Electron Transfer & Redox
What does oxidation mean in terms of electrons?
Loss of electrons
What does OIL RIG stand for?
Oxidation Is Loss, Reduction Is Gain
In a galvanic cell, where does oxidation occur?
At the anode
What is the SI unit for cell potential?
Volt (V)
What formula is used to calculate electrical charge?
q = lt
In the reaction
Cu(s) + 2Ag⁺(aq) → 2Ag(s) + Cu²⁺(aq)
which substance is oxidized?
Copper is oxidized because it loses electrons
Place the following entities in order of increasing strength as reducing agents (at SATP):
Cu⁺(aq), I₂(s), H₂O(l), F₂(g)
Increasing strength as reducing agents:
F₂(g) < H₂O(l) < I₂(s) < Cu⁺(aq)
What is the purpose of a salt bridge?
It maintains electrical neutrality and prevents charge buildup
What is the standard reduction potential of the hydrogen half-cell?
0.00 V
What is Faraday’s constant?
9.65 × 10⁴ C/mol e⁻
Define an oxidizing agent
A substance that gains electrons and is reduced
Which reaction is spontaneous?
A) Ag⁺(aq) + Mg(s)
B) Mg²⁺(aq) + Ag(s)
A is spontaneous
In a Zn/Cu galvanic cell, which direction do electrons flow?
From zinc to copper
Calculate the standard cell potential for a Zn/Cu cell
E°Cu²⁺/Cu = +0.34 V
E°Zn²⁺/Zn = −0.76 V
ΔE°cell = E°cathode − E°anode
ΔE°cell = 0.34 − (−0.76)
ΔE°cell = +1.10 V
Calculate the charge transferred by a 5.0 A current flowing for 2.0 hours
2.0 h × 3600 = 7200 s
q = It
q = (5.0)(7200)
q = 36 000 C
In the formation of water
2H₂ + O₂ → 2H₂O
which element is reduced?
Oxygen is reduced because its oxidation number decreases from 0 to −2.
Balance the following reaction occurring in acidic conditions:
Cr₂O₇²⁻(aq) + Cl⁻(aq) → Cr³⁺(aq) + Cl₂(aq)
Cr₂O₇²⁻(aq) + 14H⁺(aq) + 6Cl⁻(aq) → 2Cr³⁺(aq) + 3Cl₂(aq) + 7H₂O(l)
Write the net ionic equation for the galvanic cell with the line notation
Mg(s) | Mg²⁺(aq) || Cu⁺(aq) | Cu(s)
Mg(s) + 2Cu⁺(aq) --> Mg²⁺(aq) + 2Cu(s)
What does a positive value of ΔE°cell indicate?
The reaction is spontaneous
Why does salt speed up rusting?
Salt increases conductivity, allowing electrochemical reactions to occur faster
Write the balanced oxidation and reduction half reaction for
Br₂(l) + 2 NaI(aq) → I₂(s) + 2 NaBr(aq)
Oxidation:
2 I⁻(aq) → I₂(s) + 2 e⁻
Reduction:
Br₂(l) + 2 e⁻ → 2 Br⁻(aq)
Balance the following reaction occurring in basic conditions.
Pb(OH)₄²⁻(aq) + ClO⁻(aq) → PbO₂(s) + Cl⁻(aq)
Pb(OH)₄²⁻(aq) + ClO⁻(aq) → PbO₂(s) + Cl⁻(aq) + H₂O(l) + 2OH⁻(aq)
A functioning galvanic cell is produced using a silver electrode in a silver nitrate solution and a copper electrode in a copper(II) nitrate solution.
(a) Sketch the galvanic cell, labelling all parts.
(b) Write the two half-reactions.
(c) Write the net ionic equation.
(d) Describe the cell using line notation.
(a) Sketch / description of the galvanic cell:
Copper electrode in Cu(NO₃)₂(aq) solution = anode
Silver electrode in AgNO₃(aq) solution = cathode
Salt bridge (KNO3) connects the two solutions
Electrons flow from Cu to Ag through the wire
(b) Half-reactions:
Oxidation (anode):
Cu(s) → Cu²⁺(aq) + 2 e⁻
Reduction (cathode):
2 Ag⁺(aq) + 2 e⁻ → 2 Ag(s)
(c) Net ionic equation:
Cu(s) + 2 Ag⁺(aq) → Cu²⁺(aq) + 2 Ag(s)
(d) Line notation:
Cu(s) | Cu²⁺(aq) || Ag⁺(aq) | Ag(s)
State two differences between primary and secondary cells.
Primary cells are non-rechargeable
• Secondary cells are rechargeable
• Secondary cells regenerate reactants using external energy
Explain why zinc protects iron in galvanizing even if the coating is scratched
Zinc is more easily oxidized than iron, so zinc acts as a sacrificial metal and corrodes instead of the iron