C3.4 - Electrolysis Flashcards
what is electrolysis the process of?
- breakdown of a liquid during the conduction of electricity
- process in which an electric current is passed through a compound, causing a chemical change
what is required for electrolysis to happen?
current to flow
what is the electrolyte?
ionic compounds that dissolve in water to make a solution that conducts electricity
why are electrolytes able to conduct electricity?
the ions are able to move around (when an ionic compound is dissolved)
where do positively charged ions move to when a voltage is applied?
cathode electrode
where do negatively charged ions move to when a voltage is applied?
anode electrode
what charge does the anode have?
A-NO (so opposite)
Positive
what charge does the cathode have?
negative
what happens when an ion touches an electrode?
electrons are transferred (producing elements/whole atoms)
what happens when voltage is applied across an electrolyte?
charged ions are attracted to the oppositely charged electrodes
what is convection?
the process in which ions in the electrolyte move to replace discharged ions
what do water molecules in solutions split up to form?
H+ ions (hydrogen)
OH- ions (hydroxide)
what does the product formed at the cathode depend on?
reactivity of the metal
what does the product formed at the anode depend on?
if halide ions are present
if halide ions are present at the anode what happens?
the halogen is produced
what happens if halide ions are absent at the anode?
oxygen is produced
what happens if the metal ion is more reactive than hydrogen at the cathode?
hydrogen is produced
what happens if the metal ion is less reactive than hydrogen at the cathode?
the respective metal is produced
does oxidisation or reduction happen at the anode?
oxidisation (ions lose electrons)
does oxidisation or reduction happen at the cathode?
reduction (ions gain electrons)
what are inert electrodes? N
electrodes that are not changed during electrolysis (copper/platinum/graphite)
USED AS ANODE/CATHODE
what happens during the electrolysis of water?
hydrogen ions are discharged at cathode, hydroxide ions are discharged at anode
what are the four metals less reactive than hydrogen?
copper, silver, gold, platinum
what kind of electrodes are used during electroplating?
non-inert (and so they change)
what electrode is the object your want to coat in electrolysis?
cathode
which electrode is the piece of the metal you want to coat the object with?
anode
Electrolysis definition
The decomposition (breakdown) of a compound using an electric current.
Electrolyte definition
A compound in its liquid state or in solution which contains mobile ions and conducts electricity
When ions become atoms or molecules at an electrode, you say that the ions have been __
Discharged
Electrolysis overall explanation
Overall, ions move to an oppositely charged electrode during electrolysis .
The concentration of ions close to each electrode goes down as ions gain or lose electrons to become atoms.
Other ions in the electrolyte can move to replace them by diffusion and convection.
This could not happen in ionic compounds in solid state, which is why ionic compounds in the solid state cannot conduct electricity.
Electrolysis of water - reduction of H+ half equation
4H+(Aq) + 4e- —> 2H2(g)
Electrolysis of water - oxidation of HO- half equation
4OH-(aq) —> 2H2O(l) + O2(g) + 4e-
Electrolysis of water - overall balanced equation
2H2O(l) → 2H2(g) + O2(g)
Role of electrolyte in electroplating
A solution contains ions of the coating metal
Electroplating - coating copper jewellery with silver.
Cathode?
Anode?
Electrolyte?
Cathode - piece of jewellery
Anode - piece of silver
Electrolyte - silver nitrate solution (as contains silver ions and all nitrate salts are soluble in water so you know that silver nitrate will dissolve)
How electroplating works?
Metal ions from electrolyte are discharged on surface of object (cathode).
These ions are replaced by metal ions leaving the surface of the anode.
Overall, metal leaves the anode and is deposited on the object until the anode is used up.
Half equations of electroplating with silver
Anode+cathode
Anode:
Ag(s) -> Ag+(aq) + e-
Cathode:
Ag+(aq) + e- -> Ag(s)
In electroplating of silver, where do silver ions and electrons move?
Silver ions move through the electrolyte and electrons move through the wires between two electrodes
Why is copper purified?
The conducting part of electrical cables are made from copper.
Copper obtained straight from copper ores must be purified so it can conduct electricity well enough to be useful.
SO Another use of electroplating is to purify copper on an industrial scale for use in electrical wiring
Purifying copper -
Cathode?
Anode?
Electrolyte?
the cathode is pure copper
the anode is impure copper, produced from copper ore
the electrolyte is copper(II) sulfate solution
Purification of copper description with half equations
When the dc power supply is turned on:
At the cathode, copper ions from the electrolyte gain electrons and become copper atoms:
Cu2+(aq) + 2e- → Cu(s)
At the anode, copper atoms lose electrons and become copper ions in the electrolyte:
Cu(s) → Cu2+(aq) + 2e-
Over time, the pure copper cathode increases in mass and the impure copper anode decreases in mass. Impurities collect underneath the anode.
Risks and precautions of electrolysis
Copper(II) sulfate solution. Harmful through skin contact and can cause serious eye irritation. Wear gloves, wear eye protection and rinse hands after contact
Chlorine gas. Toxic if inhaled. Make sure the lab is well ventilated and avoid inhaling the gas and do not run the experiment longer than is necessary to collect a sample
DC electricity supply. Electric shock. Make sure electrodes do not touch and make sure that electricity supply is switched off before handling apparatus
