Exambusters Study Cards 17 Oxidation and Reduction


A solute whose aqueous solution contains ions and conducts electricity.

e.g. acids, bases, salts


A solute whose aquesous solution does not conduct electricity.

e.g. sugar, benzene, most organic compounds

A positively charged electrode which attracts anions; where oxidation takes place.
A negatively charged electrode which attracts cations; where reduction takes place.
The loss of electrons. Cumetal → Cu2+ + 2e
The gain of electrons. Zn2+ + 2e → Znmetal
Electrode Potential
A measure in volts of the tendency of atoms to gain or lose electrons. Relative to a hydrogen oxidation reaction which has an assigned value of zero.
Half Reaction
One of the two parts, either the reduction of the oxidation, of an oxidation-reduction (redox) reaction.
Write half reaction: oxidation of sodium metal
Na → Na+ + e
Write half reaction: reduction of sulfur atoms
S + 2e → S2-
How can you determine if a redox reaction will take place spontaneously?

Add the electrode potentials of the two half reactions.

If the result is positive, the reaction is spontaneous;

if negative, the reaction is not spontaneous.

Electrolytic Reaction
Redox reactions which do not occur spontaneously can be forced to take place by supplying an external current. e.g. electroplating, electrolysis
Electromotive Series
A chart listing the relative activities (oxidation potential) of metals.

A unit of electric charge which deposits by electrolysis one equivalent weight of an element;

one faraday = 96,500 coulombs.

Equivalent Weight
The number of grams of an element which will accept or donate one mole of electrons.
How many faradays are required to reduce 108 g of Ag ions to Ag metal from molten AgCl?
A faraday reduces one equivalent weight of substance. There are 108 g in one mole of Ag. The reaction requires one faraday.
Voltaic Cell

A battery.

Spontaneous redox reactions between chemical components create voltage.

e.g. in cars, lead storage battery;

flashlights, dry cell (AA, C, D, 9-volt etc.)

Oxidizing Agent
A substance which causes another substance to be oxidized; oxidizing agent is simultaneously reduced.
Reducing Agent
A substance which causes another substance to be reduced; reducing agent is simultaneously oxidized.