Amphoteric vs amphiprotic

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Amphoteric vs amphiprotic

Postby BriannaWillingham_1G » Sun Nov 22, 2015 8:51 pm

What is the difference between an amphoteric and an amphiprotic compound?
I understand that amphiprotic means that a compound can act as an acid or a base, whereas amphoteric means that a compound can react with an acid or base, but if a compound can react with an acid or base, doesn't that mean that it can be an acid or a base?
In other words, aren't amphiprotic and amphoteric the same thing?

Divya Prajapati 1E
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Re: Amphoteric vs amphiprotic

Postby Divya Prajapati 1E » Sun Nov 22, 2015 9:28 pm

Most of the time, you will be using the term amphoteric, as it does not require a substance to accept and donate protons. An amphiprotic substance, on the other hand, is specifically an amphoteric substance that transfers H+ ions.

I found the following explanation on this website:

An amphiprotic substance is one which can both donate hydrogen ions (protons) and also accept them. Water is a good example of such a compound. The water acts as both an acid (donating hydrogen ions) and as a base (by accepting them). The "protic" part of the word refers to the hydrogen ions (protons) either being donated or accepted. Other examples of amphiprotic compounds are amino acids, and ions like HSO4- (which can lose a hydrogen ion to form sulphate ions or accept one to form sulphuric acid).

But as well as being amphiprotic, these compounds are also amphoteric. Amphoteric means that they have reactions as both acids and bases. So what is the difference between the two terms?

All amphiprotic substances are also amphoteric - but the reverse isn't true. There are amphoteric substances which don't either donate or accept hydrogen ions when they act as acids or bases. There is a whole new definition of acid-base behaviour that you are just about to meet (the Lewis theory) which doesn't necessarily involve hydrogen ions at all.

A Lewis acid is an electron pair acceptor; a Lewis base is an electron pair donor (see below).

Some metal oxides (like aluminium oxide) are amphoteric - they react both as acids and bases. For example, they react as bases because the oxide ions accept hydrogen ions to make water. That's not a problem as far as the definition of amphiprotic is concerned - but the reaction as an acid is. The aluminium oxide doesn't contain any hydrogen ions to donate! But aluminium oxide reacts with bases like sodium hydroxide solution to form complex aluminate ions.

You can think of lone pairs on hydroxide ions as forming dative covalent (coordinate) bonds with empty orbitals in the aluminium ions. The aluminium ions are accepting lone pairs (acting as a Lewis acid). So aluminium oxide can act as both an acid and a base - and so is amphoteric. But it isn't amphiprotic because both of the acid reaction and the base reaction don't involve hydrogen ions."

Omar Habib 3L
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Re: Amphoteric vs amphiprotic

Postby Omar Habib 3L » Sun Nov 22, 2015 9:32 pm

When a compound is amphoteric, it means it has both basic and acidic character. Thus, when the compound reacts with an acid, it shows that it's basic. When it reacts with a base, it shows that it's acidic. When a compound is amphiprotic, it means it can act as a proton donor and as a proton acceptor. So in a sense, amphiprotic compounds are also amphoteric in most cases, since they act as both an acid and base by being able to donate and accept protons.

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Re: Amphoteric vs amphiprotic

Postby Maddy_Larson_2J » Mon Nov 21, 2016 1:09 pm

I was talking with some classmates and they said amphiprotic kind of relates to the Bronsted definition of acids and bases? How is this so? Thank you

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Re: Amphoteric vs amphiprotic

Postby Maddy_Larson_2J » Mon Nov 21, 2016 1:12 pm

I see how it relates since the Bronsted definition of an acid is that it can give off a proton, but essentially that's what it says an Amphoteric compound does too. So I guess my question is why would the amphiprotic compounds directly related to the Bronsted definition and not amphoteric? Sorry for the confusion and thank you for the help

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Re: Amphoteric vs amphiprotic

Postby Chem_Mod » Mon Nov 21, 2016 1:28 pm

Amphoteric is an general term for compounds that can act as an acid or a base. However, there are also compounds (like water) that gain or lose a proton to form an acid or base and this proton is where amphiprotic comes from. Therefore, amphiprotic is a more specific definition that only applies to protic compounds

Elizabeth Harty 1A
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Re: Amphoteric vs amphiprotic

Postby Elizabeth Harty 1A » Sat Dec 07, 2019 4:16 pm

How do you know if something is amphiprotic?

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