I can classify oxides as acidic, including SO2 and CO2, or basic, including CuO and CaO, related to metallic and non-metallic character.
I can describe amphoteric oxides as oxides that react with acids and with bases to produce a salt and water.
I can classify Al2O3 and ZnO as amphoteric oxides.
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Proton Transfer
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What are oxides?
Oxides are compounds made from one or more atoms of oxygen combined with one other element.
Examples of oxides include: MgO, ZnO, K2O, CO2, SO2, H2O
Oxides can be classified based on their acid-base characteristics.
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Acid and basic oxides
have different properties and values of pH
the difference in their pH = whether they are bonded to a metal or to a non-metal element
The metallic character of the element influences the acidic or basic behaviour of the molecule.
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Acidic Oxides
formed when a non-metal element combines with oxygen
react with bases to form a salt and water
When dissolved in water, they produce an acidic solution with a low pH.
Common examples include CO2, SO2, NO2 and SiO2
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Basic Oxides
formed when a metal element combines with oxygen
react with acids to form a salt and water
When dissolved in water they produce a basic solution with a high pH.
Common examples include CuO and CaO
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07 April 2023
Classifying Oxides
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Neutral Oxides
Some oxides do not react with either acids or bases and thus are said to be neutral.
Examples include N2O, NO, and CO.
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Amphoteric oxides
a group of oxides that can behave as both acidic and basic, depending on whether the other reactant is an acid or a base
In both cases, salt and water are formed.
most common amphoteric oxides: zinc oxide, ZnO and aluminum oxide, Al2O3
The hydroxides of both of these elements also behave amphoterically.
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Example
Example of aluminium oxide behaving as a base:
Al2O3+ 6HCl → 2AlCl3 + 3H2O
Example of aluminium oxide behaving as an acid:
Al2O3 + 2NaOH → 2NaAlO2 + H2O
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Exemption to the Proton transfer concept
This acidic and basic behaviour of amphoteric oxides is not easily explained by donating or accepting protons. A separate theory called the Lewis acid-base theory can identify acids or bases in these situations.
