Hydrogen halides - ES

Question 1

Properties of the hydrogen halides

Answer 1

all gases, made from covalent molecules, dissolve in water ionising to give give H⁺ and X⁺

Question 2

Solid halide salts react with conc sulphuric acid to give

Answer 2

white misty fumes of the hydrogen halide

Question 3

What is added to the solid halide salts for it to produce white misty fumes

Answer 3

conc sulphuric acid

Question 4

Halide salt and sulphuric acid equation

Answer 4

NaX₍ₛ₎ + H₂SO₄ ₍ₐq₎ -> NaHSO₄ ₍ₐq₎ + HX⁽g⁾

Question 5

Apparatus for making hydrogen halides

Answer 5

https://d1ymz67w5raq8g.cloudfront.net/Pictures/1024x536/3/2/2/511322_equipmentforpreparinghydrogenchloride_494363.jpg

Question 6

How to make HF and HCl

Answer 6

react halide salt with conc sulphuric acid

Question 7

Why can’t halide salt of Br and I reacted with sulphuric acid produce HBr and HI

Answer 7

as the halogens get less reactive down the group (worse at taking an electron and becoming halide ions). For the halide ions the trend is the other way : they get more reactive down the group (better at giving the extra electron, themselves getting oxidised). So they become more powerful reducing agents. Br⁻ and I⁻ are both powerful enough reducing agents to reduce sulphuric acid so an alternative reaction takes place

Question 8

What it the alternative reaction that takes place when a bromide salt reacts with sulphuric acid

Answer 8

2H⁺ + 2Br⁻ + H₂SO₄ -> SO₂₍₉₎+ Br₂₍ₗ₎ + 2H₂O₍ₗ₎

Question 9

For the alternative reaction that takes place when a bromide salt reacts with sulphuric acid what can you observe

Answer 9

HBr gas as white fumes, SO₂ gas and bromide vapour (brown) is given but pure HBr cannot be made this way

Question 10

What it the alternative reaction that takes place when a iodide salt reacts with sulphuric acid

Answer 10

8H⁺ + 8I⁻ + H₂SO₄ -> H₂S₍₉₎+ 4I₂₍ₗ₎ + 4H₂O₍ₗ₎

Question 11

For the alternative reaction that takes place when a iodide salt reacts with sulphuric acid what can you observe

Answer 11

HI gas as white fumes, H₂S gas (rotten egg smell), purple vapour of iodine gas but pure HI cannot be made this way

Question 12

How to make pure HI and HBr

Answer 12

use phosphoric acid instead of conc sulphuric acid because unlike sulphuric acid, conc phosphoric acid is not an oxidising agent so does not itself get reduced

Question 13

Chemical properties of hydrogen halides - Thermal stability

Answer 13

thermal stability decreases down the group as going down group 7 the strength of the H-X bond decreased because the halogen atom gets bigger so the bond is longer and weaker

Question 14

Chemical properties of hydrogen halides - Thermal stability - what happens to the hydrogen halides when heated

Answer 14

when heated HF and HCl are not broken down
Some HBr is broken down giving brown fumes of bromine gas (2HBr₍₉₎ -> H₂₍₉₎ + Br₂₍₉₎)
Most of HI breaks down giving large quantities of purple vapour
(2HI₍₉₎ -> H₂₍₉₎ + I₂₍₉₎)

Question 15

Chemical properties of hydrogen halides - Acidity

Answer 15

all the hydrogen halides dissolve well in water giving acidic solutions. HCl, HBr and HI fully ionise when in aqueous solution so they are strong acids
HCl -> H⁺ + Cl⁻

Question 16

Chemical properties of hydrogen halides - Reaction with ammonia

Answer 16

all hydrogen halides react with ammonia to give ammonia salts:
NH₃₍₉₎ + HCl₍₉₎ -> NH₄Cl₍ₛ₎
The ammonium slat is formed as tiny white particles which look like a white cloud - a good test for hydrogen halides

Question 17

Chemical properties of hydrogen halides - Reaction with conc sulphuric acid

Answer 17

HF and HCl do not react
HBr is powerful enough reducing agent to reduce H₂SO₄ to SO₂
HI is powerful enough reducing agent to reduce H₂SO₄ to H₂S