Chemistry 5070 · O Level · Acid–base titrations

Acid–base titrations — practice question

A student works out the percentage by mass of iron present in a sample of impure iron.
(a)[1]

Calculate the mass of impure iron used in the experiment if the beaker has a mass of $36.53\,\text{g}$ and the beaker plus impure iron has a mass of $38.31\,\text{g}$.

(b)[1]

Give a test and observation to identify hydrogen gas produced in the reaction $\text{Fe}(s) + 2\text{H}^+(aq) \rightarrow \text{Fe}^{2+}(aq) + \text{H}_2(g)$.

(c)[1]

Suggest how the student makes sure that no $\text{Fe}^{2+}(aq)$ is left on the filter paper.

(d)[2]

Suggest how the student should make sure that every drop of filtrate is transferred from the conical flask to the volumetric flask.

(e)[1]

Name the piece of apparatus used to transfer $25.0\,\text{cm}^3$ of solution P into the conical flask.

(f)[1]

Identify the solution used to wash out the burette before it is filled with solution Q.

(g)[4]

Use the diagrams to fill in the table and calculate the average volume of Q.

(h)[1]

Calculate the number of moles of potassium manganate(VII) in the average volume of $0.0100\,\text{mol dm}^{-3}$ solution Q.

(i)[1]

One mole of potassium manganate(VII) reacts with five moles of $\text{Fe}^{2+}(aq)$. Calculate the number of moles of $\text{Fe}^{2+}(aq)$ in $25.0\,\text{cm}^3$ of P.

(j)[1]

Calculate the number of moles of $\text{Fe}^{2+}(aq)$ in $500\,\text{cm}^3$ of P.

(k)[1]

Calculate the mass of iron in $500\,\text{cm}^3$ of P. [$A_r(\text{Fe}) = 56$]

(l)[1]

Use your answers to (a) and (k) to calculate the percentage by mass of iron in the impure iron.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: 1.78 g of impure iron

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