2. ELECTROLYSIS

What is electrolysis?

breaking down an ionic compound into its elements using electricity

Where does electrolysis occur?

in an electrolytic cell

What part of the electrolytic cell is 1

anode

What part of the electrolytic cell is 2

cathode

What part of the electrolytic cell is 3

electrodes

What part of the electrolytic cell is 4

electrolyte

What is an anode?

positive electrode

What happens at the anode?

negative ions are attracted to the anode and lose electrons

What is a cathode?

negative electrode

What happens at the cathode?

positive ions are attacted to the cathode and gain electrons

What is special about electrodes?

they are inert (unreactive)

What is electrolyte?

molten ionic compounds or solutions that conduct electricity, so ions are able to move

What is oxidation?

loss of electrons

Where does oxidation occur?

at the anode

What is reduction?

gain of electrons

Where does reduction occur?

at the cathode

What is an easy way to remember oxidation and reduction?

OIL RIG = Oxidation is Loss, Reduction is Gain

What is an easy way to remember which ion goes to which electrode?

PANIC = Positive Anode, Negative Is Cathode

What happens in the electrolysis of molten compounds?

the metal will be produced at the cathode and the non-metal at the anode

What happens at the anode at the electrolysis of molten lead bromide?

• negative bromide ions are attracted to the anode and lose electrons forming bromine atoms

• two bromine atoms join to form bromine gas

What happens to the bromine ions in the electrolysis of molten lead bromide?

bromine ions are reduced

What is the equation for the electrolysis of molten lead bromide at the anode?

• 2Br^-_(l) → Br₂ (g) + 2e^-

• 2Br-_(l) - 2e^- → Br_2(g)

What happens at the cathode at the electrolysis of molten lead bromide?

Positive lead ions are attracted to the cathode and gain electrons forming lead

What happens to the lead ions in the electrolysis of molten lead bromide?

lead ions are oxidised

What is the equation for the electrolysis of molten lead bromide at the cathode?

Pb²⁺_(l) + 2c^- → Pb_(s)

When do metals have to be extracted from molten compounds?

when the metal is more reactive than carbon so can’t be reduced by it

What is a disadvantage of extracting metals from molten compounds?

expensive because a lot of energy is needed to melt compiunds and produce electricity

What is aluminium ore?

bauxite

What is the formula for bauxite?

Al₂O₃

What is aluminium oxide dissolved in?

cryolite because it lowers the boiling point of bauxite

What happens at the anode in the extraction of aluminium?

• O^2- ions are attracted to the anode and lose two electrons forming oxyggen atoms

• two oxygen atoms join to make oxygen case

What is the equation for the extraction of aluminium at the anode?

• 2O^-2_(l) → O2_(g) + 4e^-

• 2O^-2_(l) - 4e^- → O2_(g)

What causes the anodes to wear away during the extraction of aluminium at the anode?

oxygen produced her reacts with the graphite producing CO₂

What happens at the cathode in the extraction of aluminium?

Al³⁺ ions attracted to the cathode gain 3 electrons

What is the equation for the extraction of aluminium at the cathode?

Al³⁺ (l) + 3e^- → Al (l)

What ions are contained in solution?

H+, OH-

What does the ions discharged at each electrode depend on?

the reactivity of the elements involved

What happens in the Electrolysis of Aqueous Solutions at the cathode?

H₂ produced unless the metal is less reactive than hydrogen

What happens in the electrolysis of Aqueous Solutions at the anode?

O₂ produced unless solution contains halide ions

What happens in the electrolysis of lead sulphate solution at the cathode?

• Pb²⁺ and H+ both attracted to cathode

• H+ less active so hydrogen gas forms

What is the equation for the electrolysis of lead sulphate solution at the cathode?

2H+_(aq) + 2e- →H_2(g)

What happens in the electrolysis of lead sulphate solution at the anode?

OH- and SO₄^-2 both attracted to anode oxygen gas is formed (no halide ions present)

What is the equation for the electrolysis of lead sulphate solution at the anode?

• 4OH-_(aq) → O_2(g) + 2H₂O_(l) + 4e-

• 4OH-_(aq) - 4e- → O_2(g) + 2H₂O_(l)

What is brine?

concentrated sodium chloride solution

What happens in the electrolysis of brine at the cathode?

• H+ and Na+ are both attracted to the cathode

• H+ gains an electrons forming hydrogen atoms

• 2 hydrogen atoms bond to form hydrogen gas

What is the equation for the electrolysis of brine at the cathode?

2H+_(aq) + 2e^- → H_2(g)

What happens in the electrolysis of brine at the anode?

• OH- and Cl- are both attracted to the anode

• Cl- loses an electron to form chlorine atoms (oxidation

• Two chlorine atoms bond to form chlorine gas

What is the equation for the electrolysis of brine at the anode?

• 2Cl^-_(aq) - 2e^- → Cl_2(g)

• 2Cl^-_{(aq) →} Cl_{2(g) +} 2e^-

What happens to the remaining Na+ and OH- in brine after electrolysis?

they remain dissolved in solution and bond forming sodium hydroxide

What is H₂ used for?

• make HCl

• alternative fuel

What is Cl₂ used for?

• make bleach

• kill bacteria

What is NaOH used for?

• make bleach

• make paper