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chemistry igcse acapprinted 94 · PDF 94
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in a given volume. For example, a dilute solution of hydrochloric acid (HCl) is often more acidic
than a concentrated solution of ethanoic acid (CH₃COOH), because even in lower amounts, HCl
fully dissociates, whereas CH₃COOH does not.
Oxides
Definition of Oxides
Oxides are compounds consisting of oxygen atoms bonded with atoms of another element. Some
common oxides include calcium oxide (CaO), nitrogen dioxide (NO₂), phosphorus pentoxide
(P₂O₅), sulfur trioxide (SO₃), and water (H₂O). Oxides are generally classified according to their
acidic or basic nature.
Types of Oxides
Acidic Oxides
Acidic oxides are produced when non-metal elements react with oxygen. They generally react with
bases to form salt and water. When dissolved in water, acidic oxides create acidic solutions,
lowering the pH. Examples of acidic oxides include sulfur trioxide (SO₃), nitrogen dioxide (NO₂),
and phosphorus pentoxide (P₂O₅).
Example: Sulfur Trioxide (SO₃)
Reaction:
SO3(l)+H2O(l)→H2SO4(aq)
Basic Oxides
Basic oxides form when metals combine with oxygen, often producing a high pH solution when
dissolved in water. They react with acids to produce salt and water. Examples of basic oxides are
potassium oxide (K₂O) and magnesium oxide (MgO).
Example: Magnesium Oxide (MgO)
Reaction:
MgO(s)+2HCl(aq)→MgCl2(aq)+H2O(l)
Neutral Oxides
Neutral oxides neither react with acids nor bases and thus are classified as neutral. They do not
alter the pH of water significantly. Common examples of neutral oxides include nitrous oxide
(N₂O), nitric oxide (NO), and carbon monoxide (CO).
Example: Nitric Oxide (NO)
Reaction: