What are the oxidation numbers of...?

Question

What are the oxidation numbers of P and H in PH₄⁺?



A. P = +3 and H = –1

B. P = –3 and H = +1

C. P = –2 and H = +1

D. P = –1 and H = +1

E. P = +1 and H = –1

Answer 1

When you assign oxidation numbers for compounds that include Hydrogen, Hydrogen will be a +1 with nonmetals and a -1 with metals. Because Hydrogen is in a compound with P, which is a nonmetal, Hydrogen will have an oxidation number of +1.

The way I teach this is that I tell students to break up the entire molecule like this and place the oxidation numbers under each atom.

H H H H H P

+1 +1 +1 +1 +1 X

All of the numbers need to add up to the charge of the compound, which in this case is +1.

+1 +1 +1 +1 +1 X = +1

Solving this would give us X = -3

Therefore, P = -3 and H = +1