Chapter 11: Acids and Bases
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Definition of Acid
An acid is a substance that produce

hydrogen ions when dissolved in water.
All acids contain hydrogen. But not all

substances with hydrogen contains
acids (Water).
The hydrogen ions produced are

responsible for the properties of an acid.
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Some common acids
Man-made:

 Hydrochloric Acid (HCl)
 Sulphuric Acid (H2SO4)
 Nitric Acid (HNO3)
Natural Acids:

 Ethanoic Acid (Found in vinegar)
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Properties of Acids
Acids have a sour taste

 Acids dissolve in water to form solutions
which conduct electricity.
 Acids turn blue litmus paper red.
 pH value < 7.
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Chemical Properties of
Acids
Acids react with reactive metals to form
1.
hydrogen and a salt.
 Formula: Metal + Acid  Salt + Hydrogen
 Reactive metals give out electrons easily to
form positive ions.
 Example: Magnesium Ribbon with Dilute
sulphuric acid. Equation:
 Mg (s) + (H2SO4) (aq)  MgSO4 (aq) + H2 (g)
Very important!
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Chemical Properties of
Acids
To test for hydrogen, place a lighted splint at

the test tube and a “pop sound” will be heard.
 Some acid and metal reactions which do not
give hydrogen:
 Unreactive metals (copper and silver)
 Concentrated nitric acid reacts with metals but it
does not give hydrogen (gives nitrogen dioxide)
 Lead does not react as a coating is formed once
lead is placed inside the acid.
Very important!
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Chemical Properties of
Acids
2. Acids react with carbonates to form a salt,
carbon dioxide and water.
 Equation: Acid + Carbonate  Salt +
Carbon Dioxide + Water
 Example: Sodium Carbonate + Dilute
hydrochloric acid  Sodium Chloride +
Water + Carbon Dioxide
 Bubble the gas through limewater to test
for carbon dioxide.
Very important!
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Chemical Properties of
Acids
Acids react with metal oxides and
3.
hydroxides (Insoluble bases) to form salt
and water.
 General Equations:
Metal Oxide + Acid  Salt and Water.
Metal Hydroxide + Acid  Salt and Water
Very important!
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Acids only react when placed into water.

This is because water can break apart
the acid into hydrogen ions and a salt.
 Therefore, an acid dissociate in water
to produce hydrogen ions which are
responsible for the acidic properties.
 Acids only show their properties when
dissolved in water.
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The hydrogen ions produced are not

hydrogen gas.
 They react with metals like magnesium
to produce hydrogen gas and
magnesium ions.
 A few drops of water is enough to allow
an acid to dissociate.
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Sulphuric Acid:

 Detergents
 Car Batteries
Ethanoic Acid:

 Vinegar to preserve food
 Adhesives (glue)
Hydrochloric acid

 Cleaning metals
 Leather processing
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A base is any metal oxide or hydroxide.

 A base is a substance that reacts with an
acid to give salt and water only.
 Acid + Base  Salt and Water
Similar to: Acid + Metal Oxide/Hydroxide
 Salt and Water.
 Ionic Equation for this is always standard:
OH- + H+  H2O (l)
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Sodium Oxide

 Zinc Oxide
 Copper (II) Oxide
 Magnesium Hydroxide
 Aluminum Hydroxide
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Bases
Soluble Insoluble
Metal
Alkalis Oxides and
Hydroxides
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Definition
An alkali is a base that is soluble in

water.
 Some examples include:
 Sodium Hydroxide
 Potassium Hydroxide
 Calcium Hydroxide
 Barium Hydroxide
 Aqueous Ammonia
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Properties of Alkalis
Alkalis have a bitter taste and soapy

feel.
 Alkalis turn red litmus paper blue.
 pH value > 7.
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Chemical Properties of
Alkalis
All alkalis produce hydroxide ions

when dissolved in water.
 Example: Sodium Hydroxide + Water 
Sodium Ion + Hydroxide ion.
Very important!
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Chemical Properties of
Alkalis
All alkalis react with acids to form salt and

water only.
 This is also known as neutralisation.
 The salt depends on the acid used.
 Sulphuric Acid  Sulphide
 Hydrochloric Acid  Chloride
The ionic equation for this is standardized.

 H+ (aq) + OH- (aq)  H2O (l).
Very important!
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Alkalis heated with ammonium salts

gives off ammonia gas.
 General Equation: Alkali + Ammonium
Salt  Ammonia + Water + Salt.
 Ammonia has a strong smell and turn
red litmus paper blue.
 Example: Calcium hydroxide +
Ammonium chloride  Calcium Chloride
+ Water + Ammonia.
Very important!
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Alkalis can react with the solution of 1 metal

salt to give metal hydroxide and another
metal salt.
 General Equation: Alkali + Salt (of metal A)
 Metal Hydroxide + Salt (of metal B)
 Example: Sodium Hydroxide + Iron (II)
Sulphate  Iron (II) Hydroxide + Sodium
Sulphate.
Very important!
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Ammonia Solution:

 Window cleaning solutions
Calcium Oxide:

 To make iron, concrete, cement
Magnesium Hydroxide:

 Toothpaste to neutralise acid o teeth
 In antacids to relieve indigestion.
Sodium Hydroxide:

 In making soaps and detergents.
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Concentration tells us how much of a

substance is dissolved in 1dm3 of a
solution.
 It can be changed by either adding more
solute or more solvent.
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Strength refers to how easily an acid or

alkali dissociates when dissolved in
water.
 A strong acid like hydrochloric acid
dissociates easily in water (almost 100%
of the acid dissociates)
 A weak acid like ethanoic acid does not
fully dissociate when dissolved in water.
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The strength of an acid cannot be

changed.
 No matter how concentrated ethanoic
acid is, it is still a weak acid.
 The strength of an acid of an alkali can
be shown using the pH scale.
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