Chemistry 5070 · O Level · Acid–base titrations

Acid–base titrations — practice question

Ammonium sulfate is a nitrogenous fertiliser. The nitrogen it contains helps plants to grow.
(a)[1]

How can the student tell that every last trace of ammonia has evolved?

(b)[1]

What colour is the solution in the conical flask before hydrochloric acid is added, and at the end-point?

(c)[4]

From the burette diagrams, fill in the table, tick the most reliable titrations, and work out the mean volume of hydrochloric acid used.

(d)[1]

Calculate the number of moles of hydrochloric acid in the average volume of $0.100\,\text{mol dm}^{-3}$ hydrochloric acid.

(e(i))[1]

Using the equation $\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$, deduce how many moles of sodium hydroxide are present in $25.0\,\text{cm}^3$ of $T$.

(e(ii))[1]

Calculate the number of moles of sodium hydroxide in $250\,\text{cm}^3$ of $T$.

(f)[1]

Calculate the number of moles of sodium hydroxide in $50\,\text{cm}^3$ of $2.00\,\text{mol dm}^{-3}$ sodium hydroxide.

(g)[1]

By subtracting your answer to (e)(ii) from your answer to (f), calculate the number of moles of sodium hydroxide that reacts with $25.0\,\text{cm}^3$ of $R$.

(h(i))[1]

Calculate the mass of ammonia formed from the original $25.0\,\text{cm}^3$ sample of $R$.

(h(ii))[1]

Calculate the mass of ammonia formed from $1\,\text{dm}^3$ of $R$.

(i)[2]

Using your answer to (h)(ii), calculate the concentration of ammonium sulfate in $R$. [$A_r$: N, $14$; H, $1$]

Worked solution & mark scheme

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