Chemistry 9701 · AS & A Level · Analytical techniques
Analytical techniques — practice question
Acidified potassium dichromate(VI) is able to oxidise ethanedioic acid, $\text{H}_2\text{C}_2\text{O}_4$. The two relevant half-equations are given below:
$\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6e^- \rightarrow 2\text{Cr}^{3+} + 7\text{H}_2\text{O}$
$\text{H}_2\text{C}_2\text{O}_4 \rightarrow 2\text{CO}_2 + 2\text{H}^+ + 2e^-$
(a)[2]
State the complete equation for the reaction of acidified dichromate(VI) ions with ethanedioic acid.
(b(i))[1]
Calculate the amount, in moles, of dichromate(VI) ions that reacted with the ethanedioic acid sample.
(b(ii))[1]
Calculate the amount, in moles, of ethanedioic acid in the sample.
(b(iii))[1]
Calculate the relative molecular mass, $M_r$, of the hydrated ethanedioic acid.
(b(iv))[1]
Calculate the value of $x$ in $\text{H}_2\text{C}_2\text{O}_4 \cdot x\text{H}_2\text{O}$.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Correctly balanced equation $Cr_2O_7^{2-} + 8H^+ + 3H_2C_2O_4 \rightarrow 2Cr^{3+} + 6CO_2 + 7H_2O$” …