1Electrolysis
Splitting up of compounds using electricity
2What happens when an electric current passes through a molten or aqueous ionic compound?
The compound decomposes
(breaks down into ions)
3What type of compounds can undergo electrolysis?
Ionic compounds only
(not covalent)
4Why can covalent compounds not undergo electrolysis?
They cannot conduct electricity
Not formed from ions
5Electrode
Metal or graphite rod which an electric current flows through
6Electrolyte
Molten or dissolved (aqueous) ionic compound
Contains ions that are free to move
Can conduct electricity
7Anode
The positive electrode (attracts negative anions)
8Anion
Negatively charged ion
Attracted (moves) to the anode
9Cathode
The negative electrode (attracts positive cations)
10Cation
Positively charged ion
Attracted (moves) to the cathode
11Flow of electrons in electrolysis
From anode, through power supply, to cathode (not through electrolyte)
12What carries charge through the electrolyte?
The positive and negative ions
13Can solid ionic compounds undergo electrolysis? Why?
Solid ionic compounds have no free ions which can move and carry charge
So they cannot conduct electricity
Ionic compound must be liquid (molten) or dissolved
14What happens when a molten ionic compound is electrolysed? (Eg: Sodium Chloride - NaCl)
Ionic compound breaks down into positive metal cations (Na⁺) and negative non-metal anions (Cl⁻)
Cations are attracted to the cathode and gain electrons - Metal formed at cathode(Sodium - Na)
Anions are attracted to the anode and lose electrons - Non-metal gas formed at anode (Chlorine - Cl₂)
15What other compound is present in aqueous solutions?
Water - H₂O
16What other ions are present in aqueous solutions?
Cation: Hydrogen ion - H⁺
Anion: Hydroxide ion - OH⁻
17In a solution where do the H⁺and OH⁻come from?
From the water
18What are Halogens?
Elements in group 7
19What are Halide ions?
Ions of group 7 elements
20Electrolysis of aqueous solutions:
Which ions are attracted to the positive anode?
Negatively charged OH⁻ ions and non-metal ions
21Electrolysis of aqueous solutions:
Rule at the positive anode if Halide ions are present?
Halide ions discharged at anode
Halide ions lose electrons and form halogen gas
OH⁻ remains in solution
22Electrolysis of aqueous solutions:
Rule at the positive anode if no Halide ions present?
OH⁻ discharged at anode
OH⁻ loses electron and forms oxygen gas (O₂)
Non-metal ion remains in solution
23Which ions are less reactive than hydrogen?
Copper, Silver, Gold
(Cu, Ag, Au)
24Electrolysis of aqueous solutions:
Which ions are attracted to the negative cathode?
Positively charged H⁺ ions and metal ions
25Electrolysis of aqueous solutions:
Rule at the negative cathode if metal is less reactive than hydrogen
Metal ions discharged at cathode
Metal ions gain electrons and form metal
H⁺ remains in solution
26Electrolysis of aqueous solutions:
Rule at negative cathode if metal is more reactive than hydrogen
H⁺ ions discharged at cathode
H⁺ ions gain electron and form hydrogen gas
Metal ion remains in solution
27When watching electrolysis, what does it mean if you see bubbling around an electrode?
A gas is formed at the electrode
28Redox:
OILRIG
Oxidation is Loss, Reduction is Gain
(Of electrons)
29Redox:
Oxidation
When a substance loses electrons
30Redox:
Reduction
When a substance gains electrons
31Redox:
What happens at the anode?
Negatively charged ions lose electrons - they are oxidised
32Redox:
What happens at the cathode?
Positively charged ions gain electrons - they are reduced
33Redox:
Half equation showing reduction at cathode of metal ion with charge of +1 (Na⁺)
Na⁺ + e⁻ ⟶ Na
(Na⁺ ion gains one electron (reduction) to produce Na atom)
34Redox:
Half equation showing reduction at cathode of metal ion with charge of +2 (Cu²⁺)
Cu²⁺ + 2e⁻ ⟶ Cu
(Cu²⁺ ion gains two electrons (reduction) to produce Cu atom)
35Redox:
Half equation showing reduction at cathode of hydrogen ions (H⁺)
2H⁺ + 2e⁻ ⟶ H₂
(2 H⁺ ions gain one electron each (reduction) to produce H₂ gas molecule)
36Redox:
Half equation showing oxidation at anode of non-metal ion with charge of -1 (Cl⁻)
2Cl⁻ ⟶ Cl₂ + 2e⁻
(2 Cl⁻ ions lose one electron each (oxidation) to produce Cl₂ gas molecule)
37Redox:
Half equation showing oxidation at anode of water molecule (when OH⁻ discharged)
2H₂O ⟶ O₂ + 2H⁺ + 2e⁻