Give the oxidation number of antimony in the following:

Question

a) SbH₃

b) H₂SbO₄^-

c) SbCl₃

Answer 1

Oxidation Numbers are used to indicate the oxidation states of each element in a compound

There are some ALWAYS rules:

F, Cl, Br, I ..... these have oxidation number -1

O, S, Se ..... these have oxidation number -2

Li, Na, K, Rb, Cs ..... these have oxidation number +1

Be, Mg, Ca, Sr, Ba ..... these have oxidation number +2

Al ..... has oxidation number +3

H (in acids) ..... has oxidation number +1

H (in hydrides) ..... has oxidation number -1

These oxidation numbers are coincidentally the same as the ionic charges

Let's look at some examples:

H₂O (water)

H ... +1 -----> there are two

O ..... -2

notice that +1 with +1 with -2 adds up to 0 for a neutral compound

H₂O₂ (hydrogen peroxide)

H ..... +1 -----> there are two

here is where O does not follow the rule

in order for 2 H and 2 O to add up to 0 ..... O must have oxidation state -1

CO (carbon monoxide)

O ..... -2

so C has oxidation state +2

CO₂ (carbon dioxide)

O ..... -2 -----> there are two

so C has oxidation state +4

As for the antimony in your problem

SbH₃ ..... should be consider a hydride

H₂SbO₄^- ..... the H and O follow the rules AND

instead of adding up to 0, the whole thing is an anion that adds up to -1

SbCl₃ ..... the Cl follows the rule