Chemistry 5070 · O Level · Acid–base titrations

Acid–base titrations — practice question

A student carries out an experiment to work out the percentage by mass of potassium iodate(V), $\text{KIO}_3$, in a specimen of impure potassium iodate(V). The impure potassium iodate(V) sample is put into a container that has already been weighed, and the container is weighed again. mass of container + impure potassium iodate(V) = $8.20\,\text{g}$ mass of empty container = $5.28\,\text{g}$
(a)[1]

Calculate the mass of impure potassium iodate(V) used in the experiment.

(b)[1]

Why does the beaker need to be washed out, with the rinsings poured into the same container as the solution?

(c)[1]

Name the vessel used to prepare solution G.

(d)[1]

Which liquid should rinse the pipette immediately before it is used to measure $25.0\,\text{cm}^3$ of G?

(e)[1]

Why is it not necessary to measure exactly equal amounts of aqueous potassium iodide and dilute sulfuric acid in each titration?

(f)[4]

Use the diagrams to fill in the table and work out the average volume of L.

(g)[1]

Calculate the amount of substance of $\text{Na}_2\text{S}_2\text{O}_3$ in the average volume of L, $0.100\,\text{mol dm}^{-3}$ $\text{Na}_2\text{S}_2\text{O}_3$, used during the titration.

(h)[1]

Use the equation to find the amount of substance of $\text{I}_2$ in H in the conical flask. $2\text{Na}_2\text{S}_2\text{O}_3 + \text{I}_2 \rightarrow 2\text{NaI} + \text{Na}_2\text{S}_4\text{O}_6$

(i)[1]

Use the equation to find the amount of substance of $\text{KIO}_3$ that gives the amount of substance of $\text{I}_2$ calculated in (h). This is the amount of substance of $\text{KIO}_3$ in $25.0\,\text{cm}^3$ of G. $\text{KIO}_3 + 5\text{KI} + 3\text{H}_2\text{SO}_4 \rightarrow 3\text{I}_2 + 3\text{K}_2\text{SO}_4 + 3\text{H}_2\text{O}$

(j)[1]

Calculate the amount of substance of $\text{KIO}_3$ in $500.0\,\text{cm}^3$ of G.

(k)[1]

Calculate the $M_r$ of $\text{KIO}_3$. [$A_r$: K, 39; I, 127; O, 16]

(l)[1]

Use your answers to (j) and (k) to find the mass of potassium iodate(V), $\text{KIO}_3$, in the sample of impure potassium iodate(V).

(m)[1]

Use your answers to (a) and (l) to work out the percentage by mass of $\text{KIO}_3$ in the sample of impure potassium iodate(V).

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