9701 · 11.4
The reactions of chlorine flashcards
Revision flashcards for Cambridge 9701 The reactions of chlorine (syllabus 11.4). Flip, recall, then mark a real past-paper question.
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What is disproportionation?
A redox reaction in which an element in a single species is simultaneously oxidised and reduced.
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What is the oxidation state of chlorine in Cl₂?
0, as it is an element in its standard state.
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What are the oxidation states of chlorine in the products of its reaction with water, HCl and HOCl?
-1 in HCl (reduction) and +1 in HOCl (oxidation).
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What is the systematic name for HOCl?
Chloric(I) acid. The (I) indicates the +1 oxidation state of chlorine.
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What is the systematic name for the ClO⁻ ion?
The chlorate(I) ion. It is sometimes also called the hypochlorite ion.
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Write the equation for the reaction of chlorine with water.
Cl₂(aq) + H₂O(l) ⇌ HCl(aq) + HOCl(aq). Note the equilibrium sign.
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Write the equation for the reaction of chlorine with cold, dilute aqueous sodium hydroxide.
Cl₂(aq) + 2NaOH(aq) → NaCl(aq) + NaClO(aq) + H₂O(l). This reaction goes to completion.
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What is the primary purpose of adding chlorine to drinking water?
To disinfect the water by killing pathogenic microorganisms like bacteria and viruses.
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Which chemical species is primarily responsible for the disinfecting action of chlorine in water?
Chloric(I) acid (HOCl), which is a more effective oxidising agent than the chlorate(I) ion (ClO⁻).
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What is a potential risk associated with the chlorination of drinking water?
The formation of small quantities of carcinogenic chlorinated hydrocarbons (e.g., trichloromethane, CHCl₃) from the reaction of chlorine with organic matter in the water.
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What are the products when chlorine reacts with hot, concentrated aqueous sodium hydroxide?
Sodium chloride (NaCl), sodium chlorate(V) (NaClO₃), and water. Chlorine is oxidised to a +5 state.
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What conditions are required for the reaction between chlorine and methane?
Ultraviolet (UV) light, which provides the energy for the homolytic fission of the Cl-Cl bond.