electrolysis (summarised)

electrolytic cell definition

consists of two electrodes dipped into an electrolyte (one which conducts electricity in molten or aqueous state) and is chemically decomposed when an electric current passes through it

for electrolyte (must be molten or aqueous) but what if solid?

1. no electricity produced

2. does not contain mobile ions unlike molten or aqueous state so no reaction occurs

electrolytic cell process/reaction

• non spontaneous (needs a battery )

• electrical —> chemical energy

draw + explain set up

1. positive terminal of battery—> positive ions for that electrode (vice versa)

2. electrons move from anode to cathode via connecting wire

3. at anode , oxidation occurs / at cathode ,reduction occurs

4. anion in electrolyte moves to anode to undergo oxidation

5. cation in electrolyte moves to cathode to undergo reduction

polarity at anode and cathode for electrolysis

anode —> positive

cathode —> negative

(because of the terminal of the battery it Is connected to)

movement of ions in electrolyte

1. anion move towards anode

2. cation moves towards cathode

movement of electrons in the circuit

from anode to cathode through connecting wire ONLY

(because at anode oxidation occurs = lose electrons —> Zn—>Zn²⁺+2e^-) and cathode is where reduction occurs =gain electron from the ones anode has released —> Cu_²⁺ + 2e^- —>Cu
)

electrolysis of molten salt

presence of only liquid cation and anion in electrolyte

product at anode

gas from oxidation of anion

product at cathode

Liquid Metal from reduction of cation

inert (chemically inactive)electrodes for electrolysis

1. graphite (high melting point, react with oxygen)

2. platinum (low melting point , dont react with oxygen)

aluminium is extracted from

bauxite which contains aluminium oxide mixed with iron oxide (Fe₂O₃)and silica SiO₂

• electrolysis of molten aluminium oxide will yield aluminium

pure aluminimum oxide characteristics

1. expensive

2. dangerous to carry out

3. high melting point

pure aluminimum oxide is mixed with

cryolite (Na₃AlF₆), melts at lower temp

carbon anodes

• frequently attacked by oxygen gas at high temperature to form gaseous products, mainly carbon dioxide

• this causes carbon anodes to burn away so must be replaced regularly

more reactive metal

stronger reducing agent/gets oxidised

voltaic cell

serves like a battery + convert chemical energy to electrical energy

• electrical energy produced from spontaneous redox reaction in which electrons are transferred through an external circuit

simple voltaic cell consists of

• 2 electrodes made of metals with different reactivities

• both electrodes immersed in aqueous electrolyte solution

electrons flow form to __ (voltaic cell)

• through the external circuit (wire) to the less reactive metal which acts as the positive terminal (cathode)

• at the cathode , positive ions in the electrolyte gain electrons and are reduced to form neutral atoms Eg : Cu²⁺+2e^- —> Cu

the greater the distance between two elements

greater cell voltage

voltaic cell polarity of electrodes

cathode : postive

another : negative

(because of the flow of electrons)

observations in reactions

at the anode : electrode “dissolves” into solution / becomes smaller/eventually gone/mass decrease (ion discharged into electrolyte )

at the cathode : electrode gain mass / become larger in size (gain ion from electrolyte )

solution: talk about colour change

explanation for the diagram/why use hydrogen

• at cathode : attract positive cations (hydrogen is positive )

• then hydrogen is more reactive than copper , copper will be reduced until used up so left with hydrogen and forming bubbles/efferversence