Halogens Flashcards
What is the order of reducing powers for halides?
F- < Cl- < Br- < I-
Why does reducing power of halides increase down the group?
Because of increasing atomic radius and increasing shielding down the groups
Adding conc. sulphuric acid to a solid halide (NaCl)
NaCl + H₂SO₄ ——> NaHSO₄ +
HCl
- acid-base reaction
- Cl- can’t reduce H₂SO₄
Adding conc. H₂SO₄ to NaBr
NaBr + H₂SO₄ ——> NaHSO₄ + HBr
HBr + H₂SO₄ ——> Br2 + SO ₂ + 2H2O
Redox, Br- reduced (S in) sulphuric acid to sulphur dioxide
Describe and explain the trend in electronegativity
- decreases
- higher atomic radius = bigger atom = more shielding = weaker attraction between nucleus and e- in covalent bond
Describe and explain the trend in boiling point down the group
- increases
- molecules get bigger, more van der waals forces which require more energy to overcome
Oxidising power of halogens
Cl > Br > I
Observations of halides as reducing agents
NaCl- Misty fumes
NaBr- Misty fumes, SO2 (choking gas), Br2 (orangey Brown vapour)
NaI, Misty fumes, SO2 (choking gas), S (yellow powder), H2S (bad egg smell), I2 (purple vapour)
What is disproportionation
Same species has simultaneously has been oxidised and reduced
Displacement reactions of halogens
Cl₂ + 2Br⁻ ——> 2Cl⁻ + Br₂ (yellow solution)
Cl₂ + 2I⁻ ——–> 2Cl⁻ + I₂ (brown solution)
Br₂ + 2I⁻ ———> 2Br⁻ + I₂ (brown solution)
Observations when silver nitrate is added to halides
AgCl- white precipitate
AgBr- cream precipitate
AgI- yellow precipitate
Chlorine reaction to form chlorine water
Cl₂ (g) + H₂O (l) ⇌ HCl (aq) + HClO (aq)
Dissolving Cl₂ in NaOH (cold and dilute)
Cl₂ (g) + 2NaOH ⇌ H₂O + NaCl + NaClO
Chlorine exposed to sunlight
dark Cl₂ + H₂O ⇌ HCl + HClO
sunlight Cl₂ + H₂O ⇌ 2HCl + 1/2 O₂
Why is chlorine added to drinking water?
To remove bacteria
