Redox + Halogens

What are the physical states and colors of the halogens at room temperature?

Fluorine (F₂): Very pale yellow gas

Chlorine (Cl₂): Greenish gas

Bromine (Br₂): Red liquid (gives off brown/orange fumes)

Iodine (I₂): Shiny grey solid (sublimes to purple gas)

Why do melting and boiling points increase down Group 7?

Larger molecules have more electrons → stronger van der Waals forces; More energy is needed to overcome these forces.

How does electronegativity change down Group 7? Why?

Decreases down the group; Atomic radius increases → weaker nuclear attraction for bonding electrons.

Which halogens can displace others? Give an example equation.

Stronger oxidisers (higher up) displace weaker ones; Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂; Br₂ displaces I⁻

What are the observations for halide ions with AgNO₃?

Cl⁻: White precipitate (AgCl) – dissolves in dilute NH₃

Br⁻: Cream precipitate (AgBr) – dissolves in conc. NH₃

I⁻: Pale yellow precipitate (AgI) – insoluble in NH₃

What are the reactions of NaBr and NaI with conc. H₂SO₄?

NaBr: HBr (white fumes), SO₂ (colorless gas), Br₂ (orange fumes)

NaI: HI (white fumes), I₂ (black solid/purple fumes), SO₂, S, H₂S (bad egg smell)

What is the disproportionation reaction of chlorine in water?

Cl₂ + H₂O ⇌ HClO + HCl; Uses: Bleach (HClO) and water treatment.

Name these compounds using IUPAC: NaClO, NaClO₃, K₂SO₃.

NaClO: Sodium chlorate(I); NaClO₃: Sodium chlorate(V); K₂SO₃: Potassium sulfate(IV)

How does oxidising strength change down Group 7?

Decreases down the group; Fluorine (F₂) is the strongest oxidizer; iodine (I₂) the weakest; Example: Cl₂ oxidizes Br⁻ and I⁻, but Br₂ only oxidizes I⁻

Why is nitric acid added before AgNO₃ in halide tests?

Removes CO₃²⁻ ions to prevent false positives (e.g., Ag₂CO₃ precipitate); Reaction: 2HNO₃ + Na₂CO₃ → 2NaNO₃ + H₂O + CO₂

Why does reducing power increase down Group 7?

Larger ions (e.g., I⁻) donate electrons more easily due to: Increased atomic radius; Weaker nuclear attraction for outer electrons

What are the observations when NaF/NaCl reacts with conc. H₂SO₄?

NaF: White steamy fumes (HF gas); NaCl: White steamy fumes (HCl gas)

No redox – only acid-base reactions occur

Write the overall redox equation for NaBr + H₂SO₄.

2NaBr + 3H₂SO₄ → 2NaHSO₄ + SO₂ + Br₂ + 2H₂O

Observations: White fumes (HBr), Orange fumes (Br₂), Colorless gas (SO₂)

List all products when NaI reacts with conc. H₂SO₄.

HI (white fumes), I₂ (black solid/purple fumes), SO₂ (colorless gas), S (yellow solid), H₂S (bad egg smell gas)

What happens when chlorine water is exposed to sunlight?

2Cl₂ + 2H₂O → 4H⁺ + 4Cl⁻ + O₂

Observations: Greenish color fades (Cl₂ consumed), Colourless gas (O₂) produced

What is the product of Cl₂ + cold dilute NaOH?

Cl₂ + 2NaOH → NaCl + NaClO + H₂O

Uses: NaClO is a bleach/bactericide

What colors indicate free halogens in solution?

Cl₂(aq): Very pale green (often colorless)

Br₂(aq): Yellow

I₂(aq): Brown (may have black solid)

Write the half-equation for Br⁻ oxidation by Cl₂.

2Br⁻ → Br₂ + 2e⁻

Full equation: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂