Home / AS & A Level Chemistry 7.2 Brønsted–Lowry theory of acids and bases Exam Style Practice Questions Paper 1
Four reaction mixtures are listed.
1 \(\mathrm{(NH_4)_2SO_4(aq)}\) and \(\mathrm{NaOH}\)
2 \(\mathrm{NH_4Cl(aq)}\) and \(\mathrm{Ba(OH)_2}\)
3 \(\mathrm{NH_4Cl(aq)}\) and \(\mathrm{Na_2O}\)
4 \(\mathrm{(NH_4)_3PO_4(aq)}\) and \(\mathrm{HCl}\)
Which reaction mixtures produce ammonia as a product?
Correct Answer: \( \boxed{\mathrm{A}} \)
Ammonium ions react with alkalis to produce ammonia:
\(\mathrm{NH_4^+ + OH^- \rightarrow NH_3 + H_2O}\)
Mixtures 1 and 2 contain soluble alkalis, while in mixture 3, \(\mathrm{Na_2O}\) reacts with water to form \(\mathrm{NaOH}\), which also releases ammonia.
Mixture 4 contains hydrochloric acid, which converts ammonia into ammonium ions rather than producing ammonia.
Therefore, the correct answer is (A).
R is the aqueous solution of an ionic compound.
What is the anion present in compound R?
Correct Answer: \( \boxed{\mathrm{B}} \)
A white precipitate with \(\mathrm{Sr^{2+}}\) indicates the possible formation of insoluble \(\mathrm{SrSO_4}\) or \(\mathrm{SrCO_3}\).
Carbonate and hydrogencarbonate ions react with dilute nitric acid to release carbon dioxide gas, giving visible effervescence.
Since no visible reaction occurs with dilute \(\mathrm{HNO_3}\), the anion cannot be \(\mathrm{CO_3^{2-}}\) or \(\mathrm{HCO_3^-}\).
Sulfate ions form insoluble \(\mathrm{SrSO_4}\) but do not react with dilute nitric acid.
Therefore, the correct answer is (B).
Aqueous acid P and aqueous alkali Q have the same concentration.
\(20\,\mathrm{cm^3}\) of P is added to a conical flask.
Q is slowly added to the flask and the volume of Q and the pH are recorded.
The pH titration curve is shown.
Which row gives the identity of P and Q?
| P | Q | |
|---|---|---|
| A | HCl | NaOH |
| B | \(\mathrm{H_2SO_4}\) | \(\mathrm{NH_3}\) |
| C | HCl | \(\mathrm{Ba(OH)_2}\) |
| D | \(\mathrm{CH_3COOH}\) | \(\mathrm{Sr(OH)_2}\) |
Correct Answer: \( \boxed{\mathrm{C}} \)
The initial pH is close to \(0\), indicating that P is a strong acid.
The equivalence point occurs after about \(10\,\mathrm{cm^3}\) of alkali has been added, even though \(20\,\mathrm{cm^3}\) of acid was used.
Since both solutions have the same concentration, the alkali must provide twice as many hydroxide ions per mole as the acid provides hydrogen ions.
\(\mathrm{Ba(OH)_2}\) dissociates to give two \(\mathrm{OH^-}\) ions per formula unit, so only half the volume is required for neutralisation.
Therefore, P is \(\mathrm{HCl}\) and Q is \(\mathrm{Ba(OH)_2}\).
Therefore, the correct answer is (C).