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Homework Help: Amphoteric Oxides.

  1. Nov 5, 2005 #1
    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.



    CO_2 -Only a Lewis Acid



    Al_2O_3 -Amphoteric


    SnO_2 -Amphoteric


    PbO_2 -Amphoteric

    Cheers for any help,
    It will be much appreciated.
    Last edited: Nov 5, 2005
  2. jcsd
  3. Nov 5, 2005 #2


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    to get an idea, try drawing out the lewis structure
  4. Nov 5, 2005 #3
    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.

    Li2O + H2O --> 2LiOH

    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-

    CO2 + H2O --> H2CO3
    P4O6 + 6H2O --> 4H3PO4
    ClO2 + 2H2O --> 2HOCl
    Br2O7 + H2O --> 2HBrO4
  5. Nov 6, 2005 #4
    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.
  6. Nov 6, 2005 #5


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    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.
  7. Nov 6, 2005 #6
    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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