18 Halogens

What is the physical state and colour of chlorine (Cl2) at RTP

Pale green gas

What is the physical state and colour of Bromine (Br2) at RTP

Red-brown liquid

What is the physical state and colour of Iodine (I2) at RTP

Grey-black solid

What colour is iodine in an organic solvent like cyclohexane?

Violet / purple

What colour is bromine in Aq solution

Orange/yellow

Explain the BP down group 7

• Increases BP as you go down group 7

• Due to more electrons

• Means that London forces become steonger

• More energy to break these intermolecular FORCES

NOT BONDS!

Explain the trend in reactivity down group 7

• Reactivity decreases

• Atomic radius and electron shielding increases

• Nuclear attraction decreases

• Harder to gain an electron

What is observed when Cl2 is mixed with Br- (Chlorine and BromIDE) - give ionic equation

Cl2 + Br- → 2Cl- + Br2

Colourless to orange

Colour change and observation when Cl2 and I- - ionic equation

Colourless to brown

Cl2 + 2I- → 2Cl- + I2

When adding organic layer, turns purple

Colour change and observation of Br2 and I-

Br2 + 2I- → 2Br- + I2

Orange to brown

If organic layer added - Purple

Define disproportionation

A Reaction where the same element is simultaneously oxidised and reduced

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

• Cl changes from 0 to +1 in HClO and -1 in HCl

Chlorine reacting with cold dilute NaOH

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

Sodium chlorate (I) Bleach

Chlorate (ClO-)

Benefits and risk of adding chlorine to drinking water

+ kills harmful bacteria

- Chlorine is toxic/ reacts with organic matter to form chlorinated hydrocarbons in which is cancerous

Reagent used fir halide tests and its precipitate colours

AgNO3 silver nitrate (V)

Cl- : white, dissolves in dilute NH3

Br-: cream, insoluble in dilute NH3, dissolves in conc dilute NH3

I- : yellow, Insoluble in both dilute and conc NH3

Test for ammonium and its observations

Sodium hydroxide and warmed gently

Gas produced makes damp red litmus paper blue (ammonia gas, NH3)

Compare oxidising and reducing agents in halides

Oxidising: decreasing down, atoms has more shielding, making it harder to gain an e-

Reducing: increases as you go down the group, with more shielding, which is easier to lose an outer e-

Carbonate test

• dilute nitric acid HNO3

• present: bubbling

Sulfate test

Dilute barium chloride or barium nitrate

BaCl2 / Ba(NO3)2

• precipitate