Group 7 (Halogens) Reactions

what is formed in the reactions between halogens and (some) metals

metal halide salts, which are ionic compounds consisting of halogen anions and metal cations.

what is happening to the metals when reacting with halogens

the metal is being oxidised, so halogens are acting as oxidising agents

how do halogens (chlorine, bromine and iodine) react with iron (II)

chlorine and bromine oxidise iron(II) to iron(III), while iodine has a lesser oxidising ability. iodine is oxidised from iodide ions to iodine

give the ionic equation of chlorine oxidising iron (II)

Cl2(g) + 2Fe2+(aq) → 2Cl-(aq) + 2Fe3+(aq)

give the ionic equation for the reaction between iodine and iron (III)

2I-(aq) + 2Fe3+(aq) → I2(aq) + 2Fe2+(aq)

give the equation for the reaction between chlorine and water

Cl2(g) + H2O(l) ↔ HCl(aq) + HOCl(aq)

give the equation for the reaction between cold sodium hydroxide and chlorine

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

give the equation for the reaction between hot, concentrated sodium hydroxide and chlorine

3Cl2(aq) + 6NaOH(aq) → NaClO3(aq) + 5NaCl(aq) + 3H2O(l)

how can the reducing power of halides be compared

by reacting them with concentrated sulphuric acid

what happens when a halide ion acts as a reducing agent

it loses electrons, given to the reduced species

what is the trend in reducing power down the group

reducing power increases down the group (I>Br>Cl>F)

why is sulphuric acid used to observe the reducing power of halides

as it can be reduced to many different oxidation states

what are the 4 species and their oxidation states containing sulphur

• H2SO4 → +6

• SO2 → +4

• S → 0

• H2S → -2

what happens during the test when concentrated sulphuric acid is added to solid samples of halide salts

NaX(s) + H2SO4(l) → HX(g) + NaHSO4(aq)

• acid-base reaction. concentrated acid means there are not many water molecules to fully dissociate, only one H+ ion is lost.

• HX(g) from reaction may reduce H2SO4 as gas bubbles through acid redox reaction where concentrated sulphuric acid acts as oxidising agent

what can the hydrogen halides (HBr, HCl and HI) be observed as

steamy fumes caused by HX gas reacting with water vapour in the air to produce a fog of concentrated HX acid

give the equation for the equation between NaCl and concentrated H₂SO₄ (1)

NaCl + H₂SO₄ → NaHSO₄ +HCl

what can be observed in the reaction between Cl^- ions and concentrated sulphuric acid

steamy fumes of HCl

give the equations between NaBr (Br- ions) and concentrated sulphuric acid (2)

NaBr + H2SO4 → NaHSO4 + HBr

2Br- + H2SO4 + 2H+ → Br2 + SO2 + 2H2O

what can be observed in the reaction of br- ions with concentrated sulphuric acid

• HBr - steamy fumes

• Br2 - brown fumes

• SO2 - colourless gas

give the equations for the reaction between NaI (I- ions) and concentrated sulfuric acid (4)

• NaI + H2SO4 → NaHSO4 + HI

• 2I- + H2SO4 + 2H+ → I2 + SO2 + 2H2O

• 6I- + H2SO4 + 6H+ → 3I2 + S + 4H2O

• 8I- + H2SO4 + 8H+ → 4I2 + H2S + 4H2O

what can be observed in the reaction between I- and concentrated H2SO4

• HI - steamy fumes

• I2 - purple fumes

• SO2 - colourless gas

• S - yellow solid

• H2S - gas (bad egg smell)

Give the balanced equation of the reaction between ammonia and hydrogen chloride

NH3(g) + HCl(g) ←→ NH4Cl(s)

What can be observed in the reaction between ammonia and hydrogen chloride

White smoke