Acids and Bases
Both acids and bases are corrosive
Examples of everyday acids and bases
Acidic: citric acid, e.g. lemon juice, orange juice, apples, sour milk, vinegar,
fizzy drinks and tea.
Neutral: pure water
Basic: tooth paste, lime water, bread soda, toothpaste, window cleaner and
caustic soda.
Indicators
Indicators tell us whether a substance is acidic, basic or neutral, but most
indicators do not tell us how strong that acid or base is. Universal indicator is a
special indicator that has the ability to turn a full range of colours according to
the pH value of the substance. Litmus paper, phenolphthalein and bromothymol
blue are other examples of indicators.
Some indicators such as red cabbage water, red onion water and turmeric water can be
made at home.
The pH scale
Litmus tells us if a substance is acidic or
basic but not how acidic or basic the
substance actually is.
The pH scale allows to quantify (put a
number) on the acid or base.
The pH of a solution can be found using:
(i) A pH meter
(ii) Universal indicator solution
(iii) pH paper (paper soaked in universal indicator solution)
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The pH scale tells us how acidic or basic a solution is
pH greater than 7: the substance is alkaline
pH less than 7: the substance is acidic
pH 7: the substance is neutral
Universal Indicator pH Scale
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Common strong acids and bases
Acids
hydrochloric acid
sulfuric acid
Nitric Acid
Bases
sodium hydroxide
calcium hydroxide
calcium carbonate
HCl
H2SO4
HNO3
NaOH
Ca(OH)2
CaCO3
Alkalis are bases that are dissolved in water
Sodium hydroxide (caustic soda) is an example of an alkaline substance.
Neutralisation
The properties of an acid are counteracted or neutralised by a base; this
type of reaction is called a neutralisation reaction.
When an acid reacts with a base the hydrogen in the acid is replaced by a metal and a salt is formed
General formula to represent neutralisation reaction:
Acid
+
→
Base
Salt
Example 1
hydrochloric acid
HCL
+
+
sodium hydroxide
NaOH
→
sodium chloride
→
NaCl
Example 2
hydrochloric acid
2HCl
+
+
calcium carbonate
CaCO3
→
calcium chloride
→
CaCl2
3
+
+
+
Water
Water
+
H2O
CO2 + Water
+ CO2 + H2O
A. Reaction of Metal Oxides with Acids
 Salt + Water
Metal Oxide + Acid
For example,
Copper Oxide + Sulfuric Acid
Copper Sulfate + Water
B Reaction of Metal Carbonates with Acids
acid + metal carbonate → salt + carbon dioxide + water
A. Reaction of Metal hydroxide with Acids
Metal hydroxide + Acid

Salt + Water
For example,
The word equation for this reaction is:
hydrochloric acid + sodium hydroxide → sodium chloride + water
The chemical equation is:
HCl + NaOH → NaCl + H2O
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