(a)(i) Draw and label a diagram for the laboratory preparation of a dry sample of sulphur(IV)oxide. (ii) Write a balanced chemical equation for the reaction...
Question 1 Report
(a)(i) Draw and label a diagram for the laboratory preparation of a dry sample of sulphur(IV)oxide.
(ii) Write a balanced chemical equation for the reaction in (a)(i).
(iii) State the precaution that must be taken in the preparation of the gas stated in (a)(i).
(iv) Give a reason why the precaution stated in (a)(ii) must be taken.
(b)(i) State Dalton's law of partial pressures.
(ii) The volume of a sample of methane collected over-water at a temperature of 12°C and a pressure of 700 mmHg was 30cm\(^3\). Calculate the volume of the dry gas at s.t.p. [Saturated vapour pressure of water at 12°C is 10 mmHg] •
(c)(i) Write an equation for the reaction between chlorine and water.
(ii) Why does litmus paper turn red when put in the resulting solution in (c)(i)?
(d)(i) State the trend in the boiling points of chlorine, bromine and iodine.
(ii) Explain briefly why water has a higher boiling point than ammonia.
Answer Details
(a)(i) The apparatus for preparing and drying sulphur(IV) oxide is shown below.
(ii)
\[\mathrm{Na_2SO_3(aq)+2HCl(aq)\rightarrow 2NaCl(aq)+H_2O(l)+SO_2(g)}\]
(iii) The preparation should be carried out in a fume cupboard.
(iv) Sulphur(IV) oxide is poisonous and irritates the eyes and respiratory tract; the fume cupboard prevents inhalation of the gas.
(b)(i) Dalton's law of partial pressures states that the total pressure of a mixture of non-reacting gases is equal to the sum of the partial pressures of the individual gases.
(ii)
The methane was collected over water, so its pressure is:
\[P_1=700-10=690\ \mathrm{mmHg}\]
\[T_1=12+273=285\ \mathrm{K}\]
At s.t.p., \(P_2=760\ \mathrm{mmHg}\) and \(T_2=273\ \mathrm{K}\).
Using \(\dfrac{P_1V_1}{T_1}=\dfrac{P_2V_2}{T_2}\):
\[V_2=\frac{P_1V_1T_2}{P_2T_1}=\frac{690\times30\times273}{760\times285}=26.1\ \mathrm{cm^3}\]
Therefore, the volume of dry methane at s.t.p. is \(26.1\ \mathrm{cm^3}\).
(c)(i)
\[\mathrm{Cl_2(g)+H_2O(l)\rightleftharpoons HCl(aq)+HClO(aq)}\]
(ii) Hydrogen chloride, \(\mathrm{HCl}\), ionises in water to produce \(\mathrm{H^+}\) ions. The resulting solution is acidic and turns blue litmus paper red.
(d)(i) The boiling points increase from chlorine to iodine:
\[\mathrm{Cl_2<Br_2<I_2}\]
(d)(ii) Water has a higher boiling point because its intermolecular hydrogen bonding is stronger and more extensive than that in ammonia. Oxygen is more electronegative than nitrogen, and each water molecule can form more hydrogen bonds; hence more energy is required to separate water molecules.
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