(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.
Explanation
(a)(i) A labelled diagram for the laboratory preparation of a dry, sample of sulphur (iv) oxide.
(Any one situable but must correspond to reactants in the diagram)
(ii) Balanced chemical equation for the reaction in 4(a)(i)
NaSO\(_{3(aq)}\) + 2HCl\(_{(aq)}\) —> 2NaCl\(_{3(aq)}\) H2O\(_{(l)}\) + SO\(_{2(g)}\)
OR
K\(_{2}\)SO\(_{3(aq)}\) + 2HCl\(_{(aq)}\) —> H\(_2\)O\(_{l}\) + SO\(_{2(g)}\)
OR
NaSO\(_{3(aq)}\) + H\(_2\)SO\(_{4(aq)}\) —> 2Na\(_{2}\)SO\(_4\) + H\(_2\)O\(_{(l)}\) + SO\(_{2(g)}\)
(iii) Precaution in the preparation of the gas in 4(a)(i). The gas should be prepared in a fume cupboard (chamber).
(iv) Reason for the precaution. It is because the gas is poisonous.
(b)(i) Dalton's law of partial pressures states that for a mixture of gases which do not react, the total pressure is equal to the sum of the partial pressures of the individual gases.
(ii) Volume of methane (CH\(_4\)) collected over water at temperature of 12°C and a pressure of 700mmHg was 30cm\(_3\).
Volume of the gas (dry) at s.t.p.
\(\frac{P_1V_1}{T_1} = \frac{P_2 V_2}{T_2}\)
\(P_1\) = (700 — 10) = 690 mmHg (dry gas)
\(T_1\) = 12 + 273 = 285 K
\(V_2\) = \(\frac{P_1V_1T_2}{P_2T_1}\)
P\(_2\) = 760mmHg, T\(_2\) = 273k
\(V_2\) = \(\frac{690 \times 30 \times 273}{760 \times 285}\)
\(V_2\) = 26.09cm\(^3\)
\(V_2\) = 26.10cm\(^3\)
(c)(i) Equation for the reaction between chlorine and water. Cl\(_{2(g)}\) + H\(_2\)O \(\to\) HCI + HCIO
(ii) Litmus paper turned red (from blue to red) because H\(^+\) ions are released or HCI produced is acidic. Also HCIO produced is acidic too. The solution is acidic.
(d)(i) Trend in the boiling points of chlorine, bromine and iodine. Boiling point of iodine is greater than that of bromine which is greater than that of chlorine. Boiling point increases from chlorine to iodine.
(ii) Water has a higher boiling point than ammonia because water has stronger hydrogen bonds than ammonia. Also because oxygen atom has two lone pairs of electrons and nitrogen atom has one pair of electron. Also oxygen is more electronegative than nitrogen.