1.8 - Halogens

physical properties of fluorine

yellow gas

Physical properties of chlorine

Yellow-green gas

Physical properties of bromine

Red-brown liquid

Physical properties of iodine

Grey black solid sublimes to purple vapour

Explain why there is an increase in mpt/bot as group 7 descended

RMM increases, more e- per molecule so stronger VDW forces between molecules so more energy needed

Are halogen molecules polar or non-polar?

non-polar

What happens to solubility of halogens in water down group 7?

decreases

What happens to Cl, Br and I in water?

Cl/Br slightly soluble, I almost insoluble

What are halogens also soluble in?

hexane(non-polar with weak VDW)

Chlorine colour in water/hexane

pale green/colourless, colourless

Bromine colour in water/hexane

yellow/orange/brown, red

Iodine colour in water/hexane

yellow/brown, purple

Chlorine + cold dilute NaOH reaction

Cl2 + 2NaOH = NaCl(aq) + NaClO(aq) + H2O

Chlorine with hot conc NaOH reaction

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

Bromine + cold dilute NaOH reaction

Br2 + 2NaOH = NaBr(aq) + NaBrO(aq) + H2O

Bromine + hot conc NaOH reaction

3Br2 + 6NaOH = 5NaBr(aq) + NaBrO3(aq) + 3H2O

Iodine and cold dilute NaOH reaction

I2 + 2NaOH = NaI(aq) + NaIO(aq) + H2O

Iodine and hot conc NaOH reaction

3I2 + 6NaOH = 5NaI(aq) + NaIO3(aq) + 3H2O

Chlorine + water reaction

Cl2 + H2O = HCl + HClO(aq)

decomposition of chloric acid

HClO = HCl + O

How is reaction of water and chlorine used in water sterilisation?

bacteria killed by oxidation caused by reactive O atoms produced by decomposition of HClO

Ozone products

O3 = O2 + O

Advantages of chlorine

cheaper than ozone, residual protection as stays in water

Disadvantages of chlorine

can’t kill all microorganisms, leaves chemicals

Advantages of ozone

kills more microorganisms, no residual chemicals

Disadvantages of ozone

more expensive, no residual protection

KBr + Chlorine colour change

colourless to orange

KBr + chlorine + hexane colour

orange/red

Displacement of halide ions by halogens experiment

add halogen to potassium halide soln, record colour, add hexane, stopper/shake, record colour

KI + Chlorine colour change

colourless to brown

KI + chlorine + hexane colour

purple

KI + Bromine colour change

colourless to brown

KI + bromine + hexane colour

purple

Chlorine + KBr equation

Cl2 + 2KBr = Br2 + 2KCl

Chlorine + KI equation

Cl2 + 2KI = I2 + 2KCl

Bromine + KI equation

Br2 + 2KI = I2 + 2KBr

Most powerful oxidising agent and why?

chlorine as it can displace other halogens from halide soln

How does oxidising ability of halogens change down group 7?

decreases as size increases down group so harder to accept e-

Reduction of H2SO4 by solid metal halides/hydrogen halides experiment

add spatula of NaCl to test tube, add conc H2SO4, warm in fume cupboard, record, repeat with Br/I

H2SO4 + NaCl observations

steamy/misty fumes, solid disappears, heat produced,

H2SO4 + NaCl products

HCl gas, NaHSO4

H2SO4 + NaBr observations

steamy/misty fumes, solid disappears, heat produced, red/brown vapour

H2SO4 + NaBr products

HBr gas, NaHSO4, SO2, Br gas

H2SO4 + NaI observations

steamy/misty fumes, violet/purple vapour, solid disappears, rotten egg smell, heat released, grey-black solid, yellow solid

H2SO4 + NaI products

HI gas, I gas/solid, S solid, NaHSO4, SO2, H2S

result for Cl- with H2SO4

steamy/misty fumes

result for Br- with H2SO4

red-brown vapour

result for I- with H2SO4

violet/purple vapour

NaF + H2SO4 equation

NaF + H2SO4 = NaHSO4 + HF

NaCl + H2SO4 equation

NaCl + H2SO4 = NaHSO4 + HCl

NaBr + H2SO4 (2 equations)

NaBr + H2SO4 = NaHSO4 + HBr, HBr + H2SO4 = Br2 + SO2 + 2H2O

NaI + H2SO4 (4 equations) - leave out H2SO4

NaI = NaHSO4 + HI, 2HI = I2 + SO2 + 2H2O, 6HI = 3I2 + S + 4H2O, 8HI = 4I2 + H2S + 4H2O