halogens

Electronegativity trend

Increase up group

Solubility

Low solubility in water cause non polar, dissolve easily in organic compounds

Chlorine colour in water

Colourless

Chlorine colour in hexane

Colourless

Bromide colour in water

Yellow / orange

Bromine colour in hexane

Orange / red

Iodine colour in water

Brown

Iodine colour in hexne

Pink / violet

Halogen reactivity

Get less reactive down the group, react by gaining electron in p orbital- reduced, but oxidise another substance (redox)- oxidising agents

Atoms become larger, outer electrons are futher from nucleus, shielded more from attraction, - also explains electronegative

Melting / boiling point down group

Increase

As you go down, more electron shells so stronger London forces

Harder to overcome intermolecular forces

Displacement

Where one element replaces another in a compound

Halogens relative oxidising strengths can be seen in displacement reactions

Chlorine displaces bromide and iodide

Bromide displaces iodide

Iodine will not displace chloride or bromide

Halogen halide reactions, redox

Chlorine and potassium bromides

Cl2 + 2e- → 2Cl- chlorine displaces bromine so is reduced

2Br- → Br2 + 2e- bromine is displaced by chlorine so gets oxidesed

Displacement of bromide colour change

Forms bromine, reaction mixture will turn orange

Iodide displacement colour change

Iodine formed so reaction mixture turns brown

Can mix w organic solvent like hexane, halogen dissolves and layer above aqueous solution

Reducing power of halides down the group

Halide = reducing agent

Ions get bigger so electrons are futher from nucleus + shielding

Reaction of KF or KCl with H2SO4

KF (s) + H2SO4 (l) → KHSO4 (s) + HF (g)

HF or HCl is formed, misty funes formed

F- or Cl- not strong enough reducing agents to reduce sulphuric acid so reaction stops there

Not a redox reaction, oxide numbers of halide and sulfur stay the same (-1 and +6)

Reaction of KBr w H2SO4

KBr (s) + H2SO4 (l) → KHSO4 (s) + HF (g)

Misty fumes

2HBr (aq) + H2SO4(l) → Br2 (g) + SO2 (g) + 2H2O (l)

Bromide ions are a stronger reducing agent than chloride ions react w H2SO4 in a redox reaction

Produces choking fumes of SO2 and orange fumes of bromine

Ox state of s: +6 → +4 reduction

Ox state of Br: -1 → 0 oxidation

Reaction of KI w H2SO4

KI (s) + H2SO4 (l) → KHSO4 (s) + HI (g)

2HI (g) + H2SO4 (l) → Br2 (g) + SO2 (g) + 2H2O (l)

Ox state of S: +6 → +4 reduction

Ox state of I: -1 → 0 oxidation

Stronger reducing agents, futher reduces to H2S

6HI (g) + SO2 (g) → H2S (g) + 3I2 (s) + 2H2O (l)

H2S smells of bad eggs

Ox state of S: +4 → -2 reduction

Ox state of I: -1 → 0 oxidation

Are hydrogen halides acid or alkali

Colourless gases, acidic

Can dissolve in water, produce misty fumes of acidic gas, turn damp blue litmus paper red

HCl (g) → H+ (aq) + Cl- (aq)

HCl (g) + H2O → H3O+ (aq) + Cl- (aq)

Hydrogen chloride- form hydrochloric acid, hydrogen bromide forms hydrobromic acid and hydrogen iodide gives hydroiodic acid

Hydrogen halides w ammonia

Hydrogen halides react w ammonia gas to give white fumes

NH3 (g) + HCl (g) → NH4CL (s) acid base reaction

How to test for halides

Add dilute nitric acid to remove ions which may interfere with reaction

Add silver nitrate solution AgNO3 (aq)

Silver and halide reaction

Ag+ (aq) + X- (aq) → AgX (s)

Precipitate colours w silver

Fluoride- AgF is soluble so no precipitate

Chloride- white

Bromide- cream

Iodide- yellow

How to make difference between colours clearer

Add ammonia solution

What does AgCl dissolve in

Dissolves in dilute ammonia solution to give a colourless solution

AgBr dissolving in ammonia

If dilute ammonia added- does not dissolve so stays the same

Will dissolve in conc ammonia solution to give a colourless solution

AgI

Precipitate does not dissolve even in conc ammonia solution

Test for carbonates

Carboates fizz, give off CO2

CO3-2 (s) + 2H+ (aq) → CO2 (g) + H2O (l)

Hydrogen carbonates also fizz- CO2

HCO3- (s) + H+ (aq) → CO2 (g) + H2O (l)

Test for CO2 using limewater- turns cloudy

Test for sulfates w hydrochloride acid and barium chloride

To identify sulfate ions (SO4 -2) Add dilute HCl followed by barium chloride solution

HCl removes carbonate ions before test

Ba+2 (aq) + SO4 -2 (aq) → BaSO4 (s)

White precipitate

How to test for ammonia compounds

Ammonia gas is alkaline so test w damp red litmus paper

Test for ammonium ions (NH4 +) add sodium hydroxide and heat

Do in fume cupboard

NH4+ + OH- → NH3 + H2O

Halogens reaction w group 1 and 2 metals

Oxidise gr 1 and 2 metals to produce halide salts

Eg 2Li (s) + F2 (g) → 2LiF (g)

Ox state of Li: 0 → +1 oxidised

Ox state if f: 0 → -1 reduction

Halogens and cold alkalis

Disproportionation

X2 + 2NaOH → NaOX + NaX + H2O

X2 + 2OH- → OX- + X- + H2O

Oxidation number of x: 0, +1, -1

Chlorine and sodium hydroxide

Form bleach

Chloride gas w cold dilute sodium hydroxide, forms sodium chlorate (1) solution- bleach

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

Ox number of Cl: 0. +1. -1

Used in water paper and t bleach textiles and cleaning

Halogens and ht alkalis

Also disproportionation

3X2 + 6NaOH → NaXO3 + 5NaX + 3H2O

3X2 + 6OH- → XO3- + 5X- + 3H2O

0 +5. -1

Chlorine in water

Mixing chorine and water, undergoes disproportionation, forms HCl and hypochlorous acid

Cl2 (g) + H2O (l) → HCl (aq) + HClO (aq)

0 ← -1 +1

Hypochlorous acid ionises to make chlorate ions (also called hypochlorite ions)

HCIO (aq) + H2O (l) → ClO- (aq) + H3O + (aq)

←

Adding chlorine to water can make it safe to drink or swim in