Chapter 5 : Oxydation number

Question 1

Oxidation number

Answer 1

The charge the atom would have in a molecule (or an ionic compound) if e- were completely transfered.

Question 2

Oxidation

Answer 2

A species is oxidized when it loses one or more e-, and its calles a reducing agent.

Question 3

Reduction

Answer 3

a species is reduced when it gains 1 or more e-, and its called an oxidizing agent.

Question 4

Oxidation and reduction

Answer 4

always occur together, never in isolation. If something gains e-, something else had to loose them.

Question 5

free elements (uncombined state) have an oxidation number of 0

Answer 5

Na, Be, K, Pb, H2,O2,P4

Question 6

Monoatomic ion

Answer 6

The oxitation number is equal to the charge of the ion.

Li+=Li=+1, Fe3+=Fe=+3, O2-=O=-2

Question 7

Exception

Answer 7

H2O2=-1, O2=-1

Question 8

Oxidation of H

Answer 8

The oxidation of hydrogen is +1, except when its bonded to metals in binary compounds, called metal hybrides. In these cases, its oxidation number is -1 (NaH, CaH2).

Question 9

Group IA

Answer 9

+1

Question 10

Group IIA

Answer 10

+2

Question 11

Fluorine

Answer 11

-1

Question 12

When its equal to 0

Answer 12

The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to 0 or the charge of the ion.

Question 13

When oxidation ?

Answer 13

An atom is oxidised when its oxidation number increase.

Question 14

When reduced ?

Answer 14

An atom is reduced when its oxidation number decrease.