.1800 M K_2Cr_2O_7. What was the mass percentage of iron in this steel sample?

Explanation / Answer

Moles of K2Cr2O7 required = molarity * volume in L = 0.1800 * 21.30 / 1000 = 0.00383 mol

From the balanced eqution,

1 mol of K2Cr2O7 is needed for 6 mol of iron

then, 0.00383 mol of K2Cr2O7 is needed for 6 * 0.00383 = 0.0230 mol of iron

So, Mass of iron = moles * molar mass = 0.0230 * 56 = 1.29 g.

% by mass of iron in the steel sample = (1.29 / 2.00) * 100 = 64.5 %

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