Chem topic 3 -> Halogens + qualitative tests

What is the trend in bp for halogens

• Bp increases down the group

• London forces get stronger as the molecules have more electrons → need more energy to be overcome → bp increases

What is the trend in reactivity for halogens

• Reactivity decreases down the group → nuclear charge increases but sheilding and atomic radius increases so nuclear attraction to the outermost electron decreases so it is harder for them to gain an electron

• Chlorine > Bromine > Iodine in terms of reactivity

• Can be tested using a displacement reaction → a halogen displaces a less reactive halogen from its compound

What are the colour changes for halogen displacement reactions in aqueous solution

What are the colour changes for halogen displacement reactions in organic solution

What is a disproportionation reaction

• When the same element is both oxidised and reduced

What are the uses of chlorine

• Chlorine + water → used to kill bacteria

• Chlorine + water is a disproportionation reaction

• Oxygen is both reduced and oxidised

• HCLO → sterilises water

• Chlorine + cold, dilute aqueous NaOH → produces NaClO → used as bleach

What is the test for Halide ions

• Add silver nitrate

• Chlorine → white precipitate

• Bromine → Cream precipitate

• Iodine → Yellow precipitate

Chlorine and Bromine precipitates look too similar

• Add dilute ammonia

• Chlorine’s white precipitate dissolves

• Bromine’s cream precipitate does not dissolve

To confirm the cream precipitate is bromine

• Add conc ammonia → dissolves

What is the test for carbonate ions

• Add HCl

• Fizzing/effervescense can be observed

• Attach a delivery bung to the test tube and bubble it thru limewater → turns cloudy

Test for sulfate ions

• Add Barium chloride

• Forms Barium Sulfate → white precipitate

Test for ammonium ions

• Add warm NaOH → forms ammonia gas

• turns damp red litmus paper blue