Determine the oxidation states of the elements in the...

Determine the oxidation states of the elements in the compounds listed. None of the oxygen-containing compounds are peroxides or superoxides. (a) $\mathrm{H}_{3} \mathrm{PO}_{4}$ (b) $\mathrm{Al}(\mathrm{OH})_{3}$ (c) $\mathrm{SeO}_{2}$ (d) $\mathrm{KNO}_{2}$ (e) $\operatorname{In}_{2} \mathrm{S}_{3}$ (f) $\mathrm{P}_{4} \mathrm{O}_{6}$

Determine the oxidation states of the elements in the compounds listed. None of the oxygen-containing
compounds are peroxides or superoxides.
(a) $\mathrm{H}_{3} \mathrm{PO}_{4}$
(b) $\mathrm{Al}(\mathrm{OH})_{3}$
(c) $\mathrm{SeO}_{2}$
(d) $\mathrm{KNO}_{2}$
(e) $\operatorname{In}_{2} \mathrm{S}_{3}$
(f) $\mathrm{P}_{4} \mathrm{O}_{6}$

Key Concepts

Rules for Assigning Oxidation Numbers

A set of systematic rules is used to assign oxidation numbers to elements in compounds. These include that elements in their natural state have an oxidation state of zero, hydrogen is typically +1 (with exceptions in hydrides), oxygen is generally -2 (except in peroxides and superoxides), and the total of the oxidation numbers in a neutral molecule must sum to zero (or equal the net charge in ions).

Charge Balance and Sum-of-Oxidation Numbers

In any compound, the sum of the oxidation states of all atoms must equal the overall charge of the compound. This principle is essential for determining unknown oxidation states by setting up an equation where the sum of the assigned oxidation numbers equals zero for neutral molecules or matches the ionic charge for charged species.

Oxidation States

Oxidation states, or oxidation numbers, are a formalism used to describe the degree of oxidation of an element in a chemical compound. They signify the hypothetical charge an atom would bear if the bonding were completely ionic, which is a useful bookkeeping tool in redox reactions and electron transfer processes.

Transcript

00:01 In this question, we're asked to list the oxidation state of each of the elements in all of these compounds.

00:08 Let's begin with a.

00:10 We have h3 -p -o -4.

00:12 We know that hydrogen in the first group gets an oxidation state of plus 1.

00:22 Oxygen always gets a state, always, except for a few exceptions, gets oxidated state of minus 2.

00:29 That means that if there are four oxygens, you have a minus 8.

00:34 If there are three hydrogens, you get a plus three.

00:37 So the difference between plus three and minus eight, to get this to be neutral, you must have a plus five for the phosphorus.

00:49 So plus three, plus five is positive eight, four times negative two is minus eight.

00:54 So that's neutral.

00:55 In b, we have aluminum hydroxide.

00:58 We have three hydrogens, three oxygens, and one aluminum.

01:02 Again, we know from our rules, hydrogen, always plus one, oxygen always minus two, and the total charge of this together is minus one.

01:16 Since there are three negative one charges, aluminum to balance it out must be plus three.

01:24 We have three positive charges here, six negative charges and three more positive charges.

01:29 That's balanced out.

01:31 And c, selenium dioxide.

01:34 Again, oxygen minus 2.

01:37 If there are two of them, that means this is minus 4.

01:40 To balance that out, selenium must be plus 4.

01:45 In d, we have potassium nitrite...

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