NEW ES Flashcards
Formula for atom economy
Mr of desired products/ mr of reactants x100
Why is it desirable to have a high atom economy?
Little or no waste product meaning the process is more economically viable.
Redox
Oxidation (loss of electrons) and Reduction (gain of electrons)
What is an oxidising agent?
Accepts electrons from species being oxidised. It gains electrons and gets reduced
What is an oxidising agent?
Accepts electrons from species being oxidised. It gains electrons and gets reduced
What is a reducing agent?
Donates electrons to the species getting reduced. Loses electrons and gets oxidised.
What is electrolysis?
The decomposition of molten or aq ionic compound (an electrolyte) by passing an electric current through it. Solution must contain a cathode (neg electrode) and an anode (positive electrode).
What is electrolysis?
The decomposition of molten or aq ionic compound (an electrolyte) by passing an electric current through it. Solution must contain a cathode (neg electrode) and an anode (positive electrode).
What happens if the metal ions are below hydrogen in the electrochemical series using inert electrodes?
Metal atoms will be produced at the cathode.
What happens if the metal is above hydrogen in the electrochemical series using inert electrodes?
Hydrogen gas will be produced at the cathode
What happens typically when a solution is oxidised using inert electrodes?
Oxygen is produced at the anode but if conc chloride ions are present then chlorine will form.
Electrolysing with non-inert cathodes?
Same reaction at cathode but at the anode atoms in the anode loose electrons to form ions in the electrolyte. Net charge is a transfer of an element from the anode to cathode.
What group of the periodic table are the halogens in?
7
The 4 stages of extraction of bromine from the sea:
- Oxidation of Br- to Br2
Water is first acidified using sulphuric acid to sop the halogens reacting with water as this would lead to a loss of bromine product.
Excess chlorine used to displace bromine
Ox st of chlorine changed from 0 to -1. Ox st of bromine changes from -1 to 0. - Bromine vapours removed
- Reduction of Br2 to HBr
Sulphur dioxide, water and bromine vapours react to form hydrogen bromide- much more conc then bromine in seawater. - Oxidation of hydrogen bromide to bromine
Steam and chlorine used.
Bromine dried using conc sulfuric acid.
What is fluorine?
Pale yellow gas
What is chlorine?
Pale green gas
What is Bromine?
Red/ brown liquid
What is iodine?
Dark grey solid which sublimes to purple vapour
Volatility of halogens
Decreases down the group as the boiling point increases. Highlighted by physical state
Colour of chlorine in water
Green
Colour of bromine in water
Orange/ red
Colour of iodine in water
Brown
What is the reactivity like of halogens?
When halogens react they gain an electron. As their atomic radius increases this becomes harder as the positive attraction of the nucleus is weakened by additional shielding. Reactivity decreases down the group.
Oxidising power of the halogens
Decreases down the group as their ability to attract electrons decreases due to shielding and a greater atomic radius
Chlorine + bromide ions
Colourless to orange
Chlorine + iodide ions
Colourless to brown
Bromine + iodide ions
Orange to brown
What happens when halide ions react with acidified silver nitrate?
They react to form different coloured precipitates.
Silver nitrate+ chloride ions
WHITE precipitate
Silver nitrate + Bromide ions
CREAM precipitate
Silver nitrate + iodide ions
YELLOW precipitate
How is HCl prepared?
Using concentrated phosphoric acid and a solid chloride like sodium chloride. Phosphoric acid donates a hydrogen ion to the chloride ion to make hydrogen chloride which is a gas. Method is used to make hydrogen bromide and hydrogen iodide.
What can sulfuric acid be used to make?
Hydrogen chloride but not hydrogen bromide or iodide because sulfuric acid is a good oxidising agent and would further oxidise hydrogen bromide and iodide to bromine and iodine.
Thermal stability of the hydrides
How easily a hydrogen halide is broken up into its constituent elements when heated.
Hydrogen fluoride and chloride are very thermally stable and will not split into hydrogen and the halogen if heated under lab conditions.
Hydrogen bromide will split into hydrogen and bromine when heated.
Hydrogen iodide will split into hydrogen and iodine more easily then hydrogen bromide.
Thermal stability of the hydrides decrease down group 7. Further down the group covalent bonds are weaker so they can be broken more easily upon heating. Bonds are weaker down the group as halogen atoms get larger. Bonding pair gets further away from the nucleus so attraction gets weaker and bond is easier to break.
Chlorine in water purification
It’s used as it kills bacteria.
Chlorine reacts with the water in a disproportion reaction producing chloride and chlorate ions. This reaction produces HCl so an alkali is added.
Chlorate ions kills bacteria so treating water with chlorine makes it safe to drink or swim in.
Chlorine in water purification
It’s used as it kills bacteria.
Chlorine reacts with the water in a disproportion reaction producing chloride and chlorate ions. This reaction produces HCl so an alkali is added.
Chlorate ions kills bacteria so treating water with chlorine makes it safe to drink or swim in.
How can chlorine treat water?
By killing dangerous microorganisms
Prevents algae growth
Removes bad taste and smells
Removes discolouration
HOWEVER chlorine is toxic and can form potentially cancer causing compounds by reaction with organic matter in the water
How can chlorine treat water?
By killing dangerous microorganisms
Prevents algae growth
Removes bad taste and smells
Removes discolouration
HOWEVER chlorine is toxic and can form potentially cancer causing compounds by reaction with organic matter in the water
Effect of increasing heat on equilibrium
Will shift to favour the endothermic reaction because the excess heat needs to be removed from the system to lessen the effect of the initial increase. It will increase the yield of the products of the endothermic reaction.
Effect of increasing pressure on equilibrium
Favours the side of the reaction with fewer moles of gas as this helps to release the build up of pressure.
Effect of increasing concentration
Favours forward reaction as more molecules are available to react.
The equilibrium constant Kc
Indicates the position of the equilibrium for a reaction at a certain temp. Not affected by concentration or use of a catalyst but is by temperature. A large value of Kc suggests product formation is favourable and position of equilibrium will be far to the right. Small value says the opposite.
