11.4 AS Level

The reactions of chlorine

11 flashcards to master this topic

Key Concept Flip

Describe the reaction of chlorine with cold, dilute aqueous sodium hydroxide, including oxidation numbers.

Answer Flip

Chlorine disproportionates: Cl₂ + 2NaOH → NaClO + NaCl + H₂O. The oxidation number of Cl changes from 0 in Cl₂ to +1 in NaClO and -1 in NaCl.

Key Concept Flip

Describe the reaction of chlorine with hot, concentrated aqueous sodium hydroxide, including oxidation numbers.

Answer Flip

Chlorine disproportionates: 3Cl₂ + 6NaOH → NaClO₃ + 5NaCl + 3H₂O. The oxidation number of Cl changes from 0 in Cl₂ to +5 in NaClO₃ and -1 in NaCl.

Key Concept Flip

Explain how chlorine is used in water purification. Include the relevant equation(s).

Answer Flip

Chlorine kills bacteria in water. Cl₂ + H₂O ⇌ HOCl + HCl. HOCl ⇌ H⁺ + ClO⁻. Both HOCl (hypochlorous acid) and ClO⁻ (hypochlorite ion) are active disinfecting agents.

Key Concept Flip

Explain why nitrogen is relatively unreactive.

Answer Flip

Nitrogen gas (N₂) is unreactive due to the strong triple bond (N≡N), which requires a large amount of energy to break. Additionally, the molecule is non-polar.

Definition Flip

Explain the basicity of ammonia using the Brønsted-Lowry theory.

Answer Flip

Ammonia (NH₃) is a Brønsted-Lowry base because it accepts a proton (H⁺) from an acid.

Example: NH₃ + HCl → NH₄⁺ + Cl⁻.
Key Concept Flip

Describe the structure of the ammonium ion (NH₄⁺) and its formation.

Answer Flip

The ammonium ion (NH₄⁺) has a tetrahedral shape with the nitrogen atom at the center. It forms when ammonia (NH₃) accepts a proton (H⁺) from an acid, using its lone pair of electrons to form a coordinate (dative covalent) bond.

Key Concept Flip

Explain how ammonia can be displaced from ammonium salts.

Answer Flip

Ammonia can be displaced from ammonium salts by a stronger base.

Example: heating an ammonium salt with a strong base like NaOH: NH₄Cl(s) + NaOH(aq) → NH₃(g) + NaCl(aq) + H₂O(l)
Key Concept Flip

Give examples of both natural and man-made occurrences of nitrogen oxides.

Answer Flip

Natural occurrences: Lightning strikes causing nitrogen and oxygen in the air to react. Man-made occurrences: Internal combustion engines and industrial processes at high temperatures.

Key Concept Flip

Describe the catalytic removal of nitrogen oxides (NOx) from exhaust gases.

Answer Flip

Catalytic converters use a catalyst (

Example: platinum, rhodium, palladium) to reduce NOx to nitrogen gas: 2NO → N₂ + O₂ and 2NO₂ → N₂ + 2O₂
Key Concept Flip

Describe how peroxyacetyl nitrate (PAN) is formed and its significance.

Answer Flip

PAN is formed when atmospheric nitrogen oxides (NO and NO₂) react with unburned hydrocarbons. It is a component of photochemical smog and a secondary pollutant, causing respiratory and eye irritation.

Key Concept Flip

Explain the role of NO and NO₂ in the formation of acid rain.

Answer Flip

NO and NO₂ dissolve in atmospheric moisture, forming nitrous and nitric acids, contributing directly to acid rain. They also act as catalysts in the oxidation of SO₂ to SO₃, which then forms sulfuric acid (H₂SO₄), a major component of acid rain.

Ready to test yourself?

Practice with MCQ questions to check your understanding of The reactions of chlorine.

Take Quiz
11.3 Some reactions of the halide ions 13.1 Formulas, functional groups and the naming of organic compounds