Chemistry 9701 · AS & A Level · Analytical techniques

Analytical techniques — practice question

A $0.17\,\text{g}$ portion of a Group 14 chloride, $\text{XCl}_4$, was treated with water, giving an oxide, $\text{XO}_2$, and $\text{HCl}$. Equation 1: $\text{XCl}_4(s) + 2\text{H}_2\text{O}(l) \rightarrow \text{XO}_2(s) + 4\text{HCl}(aq)$. The $\text{HCl}$ formed was collected in $100\,\text{cm}^3$ of $0.10\,\text{mol dm}^{-3}$ sodium hydroxide solution (present in excess). A titration then showed that the remaining sodium hydroxide solution needed $30.0\,\text{cm}^3$ of $0.20\,\text{mol dm}^{-3}$ hydrochloric acid for full neutralisation.
(a)[1]

Calculate the amount, in moles, of hydrochloric acid required to neutralise the unreacted sodium hydroxide solution during the titration.

(b)[1]

Write the equation for the reaction between hydrochloric acid and sodium hydroxide.

(c)[1]

Calculate the amount, in moles, of sodium hydroxide neutralised during the titration.

(d)[1]

Calculate the amount, in moles, of sodium hydroxide that reacted with the $\text{HCl}$ produced in equation 1.

(e)[1]

Calculate the amount, in moles, of $\text{HCl}$ formed in equation 1.

(f)[1]

Calculate the amount, in moles, of $\text{XCl}_4$ present in the original $0.17\,\text{g}$ sample.

(g)[1]

Calculate the molecular mass, $M_r$, of $\text{XCl}_4$.

(h)[2]

Calculate the relative atomic mass, $A_r$, of $X$ and suggest its identity.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: $6 \times 10^{-3}$ mol

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