10. Electromagnetism

Question 1

REDOX summary

Answer 1

REDOX are essential to life - concerned with transfer of electrons between atoms and molecules.

During oxidation - electrons are lost, with oxidised substance releasing energy.

During reduction - electrons are gained, with reduced substance gaining energy.

These reactions are parallel: when one molecule oxidised, another is reduced!

Coupled chemical reaction = oxidation reduction reaction (redox).

Question 2

Meaning of mnemonic:

LEO IS A GERC

Answer 2

LEO IS A GERC

• Lose Electrons Oxidation is Anode
• Gain Electrons Reduction at Cathode

Question 3

Galvanic cell structure

Answer 3

Question 4

Electron flow in galvanic cell

Answer 4

Electrons flow from:

• anode (= anodic compartment) where oxidation occurs (= oxidation half cell)

to

• cathode (= cathodic compartment) where reduction takes place (= reduction half-cell).

Question 5

Electrolytic cell structure

Answer 5

Question 6

Electrolysis

Answer 6

Electrolysis – electro = charge difference & lysis = separation of ionic bonds

Question 7

Electrolytic cell

Answer 7

Electrolytic - current is imposed on system to drive non-spontaneous redox reaction = requires energy = using battery

Question 8

Difference between galvanic and electrolytic cell

Answer 8

• In galvanic cells - spontaneous oxidation reaction takes place at cell’s anode creating source of electrons. For this reason, anode = considered negative electrode.
• In electrolytic cells - non-spontaneous reduction reaction takes place at cell’s cathode using external electrical energy as source of electrons such as a battery. For this reason, cathode = considered negative electrode.

Question 9

Reduction Potential E° & Unit

Answer 9

Reduction Potential E° – measure of tendency (potential) of chemical species to be reduced = potential to acquire electrons. Measured in Volts.

Reduction is gaining electrons

Question 10

Strong Reducing Agents

Answer 10

Reducing agent is reducing something so itself is oxidised so found on right side of table.

Strongest reducing agent has most negative reduction potential.

Question 11

Strong Oxidising Agents

Answer 11

Oxidising agents get reduced so found on left side of table.

Strongest oxidising agent has most positive reaction potential E°.

Question 12

Interpreting Half-Reaction Tables

Answer 12

What happens if Br² added to solution that contains Cl⁻ and I⁻ ions?

Reduction of Br² has E° that is lower than that of Cl₂ but higher than I₂.

Thus, it will oxidise I^‑ but not Cl^-

Question 13

Spontaneous vs non-spontaneous reaction

Answer 13

Most positive E value = most spontaneous

Most neg E value not spontaneous.

Question 14

Does stoichiometric factors count?

Answer 14

Stoichiometric factors are NOT USED if one is simply calculating E° of cell (because concentrations are, of course, standard at 1 M)

Question 15

Oxidation Number

Answer 15

Element reduced during reaction if its oxidation number decreased during this reaction.

Element oxidised during reaction if its oxidation number increased during this reaction.