Summary
Chlorine undergoes disproportionation reactions with both cold and hot aqueous sodium hydroxide, where it is simultaneously oxidized and reduced. Chlorine is also used in water purification due to its ability to kill bacteria and other microorganisms.
- Disproportionation Reaction — a reaction where an element is simultaneously oxidized and reduced. Example: Chlorine reacts with sodium hydroxide to form chloride and chlorate ions.
- Oxidation State — a number representing the total number of electrons an atom gains or loses. Example: In Cl2, chlorine has an oxidation state of 0, which changes in reactions with NaOH.
- Hypochlorous Acid (HOCl) — a weak acid formed when chlorine reacts with water. Example: HOCl dissociates into H+ and OCl- ions, acting as a disinfectant.
Exam Tips
Key Definitions to Remember
- Disproportionation Reaction
- Oxidation State
- Hypochlorous Acid (HOCl)
Common Confusions
- Confusing the oxidation states of chlorine in different reactions
- Misunderstanding the role of chlorine in water purification
Typical Exam Questions
- What happens when chlorine reacts with cold aqueous sodium hydroxide? It forms NaCl, NaClO, and water through a disproportionation reaction.
- How does chlorine purify water? Chlorine reacts with water to form HOCl, which kills bacteria.
- What are the oxidation states of chlorine in its reaction with hot NaOH? Chlorine is reduced to -1 and oxidized to +5 and +7.
What Examiners Usually Test
- Understanding of disproportionation reactions
- Ability to identify changes in oxidation states
- Knowledge of chlorine's role in water purification