1. Chapter Three

2.  An acid is a substance that produces hydrogen
ions when dissolved in water.
 Examples of acids are hydrochloric acid (HCl),
sulphuric acid (H2SO4), nitric acid (HNO3) and
ethanoic acid (CH3COOH).
 Sulphuric acid is used in detergents, fertilisers and
car batteries.
 Ethanoic acid is used in vinegar and making
adhesives.
 Hydrochloric acid is used in leather processing and
cleaning materials.

3.  Acids have a sour taste.
 Acids dissolve in water to form solutions that
conducts electricity.
 Acids turn blue litmus red.
 Acids have pH value less than 7.
 Acids react with metals, carbonates and bases.

4. Metal reactions
 Acid + Reactive Metal Salt + Hydrogen
Carbonate reactions
 Acid + Carbonate Salt + Water + Carbon dioxide
Base reactions
 Acid + Base Salt + Water

5.  Test for Hydrogen
 Place a lighted splint at the mouth of a test tube.
 A pop sound is heard and the splint is extinguished.
Hydrogen is thus present.
 Test for Carbon dioxide
 Bubble the gas through limewater.
 If carbon dioxide is present, the limewater will turn
chalky and a white precipitate would be formed.

6.  An alkali is a metal oxide or hydroxide that is
soluble in water.
 Examples :
 sodium hydroxide (NaOH)
 potassium hydroxide (KOH)
 calcium hydroxide [Ca(OH)2]
 barium hydroxide [Ba(OH)2]
 aqueous ammonia (NH3).

7.  Ammonia solution
 Fertilisers
 Window cleaning solutions
 Calcium oxide
 To neutralise acidic soil
 Iron, concrete and cement
 Magnesium hydroxide
 Toothpaste to neutralise acid on teeth
 Antacids to relieve indigestion
 Sodium hydroxide
 Soaps and detergents
 Industrial-cleaning detergents

8.  Alkalis have a bitter taste and soapy feel.
 Alkalis dissolve in water to produce hydroxide
ions.
 Alkalis turn red litmus blue.
 Alkalis have pH value more than 7.
 Alkalis react with metals, ammonium salts and
acids

9. Metal reactions
 Alkali + Salt A Metal hydroxide + Salt B
Ammonium salt reactions
 Alkali + Ammonium Ammonia + Water + Salt
Base reactions
 Alkali + Acid Salt + Water

10. Taste Solubility
 Acids have a sour taste.
 Acids dissolve in water
to form solutions that
conducts electricity.
 Acids turn blue litmus
red.
 Acids have pH value less
than 7.
 Acids react with metals,
carbonates and bases.
 Alkalis have a bitter
taste and soapy feel.
 Alkalis dissolve in water
to produce hydroxide
ions.
 Alkalis turn red litmus
blue.
 Alkalis have pH value
more than 7.
 Alkalis react with
metals, ammonium salts
and acids.
Litmus pH value Reactions

11. Test for Ammonia
 Place a piece of moist red litmus paper in the
solution
 If ammonia is present, the moist red litmus paper
will turn blue.

12. Indicator Colour in Acids pH value Colour in Alkalis
Methyl orange Red 3 – 5 Yellow
Screened Methyl orange Violet 3 – 5 Green
Litmus paper Red 5 – 8 Blue
Bromothymol blue Yellow 6 – 8 Blue
Phenolphtalein Colourless 8 – 10 Pink
Red cabbage juice Pink Nil Green
Hydrangea flower Blue Nil Red

13.  When an acid and alkali react together, they
neutralise each other. Their properties are
removed.
 The pH value of the acid is increased while the pH
value of the alkali is decreased. The neutral
mixture has a pH value of 7.
 Water is formed together with a new substance
called a salt.

14.  A salt is a ionic compound formed when a metallic
or ammonium ion neutralises hydrogen ions of an
acid.
 Calcium chloride
 CaO + 2 HCl CaCl2 + H2O
 Zinc sulphate
 ZnO + H2SO4 ZnSO4 + H2O
 Sodium nitrate
 NaOH + HNO3 NaNO3 + H2O