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)

Trend in melting and boiling points in Group 7? Why?

Increase down group.

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 and shielding increases → weaker nuclear attraction for bonding electrons.

Oxidising agent strength down group 7? Why?

Decreases down the group

Electronegativity decreases down group —> weaker nuclear attraction for bonding pair of electrons

Reducing agent strength down group 7? why?

Increases down group

Larger ions (e.g., I⁻) accept electrons more easily due to:

Increased atomic radius; Weaker nuclear attraction for bonding pair of electrons

What colors indicate free halogens in solution?

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

Br₂(aq): Yellow

I₂(aq): Brown (may have black solid)

Which halogens can displace others? Give an example equation.

Stronger oxidising agents (higher up) displace weaker ones;

e.g. Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

Br₂ displaces I⁻

Test for halide ions? Observations? Solubilities in NH3?

HNO3 followed by AgNO3 solution

F⁻: No ppt

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

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

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

Why is nitric acid added before AgNO₃ in halide tests?

Removes CO₃²⁻ ions to prevent false positives (e.g., Ag₂CO₃ precipitate)

which product is always formed in acid-base step of reaction of Na(halide) + H2SO4? whats the colour of it? how do you know when it is only an acid-base reaction and no redox has occurred?

NaHSO4 (white solid)

only acid-base when there is no change in oxidation numbers

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

NaF(s) + H2SO4 (l) —> NaHSO4 (s) + HF(g)

Observations: White steamy fumes of HF are evolved.

NaCl(s) + H2SO4 (l) —> NaHSO4 (s) + HCl(g)

Observations: White steamy fumes of HCl are evolved.

No redox – only acid-base reactions occur

two types of reactions that take place when NaBr/NaI react with H2SO4?

acid-base reaction

redox reaction

acid-base reaction of NaBr/NaI with H2SO4? observations?

NaBr(s) + H2SO4 (l) —> NaHSO4 (s) + HBr(g)

white steamy HBr fumes evolved

NaI(s) + H2SO4 (l) —> NaHSO4 (s) + HI(g)

white steamy HI fumes evolved

Br- oxidation half equation?

H2SO4 reduction half equation?

combined redox equation?

ox: 2Br- —> Br2 + 2e-

red: H2SO4 + 2H+ + 2e- —> SO2 + 2H2O

2H+ + 2 Br- + H2SO4 —> Br2 (g) + SO2 (g) + 2H2O(l)

orange fumes of Br2, colourless + acidic SO2

overall redox equation for NaBr + H₂SO₄? (COMBINE ACID-BASE REACTION WITH REDOX REACTION)

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

Observations: White steamy fumes (HBr), Orange fumes (Br₂), Colourless acidic gas (SO₂)

I- oxidation half equation? NaI(s) + H2SO4 (l) —> NaHSO4 (s) + HI(g)

H2SO4 half equations?

combined redox equations?

ox: 2I- —> I2 + 2e-

red1: SO₄²⁻ + 4H⁺ + 2e⁻ → SO₂ + 2H₂O

red2: SO₄²⁻ + 8H⁺ + 6e⁻ → S + 4H₂O

red3: SO₄²⁻ + 10H⁺ + 8e⁻ → H₂S + 4H₂O

comb1: 2I- + H2SO4 + 2H+ —> I2 + SO2 + 2H2O

comb2: 6I- + H2SO4 + 6H+ —> 3I2 + S + 4H2O

comb3: 8I- + H2SO4 + 8H+ —> 4I2 + H2S + 4H2O

white steamy HI fumes, black solid + purple I2 fumes, colourless + acidic SO2 gas, yellow solid S, H2S gas (bad egg smell)

overall redox equations for NaI + H2SO4? (COMBINE ACID-BASE REACTION WITH REDOX REACTIONS)

2NaI + 2H₂SO₄ → I₂ + SO₂ + 2H₂O + 2NaHSO₄

6NaI + 4H₂SO₄ → 3I₂ + S + 4H₂O + 6NaHSO₄

8NaI + 5H₂SO₄ → 4I₂ + H₂S + 4H₂O + 8NaHSO₄

definition of disproportionation?

disproportionation reaction of chlorine in water? uses of product?

reaction where an element simultaneously oxidises and reduces.

Cl₂ + H₂O ⇌ HClO + HCl

Cl2 used in water treatment to kill bacteria

HClO - bleach

What happens when chlorine water is exposed to sunlight?

2Cl₂ + 2H₂O → 4H⁺ + 4Cl⁻ + O₂

Observations: Greenish colour of the water fades as Cl₂ reacts, Colourless gas (O₂) produced

What is the product of Cl₂ + cold dilute NaOH?

Cl₂(aq) + 2NaOH(aq) → NaCl(aq) + NaClO(aq) + H₂O(l)

Uses: NaCl and NaClO is used as bleach and to kill bacteria