C3.4 Electrolysis Flashcards
Electrolysis definition
An Electric current is used to breakdown an ionic substance
Electrolyte definition
The substance being broken down
What substances does electrolysis work on?
Only works on substances made up of ions - ionic compounds, these are mostly the compounds of metals and non-metals
When will Electrolysis work?
Will only work if the ions in the substance are free to move - will not work on solids but works on liquids, solutions and molten compounds
Cathode
Negatively charged electrode, positively charged ions will go here to gain electrons
Anode
Positively charged electrode, negatively charged ions will go here to lose electrons
Cation
Positive ion - metal
Anion
Negative ion - non-metal
What does electrolysis do?
Turns ions back into atoms or molecules
What electrode does oxidation occur?
Anode
What electrode does Reduction occur?
Cathode
What is a REDOX reaction?
a reduction-oxidation reaction, a chemical reaction where the oxidation number of an atom, molecule or ion changes by losing or gaining electrons
Test for Oxygen
Relights a glowing splint
Test for Hydrogen
‘Squeaky pop’ when lit
PANIC
Positive Anode Negative Is Cathode
Ionic half equations - sodium chloride
Sodium - Na+ + e- –> Na
Chloride - 2Cl- –> Cl2 + e-
OILRIG
Oxidation Is Loss Reduction Is Gain
LIPGIN
Loss Is Positive Gain Is Negative
REDCAT
REDuction CAThode
ANOX
ANode OXidation
What is Brine?
An Aqueous solution
What do water molecules break up into?
Hydrogen ions H+
Hydroxide ions OH-
cations - positive ions - discharge series
harder –> easier to be discharged
Na+, Mg2+, Al3+, H+, Cu2+
anions - negative ions - discharge series
harder –> easier to be discharged
SO42-, NO3, OH-,Cl-, Br-, I-
if the ion is a halogen will it be discharged over hydroxide ions?
yes - halogen is discharged at the anode
if the ion is not a halogen will it be discharged over hydroxide ions?
no, hydroxide ions from the water are discharged to make water and oxygen gas - other ions stay in solution
if + ions (metals) are more reactive than hydrogen what is produced?
Hydrogen
- metals more reactive than hydrogen - K, Na, Ca, Mg, Zn, Fe
if + ions (metals) are less reactive than hydrogen what is produced?
metal
- metals less reactive than hydrogen - Cu, Ag, Au
if - ions are not halogens what is produced?
oxygen
- negative ions that aren’t halogens - SO42-, NO3-, CO32-
what electrodes are normally used in electrolysis?
carbon - inert (non-reactive) - don’t take part in the reaction themselves
what happens at a copper anode?
- as the anode is not inert, it loses electron and copper ions go into solution - anode gets smaller
Cu (s) –> Cu2+ (aq) + 2e-
what happens at a copper cathode?
copper ions (rather than hydrogen ions) are discharged because they are lower in the discharge series Cu2+ (aq) + 2e- --> Cu (s)
describe the process of coper refining
- impure copper is used as anode - thin strip of copper used as cathode
- solution of copper sulphate is used as electrolyte
- a deposit of impurities from copper anode remain below anode (sludge)
what happens in electroplating?
metal ions formed at anode are transferred to cathode where they are deposited as metal - plating the object (spoon) as / at the cathode
uses for electroplating
- protect other more reactive metals from corrosion - e.g. steel coated in tin to protect it from air and water
- improve appearance of objects - e.g. jewellery
what are the most common plating metals used in electroplating?
- copper
- chromium
- nickel
- silver
- tin
what ore do you get aluminium oxide from?
bauxite
what is in bauxite?
the ore for aluminium oxide - has other metal oxides so have to separate before carrying out electrolysis of aluminium oxide
