C6 Electrolysis Flashcards
(24 cards)
What does electrolysis mean?
Breaking down using electricity
An electric current breaks down an ionic compound
What is an electrolyte?
The compound broken down by electrolysis
What happens during electrolysis
Positively charged ions move to the cathode
Negative ions move to the anode
How you set up the electrical circuit for electrolysis?
Two electrodes are dipped in the electrolyte with a gap between
These act as conducting rods
One is connected to the positive terminal and is the anode
The other is connected to the negative terminal and is the cathode
Electrodes usually made of an un reactive substance (inert) eg graphite so electrodes do not react with the electrolyte or products
What happens when ions reach the electrodes
They lose their charge and become elements
As elements they may turn to gas or metal deposits
Depends on the compound and it maybe molten
Explain electrolysis of zinc chloride
Zinc chloride is molten because as solid it will not conduct electricity
Zinc forms and deposits form at cathode
Chlorine gas given off at anode
Beware chlorine is toxic - wear safety mask.
Zncl2 (l)->Zn(s/l)+cl2(g)
What alternative is there to using molten ionic compounds
Some ionic substances dissolve in water releasing their electrons
What also happens with ionic compounds dissolved in water
The water also forms ions
Only metals below hydrogen in reactivity series are deposited from aqueous solutions
Eg copper (II) bromide : Cu2+ ions go to cathode Br- ions go to anode
What happens with covalent compounds
Covalent compounds cannot usually be electrolysed unless they ionise in water
Acids in water contain H+ (aq) ions plus negatively charged aqueous ions
What is reduction and give 2 examples of half equations?
Reduction is the gain of electrons
Na+ + e- ->Na
Al3+ + 3e- -> Al
What is oxidation and give 2 examples of half equations?
Loss of electrons
2Cl- -> Cl2 + 2e-
2O2- -> O2 + 4e-
What are the uses of aluminium
Trains Planes Foil Cars Drink cans Window frames Bicycle frames Power cables
Why is aluminium extracted by electrolysis
Very reactive
More reactive than carbon so it can’t be displaced by it
What is aluminium extracted from
Aluminium oxide which is also called alumina which has been purified from bauxite
It is mixed with molten cryolite to lower its melting point
What happens in electrolysis and what is the equation
Aluminium oxide -> aluminium + oxygen
Aluminium forms at the cathode - Al3+ + 3e- -> Al - redcuction
Oxygen at the anode 2O2- -> O2 + 4e- oxidation
It is a continuous reaction
What happens with the anodes
Oxygen reacts with carbon to make carbon dioxide
So carbon anodes burn away and need replacing
In electrolysis of aqueous solutions what happens if the metal is more reactive than hydrogen
Electrolysis will produce hydrogen not the metal eg Potassium chloride produces hydrogen Sodium bromide produces hydrogen Zinc chloride produces hydrogen But Copper sulphate produce copper Silver nitrate produces silver
What is produced along in electrolysis of aqueous solutions ?
And why?
Ions that make the ionic compound
H+ (hydrogen) ions
OH- (hydroxide) ions
Due to partial ionisation of water
What is a halogen
Flourine, chlorine, iodine, bromine, astatine
Reactive non metallic elements
Form strongly acidic compounds with hydrogen from which simple salts are made
If a halogen is present what happens
The halogen will be produced at the anode
Eg potassium chloride produces chlorine
Eg sodium bromide produces bromine
If no halogen is present what happens
Oxygen is formed
Eg copper sulphate produces oxygen at the anode
Eg silver nitrate produces oxygen
What is chlorine used for
To kill bacteria in swimming pools
Why must ionic compounds be molten or dissolved for electrolysis
They must be must molten so electrons are free and ions can move and carry charge
What happens at the electrodes?
Ions are discharged
They gain or lose electrons so have no charge
