Electrochemistry

Question 1

Define redox processes.

Answer 1

Electrons are transferred when oxidation and reduction occurs.

Question 2

Define oxidising agent.

Answer 2

The substance that is being reduced, oxidises the other substance

Question 3

Define reducing agent.

Answer 3

The substance that is being oxidised, reduces the other substance

Question 4

Describe the oxidation numbers of uncombined elements, ions, groups 1,2,3, Hydrogen, Chlorine, Fluorine and Oxygen.

Answer 4

Uncombined elements: Always zero.
Ions: Oxidation number is the same as the charge on the ion.
Group 1,2,3: Always +1, +2, and +3 respectively
Hydrogen: +1 (except for hydrides where it is -1)
Chlorine: -1 (except if in a compound with F and O)
Fluorine: Always -1.
Oxygen: -2 (except it is -1 in peroxide and +2 in OF2)

Question 5

What are the rules for oxidation numbers?

Answer 5

Some elements can have varying oxidation numbers. These elements are:
- Nitrogen
- Sulfur
- Phosphorous
- Chlorine
- Oxygen (in the case of H2O2)
- Hydrogen (+1 if bonded to non-metal and -1 if bonded to metals)
- All transition metals

Question 6

Define disproportionation reaction.

Answer 6

When an element gets both oxidised and reduced in a reaction.

Question 7

Describe ionic half-equations.

Answer 7

Show oxidation and reduction stages in 2 equations.

Steps to writing a half-equation:
- Write down the species before and after the reaction
- Balance any atoms apart from oxygen and hydrogen
- Balance any oxygens with H2O
- Balance any hydrogens with H+ ions
- Balance charges with electrons (e-)