ES6: Atom Economy + Hydrogen Halides Flashcards
Define “atom economy”
A measure of the proportion of reactant atoms that become desired products
What does atom economy indicate?
How much product and how much waste is produced
What does a reaction with a high atom economy mean?
The reaction is cheaper and more environmentally friendly
Equation for atom economy
sum of molar masses of desired products
sum of molar masses of all products
How do hydrogen halides form strong acids?
By dissolving in water
What is a strong acid?
An acid that will fully dissociate
What does “dissociating mean”?
The molecule splits apart to form:
- A H+ ion and a halide ion or
- An oxonium (H3O+ (aq) ion) and a halide ion
Which hydrogen halide is the only one to form a weak acid?
Hydrogen fluoride
How do hydrogen halides react with ammonia? Give an example formula with hydrogen fluoride
- Ammonia (NH3) accepts a proton to form a positive ammonium ion
- Ammonium ions bonds with a negative halide ion to produce an ammonium halide salt
E.g HF(aq) + NH3 (aq) ===> NH4F (aq)
What happens when hydrogen fluoride and hydrogen chloride are heated?
They are stable and so nothing occurs
What happens when hydrogen bromide is heated?
It splits slightly and some bromine gas is produced
What happens when hydrogen iodide is heated?
It splits strongly and large amounts of iodine gas is produced
What is the trend of thermal stability down Group 7?
It decreases
Why does thermal stability decrease down the group?
- The halogen atoms are bigger down the group
- So the bonding electrons are further from the nucleus and are shielded by more electron shells
- Therefore the strength of the hydrogen-halide polar covalent bond gets weaker
- Takes less energy to break
What can all hydrogen halides be formed by?
Using an ionic halide and concentrated phosphoric acid
Why can phosphoric acid be used to produce all hydrogen halides?
It is not an oxidising agent
Give the equation for phosphoric acid producing a hydrogen halide.
X- + H3PO4 ====> HX + H2PO4-
Which hydrogen halides can be made with concentrated sulfuric acid?
Hydrogen fluoride
Hydrogen chloride
Give the equation for sulfuric acid producing hydrogen chloride.
NaCl (s) + H2SO4 (aq) ====> NaHSO4 (aq) + HCl (aq)
Why can’t sulfuric acid produce hydrogen bromide?
- HBr- dissociates into Br- which is a strong reducing agent
- So it reduces sulphuric acid as it is oxidised to bromine gas
Give the equation for the reduction of sulfuric acid by Br-
H2SO4 + 2H+ + 2Br- ====> Br2 + SO2 + 2H20
Give the half equation for the reduction of Br-
2Br- ===> Br2 + 2e-
What is the gas made from the reaction between bromide ions and sulfuric acid a mixture of?
Sulfur dioxide, hydrogen bromide and bromine gas
Why can’t sulfuric acid produce hydrogen iodide?
- HI dissociates into I- which is a strong reducing agent
- Reduces sulphuric acid as it is oxidised to iodine gas
Do bromine or iodine ions reduce sulfuric acid more and why?
Iodine ions because they are a stronger reducing agent
Give the equation for the reduction of sulfuric acid by I-
H2SO4 + 8H+ + 8I- ====> 4I2 + H2S + 4H2O
What is the gas made from the reaction between iodine ions and sulphuric acid a mixture of?
- Hydrogen iodine
- Hydrogen sulphide
- Iodine gas
Do hydrogen fluoride and hydrogen bromine react with sulfuric acid and why?
No - they are not strong enough reducing agents
Give the equation for the reaction of hydrogen bromide with sulfuric acid.
2HBr + H2SO4 ====> SO2 + Br2 + 2H2O
Give the equation for the reaction of hydrogen iodine with sulfuric acid.
8HI + H2SO4 =====> 4I2 + H2S + 4H2O
