ES - Hydrogen halides Flashcards
What is a hydrogen halide?
A halogen + hydrogen.
How many electrons do all the halogens have in their outer shells?
7
How many electrons does hydrogen have in its outer shell?
1
How can hydrogen halides be made?
Using ionic halides.
How can hydrogen halides be made by using ionic halides?
By adding a concentrated acid, to a solid, ionic halide.
Usually phosphoric acid.
Why can’t you always use sulfuric acid to make hydrogen halides?
As it is an oxidising agent so it can get involved in redox reactions.
Why can’t sulfuric acid be used to make hydrogen bromide or hydrogen iodide?
When sodium bromide or sodium iodide for example, react with sulfuric acid, the bromide/iodide ions are oxidised to make bromine/iodine gas because bromine and iodine are strong enough reducing agents to reduce sulfuric acid.
When are hydrogen fluoride and hydrogen chloride stable?
When heated.
When heated, hydrogen fluoride and hydrogen chloride are stable, what does this mean?
They won’t split up into hydrogen and halide ions.
When heated, what happens to hydrogen bromide and hydrogen iodide?
They’ll split - hydrogen bromide slightly and hydrogen iodide more so.
When heated, why do hydrogen bromide and hydrogen iodide split?
Because of the strength of the hydrogen-halide bonds being weaker.
What happens to the strength of the hydrogen-halide bonds as you go down group 7?
They get weaker.
Why do the hydrogen-halide bonds get weaker down group 7?
Because the halogen atoms get bigger down the group, meaning the bonding electrons are further away from the nucleus and shielded by more inner electron shells.
Are hydrogen halides acidic or alkali?
Acidic.
Hydrogen chloride, hydrogen bromide and hydrogen iodide all dissolve in water to form what?
Strong acids.
What happens when a hydrogen halide dissolves in water?
It dissociates - the molecule splits apart to form 2 ions (a hydrogen ion and a halide ion).
What ion from hydrogen halides makes the solutions acidic?
The hydrogen ions.
What is an exception to the rule that hydrogen halides dissociate in water?
Hydrogen fluoride doesn’t fully dissociate in water (only a few molecules split apart) - still acidic but a weak acid.
What do all hydrogen halides react with?
Ammonia.
Why do hydrogen halides react with ammonia?
Ammonia is a base so can accept a proton to form the positively charged ammonium ion.
The ammonium ion can bond with a negative halide ion to produce an ammonium halide.
Why don’t all hydrogen halides react with sulfuric acid?
Hydrogen fluoride and hydrogen chlorine don’t react as they’re not strong enough reducing agents to reduce the sulfur.
Do all hydrogen halides react with ammonia?
Yes
Do all hydrogen halides react with sulfuric acid?
No
