halogens: content

Question 1

basic properties of halogens

Answer 1

very reactive
nonmetals
seven valence electrons (gain one electron when ionised)
exist as (nonpolar) diatomic molecules
toxic

Question 2

appearance of room temperature F₂

Answer 2

pale yellow GAS

Question 3

appearance of room temperature Cl₂

Answer 3

pale green GAS

Question 4

appearance of room temperature Br₂

Answer 4

dark red/orange LIQUID

Question 5

appearance of room temperature I₂

Answer 5

dark purple/black SOLID

Question 6

how does the oxidising ability of halogens change going down group seven

Answer 6

DECREASES as they become less reactive
(atomic radius increases, shielding increases, weaker nuclear attraction)

Question 7

test for how oxidising ability changes going down group seven

Answer 7

DISPLACEMENT REACTIONS
aqueous halogen solutions are added to aqueous halide salts, giving a colour change

organic solvents (eg hexane) are added to make the colour change easier to see: the halogen dissolves in these and sits as a layer above the solution

Question 8

group seven oxidising ability: Cl₂ in KBr
observations and ionic equation

Answer 8

aqueous layer: yellow Br₂ solution
organic layer: orange Br₂ solution

Cl₂ + 2Br⁻ → Br₂ + 2Cl⁻
chlorine is more reactive than bromine as it has displaced the bromide ions from the potassium salt

Question 9

group seven oxidising ability: Cl₂ in KI
observations and ionic equation

Answer 9

aqueous layer: brown I₂ solution
organic layer: purple I₂ solution

Cl₂ + 2I⁻ → I₂ + 2Cl⁻
chlorine is more reactive than iodine as it has displaced the iodide ions from the potassium salt

Question 10

group seven oxidising ability: Br₂ in KI
observations and ionic equation

Answer 10

aqueous layer: brown I₂ solution
organic layer: purple I₂ solution

Br₂ + 2I⁻ → I₂ + 2Br⁻
bromine is more reactive than iodine as it has displaced the iodide ions from the potassium salt

Question 11

group seven oxidising ability: observations if iodine added to aqueous (potassium) halide solution

Answer 11

none! iodine is the least reactive halogen so no displacement reaction would occur so we would see nothing

Question 12

trends in oxidising power of halogen atoms

Answer 12

strongest
fluorine
chlorine
bromine
iodine
weakest

Question 13

test for halide ions
full + ionic equations

Answer 13

acidified silver nitrate and ammonia
precipitate reaction
AgNO₃ + NaX → AgX + NaNO₃
Ag⁺ (aq) + X⁻ (aq) → AgX (s)

Question 14

halide test observations: F⁻ Cl⁻ Br⁻ I⁻ with silver nitrate

Answer 14

F⁻ AgF is soluble: no visible change
Cl⁻ white ppt
Br⁻ cream ppt
I⁻ yellow ppt