Question
(a) Chlorine can be prepared using the following reaction.
MnO2(s) + 4HCl(aq) → MnCl2(aq) + 2H2O(l) + Cl2(g)
(i) Explain why MnO2(s) is described as an oxidising agent in this reaction.
Refer to oxidation numbers in your answer. (ii) State what you would observe during this reaction.
(b) The halogens chlorine, bromine and iodine are all volatile elements.
State and explain the trend in volatility down Group 17.
(c) Chlorine undergoes disproportionation during many chemical reactions.
(i) Write an equation for the reaction of chlorine with cold aqueous sodium hydroxide, NaOH.
Explain why it is a disproportionation reaction. (ii) One of the products of the reaction of chlorine with hot aqueous sodium hydroxide differs
from those in (c)(i).
Identify the compound that is formed in this reaction that is different from that formed in the
reaction in (c)(i).
(d) State and explain the use of chlorine in water purification.
(e) Under certain conditions, chlorine undergoes a free-radical substitution reaction with ethane.
(i) State the conditions required to initiate this reaction. (ii) Write the overall equation for this free-radical substitution reaction.
Answer/Explanation
Answer: (a)(i) It oxidises chlorine from –1 to 0
(a)(ii) effervescence / fizzing / bubbling OR
green gas formed
OR
solid dissolves / disappears / soluble
(b) M1: decreases (down the group)
M2: increasing induced dipoles
M3: greater number of electrons
(c)(i) M1: Cl2 + 2NaOH → NaCl + NaClO + H2O M2: chlorine is oxidised and reduced
(c)(ii) NaClO3 / sodium chlorate(V)
(d) M1: chloric(I) acid / hypochlorous acid / HClO
M2: kills bacteria / micro-organisms / microbes
(e)(i) ultra-violet (light) / sunlight
(e)(ii) C2H6 + Cl2 → C2H5Cl + HCl