[Gradient]

Hi. I am using a practice test to prepare for the CLEP chemistry exam, and I have trouble understanding why I answered some questions incorrectly.

I am given five options:

(A) Hydrofluoric acid
(B) Carbon dioxide
(C) Aluminum hydroxide
(D) Ammonia
(E) Hydrogen peroxide

I must pick exactly one option for each of these two predicates below. (The same choice may be used for both predicates.)

• Is a good oxidizing agent
• Has amphoteric properties

When taking this test, I answered "(E) Hydrogen peroxide" for both 1 and 2. My reasoning was that hydrogen peroxide is capable of gaining electrons, as in

H₂O₂ + 2e^- 2OH^-,

and it's capable of losing electrons, as in

H₂O₂ O₂ + 2H⁺ + 2e^-,

so it could function as both an oxidizing and a reducing agent. Because it can accept and donate electron pairs, it can qualify as both a Lewis acid and a Lewis base, and as such, it has amphoteric (acidic and basic) properties.

This reasoning is apparently incorrect: the correct answer for 1 is "(E) Hydrogen peroxide," but the correct answer for 2 is "(C) Aluminum hydroxide."

A quick search reveals to me that, yes, aluminum hydroxide does indeed have amphoteric properties. This is also supported by the compound's Wikipedia page. But what makes my line of reasoning incorrect? Why does hydrogen peroxide not have amphoteric properties? Furthermore, if aluminum hydroxide is amphoteric, does it not qualify as a Lewis acid (an electron acceptor) and therefore qualify as a "good oxidizing agent"?

On a more general note, I want to be able to tackle problems like this in the future. I want to be able to tell the difference between an oxidizing agent and a Lewis acid.

What distinguishes the term "Lewis acid" from the term "good oxidizing agent"? What distinguishes the term "Lewis base" from the term "good reducing agent"?

EDIT: I fixed a mistake with my chemical equation for hydrogen peroxide's loss of electrons.

[Borek]

I believe you use a rather strange definition of the amphoterism. But even if the definition involving Lewis acids/bases is right, aluminum hydroxide is a common example of the amphoteric substance, so there is no need to use some far fetched ideas. Stick to the KISS principle

[Babcock_Hall]

When a Lewis base "donates" electrons, it is really sharing them with the Lewis acid.  A reducing agent gives electrons to an oxidizing agent, but I would not say that the electrons are shared.  Does that help?