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Amphoteric Oxides.

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#1
Nov5-05, 09:00 AM
P: 49
Hi all,
I was wondering if anyone could help me with classing the following oxides as AMPHOTERIC.
Ie) They act as both lewis acids and bases.
My text book does not have a very thorough description.
Here's the list, with the ones I already know.


Li_2O

BeO

CO_2 -Only a Lewis Acid

P_4O_6

Cl_2O

Al_2O_3 -Amphoteric

BeO

SnO_2 -Amphoteric

Br_2O_7

PbO_2 -Amphoteric




Cheers for any help,
It will be much appreciated.
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GCT
#2
Nov5-05, 11:49 AM
Sci Advisor
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P: 1,769
to get an idea, try drawing out the lewis structure
Cesium
#3
Nov5-05, 12:06 PM
P: 274
Basic: alkali metals, alkali earth metals (except Be), and Tl
Amphoteric: Be, Al, Ga, In, Ge, Sn, Pb, As, Sb, Bi
Acidic: chalcogens, halogens, B, C, Si, N, P
Transitional Metals depend on oxidation state.

Basic:
Li2O + H2O --> 2LiOH

Amphortetric:
BeO + 2H+ --> Be+2 + H2O
BeO + H2O + 2OH- --> [Be(OH)4]2-

Al2O3 + 6 H+ --> 2 Al3+ + 3 H2O
Al2O3 + 3 H2O + 2 OH- --> 2 [Al(OH)4-]

SnO2 + 4H+ --> Sn+4 + 2H2O
SnO2 + 2H2O + 2OH- --> [Sn(OH)6]2-

PbO(s) + 2H+ --> Pb+2 + H2O
PbO(s) + H2O + 2OH- --> [Pb(OH)4]2-

Acidic:
CO2 + H2O --> H2CO3
P4O6 + 6H2O --> 4H3PO4
ClO2 + 2H2O --> 2HOCl
Br2O7 + H2O --> 2HBrO4

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#4
Nov6-05, 05:45 AM
P: 49
Amphoteric Oxides.

Thanks for the help both of you.

So if I draw a Lewis-structure to discern if a compound is amphoteric, then how exactly do I know,

Is it that the molecule requires a non-bonding pair of electrons to be a Lewis-Acid, and that it also requires an completely empty orbital to accept a pair of electrons, hence also being a Lewis-Base?

I mean, is that what makes a compound amphoteric?

Cheers again.
GCT
#5
Nov6-05, 03:51 PM
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P: 1,769
metal oxides are usually basic oxides, while those oxides of non-metals are acidic oxides such as carbon dioxide. You should review the equations in your text between the reaction of these oxides with water, and even a reaction of an acidic oxide with that of an basic oxide and compare it with the reaction of a strong arrhenius acid/base neutralization. Water for instance is amphoteric in a sense since it can be protonated (as a lewis base) and has a slightly basic arrhenius proton.
Cesium
#6
Nov6-05, 04:58 PM
P: 274
Ya for example you can have a neutralization reaction between an acidic oxide and a basic oxide to produce a salt:

2MgO + SiO2 --> Mg2SiO4


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