electochemistry

Electrolysis

The breaking up of a substance due to the passage of electric current through it in aqueous solution or when molten

Electrolyte

A substance that conducts electricity when dissolved in water or when molten

Electrode

,Akers electrical contact with the electrolyte

Active electrode

Reacts with the electrolyte

Anagram

CNR APO

what is equation at anode for KI

2I- → I2 + 2e-

What is equation at cathode for KI

2H2O + 2e- → H2 + 2OH-

What colour is at anode for KI

Yellowish brown

What colour is at cathode for KI

Pink as OH- (base)

What electrode is used for KI

Platinum (inert)

K+ ions don’t gain electrons because they are

Very stable, more energy to be reduced

Acidified water anode

2H2O → 4H+ + O2 + 4e-

Oxygen produced

Acidified water cathode

2H+ + 2e- → H2

Hydrogen produced

What is observed in the acidified water experiment

Twice as much hydrogen as oxygen 2:1

Sodium sulfate anode

2H2O → O2 + 4H+ + 4e-

Acidic = red

In sodium sulfate, SO4- and Na+ too stable so

Water is oxidised and reduced

Sodium sulfate cathode

2H2O + 2e- → H2 +2OH-

Basic = blue

Copper sulfate electrode

Copper (active)

Copper anode

Cu → Cu2+ + 2e-

Copper removed from electrode

Copper cathode

Cu2+ + 2e- → Cu(down)

Copper deposited on electrode

electrochemical series

metals are arranged in order of their tendency to be oxidised

metals above x in the electrochemical series react with acids to produce hydrogen gas

hydrogen

when a metal from the electrochemical series is mixed with the ions of a metal lower down

the atoms of the more reactive push their electrons on to the ions of the less reactive

→ more reactive is oxidised

displacement of metals

if magnesium is dipped in copper sulfate, it becomes covered in x

and the blue solution becomes x

the reduced copper becomes displaced from CuSO4

copper

paler

application of displacement reactions

• use of scrap iron to extract copper (from CuSO4)

• chrome and nickel plating in cutlery

inert electrodes

graphite and platinum

active electrodes

copper and iron

Cr2O72- colour

yellow

Cu2+ colour

blue

what colour is the copper (II) chromate solution? why is urea added? what is the function of the hydrochloric acid?

olive green, to increase solution density, to complete the circuit

electrolysis is carried out in a

hoffman voltameter

sulfuric acid is added to water to help it

conduct electricity

Application of electrolysis - Electroplating

• a layer of metal is put onto surface of another metal

• nickel cutlery can be coated with silver, for value + appearance