3.2.3 Group 7

What does fluorine exist as at room temp

pale yellow diatomic gas

What does chlorine exist as at room temp

green yellow diatomic gas

What does bromine exist as at room temp

orange brown liquid

What does iodine exist as at room temp

grey black solid, purple vapour

what is the trend in colour down group 7

darker

what colour solution does fluorine/chlorine make in water

colourless solution

what colour solution does bromine make in water

orange solution

what colour solution does iodine make in water

brown solution

Why does the volatility of the halogens decrease down the group

The amount of electrons in the molecule increases, so the VDW forces increase which makes it harder to separate molecules

Why does reactivity decrease down the group

The molecules gain an electron less easily as the outer shell is further from the nucleus meaning less attraction to the nucleus and more shielding

Why does MP/BP increase down the group

The amount of electrons in the molecule increases, so the VDW forces increase which makes it harder to separate molecules

Halogens are … agents

oxidising

Why does the oxidising power of the halogens decrease down the group

The electronegativity of halogens decreases down the group as the atomic radii increases, therefore there is more shielding between the outer shell and the nucleus, making it harder to accept an electron (oxidising agent)

How can the reactivity of the halogens be shown

displacement reactions where a more reactive halogen displaces a less reactive halogen from a compound

what reactant is the oxidising agent in a reaction between a halogen and a halide ion

the halogen element

Equation to show Cl2 displacing bromide

Cl2 + 2Br-  -> 2Cl- + Br2

Equation to show Cl2 displacing iodide

Cl2 + 2I-  -> 2Cl- + I2

Equation to show Br2 displacing iodide

Br2 + 2I- -> I2 + 2Br-

what is seen in the displacement reaction between chlorine and bromide and why

colourless to orange solution as bromine is formed

what is seen in the displacement reaction between chlorine and iodide and why

colourless to brown solution as iodine is formed

what is seen in the displacement reaction between bromine and iodide and why

orange to brown solution as iodine is formed

what can be used to distinguish between Br2 and I2 and why

cyclohexane can be shaken with the solution. the bottom layer will turn orange if Br2 is present and purple if I2 is present. the top layer is the organic layer

What agents do the halide ions act as

reducing agents

Why does the reducing power of the halides increase down the group

There are more electron shells, an increase in ionic radius and shielding so it is easier for the outer electron to be lost

How is the order of reducing ability of the halide ions shown

reaction with concentrated sulfuric acid

what is dangerous about the reactions between halides and concentrated sulfuric acid and how should this be controlled

they produce toxic gases so should be carried out in a fume cupboard

chloride + sulfuric acid equation, observation and type of reaction

NaCl + H2SO4 -> NaHSO4 + HCl, white misty fumes, acid-base

bromide + sulfuric acid equation, observation and type of reaction

NaBr + H2SO4 -> NaHSO4 + HBr, white misty fumes, acid-base

HBr and sulfuric acid equation, observation and type of reaction

2HBr + H2SO4 -> Br2 + SO2 + 2H2O, brown vapour, redox (H2SO4 is oxidising agent)

iodide + sulfuric acid equation, observation and type of reaction

NaI + H2SO4 -> NaHSO4 + HI, white misty fumes, acid-base

HI and sulfuric acid equation (to form SO2), observation and type of reaction

2HI + H2SO4 -> I2 + SO2 + 2H2O, purple vapour, redox (H2SO4 is oxidising agent)

HI and sulfuric acid equation (to form S), observation and type of reaction

6HI + H2SO4 - > 3I2 + S + 4H2O, yellow solid (sulfur), redox

HI and sulfuric acid equation (to form H2S), observation and type of reaction

8HI + H2SO4 - > 4I2 + H2S + 4H2O, gas smells of rotten eggs, redox

how are the halide ions identified

by adding silver nitrate (AgNO3)

Why is the silver nitrate acidified with nitric acid

to remove other ions eg carbonate that would give a false positive and so the nitrate ions stay present in solution

Chloride and silver nitrate half equation + observation

Ag+ (aq) + Cl- (aq) -> AgCl (s), white precipitate

Bromide and silver nitrate half equation + observation

Ag+ (aq) + Br- (aq) -> AgBr (s), cream precipitate

Iodide and silver nitrate half equation + observation

Ag+ (aq) + I- (aq) -> AgI (s), yellow precipitate

solubility of all silver precipitates when mixed with dilute ammonia (NH3)

AgCl soluble, AgBr and AgI insoluble.

solubility of all silver precipitates when mixed with concentrated ammonia (NH3)

AgCl and AgBr soluble, AgI insoluble

Why is chlorine added to drinking water, why is this dangerous but safe

to kill bacteria, only added in small amounts as it is toxic

Equation of reaction between chlorine and cold water (forms chlorate ions ClO-)

Cl2 + H2O -> ClO- + Cl- + H+

what type of reaction is the reaction between chlorine and cold water and why

disproportionation reaction as chlorine is both oxidised and reduced

what would happen if indicator was added to the reaction between chlorine and water and why

would turn red initially as H+ ions are acidic, then bleach as chlorate ions act as a bleach

equation to show decomposition reaction between chlorine and water in UV light

2Cl2 + 2H2O -> 4HCl + O2

How is bleach made?

By adding chlorine to cold, aqueous sodium hydroxide to produce sodium chlorate

Equation for bleach production

2NaOh + Cl2 -> NaClO + NaCl + H2O