Reaction With Water and Alkali (school)
Chlorine reacts with water to give a mixture of HCl and HClO (HOCl), an acidic solution that can bleach damp litmus.
Learning objectives
- Explain Reaction with Water and Alkali (school) using Group 17 language.
- Link trends to size, shielding, forces and bond strength.
- Apply equations and observations in FBISE-style answers.
Definition
Chlorine reacts with water to give a mixture of HCl and HClO (HOCl), an acidic solution that can bleach damp litmus. With cold dilute alkali, chlorine disproportionates: Cl₂ + 2NaOH → NaCl + NaClO + H₂O, with oxidation states 0 → −1 and 0 → +1. Hot concentrated alkali gives different chlorate products in the school naming story.
Core Concept
Water: Cl₂ + H₂O ⇌ HCl + HClO (HOCl) · acidic · bleaches damp litmus Cold dilute alkali (disproportionation): Cl₂ + 2NaOH → NaCl + NaClO + H₂O Cl: 0 → −1 (Cl⁻) and 0 → +1 (ClO⁻) Hot conc. alkali: chloride + chlorate(V) named (ClO₃⁻) — equation names for exams, not a factory.
Beginner
Cl₂ in water → HCl + HOCl; solution acidic; can bleach litmus. Cl₂ in cold dilute NaOH → salt NaCl + bleach-type NaClO + water. Same Cl atoms go to −1 and +1 — that is disproportionation.
Intermediate
Write the cold dilute equation and show oxidation states 0 → −1 and 0 → +1. Name HClO/HOCl and ClO⁻. Mention hot conc. products only as named ClO₃⁻ chemistry. Stress “names/equations only”.
Advanced
Disproportionation is a redox reaction of a single element into two oxidation states. Track Cl carefully: elemental Cl₂ is neither Cl⁻ nor ClO⁻ until reaction. Water equilibrium vs alkali product set are different conditions — do not mix equations.
Remember
Cl₂+H₂O⇌HCl+HClO · cold dilute: Cl₂+2NaOH→NaCl+NaClO+H₂O · 0→−1 and 0→+1 · disproportionation · not a factory.
Exam preparation
Exam Focus
Quick revision
Revision Zone
Reaction With Water and Alkali (school)
Sticky Notes · Quick Revision
With water
- HCl + HClO (HOCl)
- Acidic solution
- Bleaches damp litmus
Cold dilute alkali
- Cl₂ + 2NaOH → NaCl + NaClO + H₂O
- Disproportionation
- 0 → −1 and 0 → +1
Hot conc. (named)
- Chloride + chlorate(V)
- ClO₃⁻ named
- Different from cold
Exam discipline
- Equations/names only
- No plant SOP
- Track oxidation states
60-second revision
- Water: Cl₂ ⇌ HCl + HClO; acidic; bleaching litmus.
- Cold dilute NaOH: NaCl + NaClO + H₂O; disproportionation 0→−1/+1.
- Hot concentrated alkali: chlorate(V) named — different products.
Did you understand this topic?
Your answer is saved with your learning record. It does not mark the topic as mastered.