This slide show covers the use of indicators and chemical reactions of acids and alkalies with reference to Cambridge IGCSE chemistry curriculum

1. Presented by: Mrs. Saima

2. Review:ACIDS/BASES/INDICATORS
 When an acid is dissolved in water we get an acidic
solution. When a base dissolves in water it is an alkali
and makes an alkaline solution. If a solution is
neither acidic nor alkaline it is neutral. Pure water is
neutral, and so is paraffin.
 Indicators are substances that change colour when
they are added to acidic or alkaline solutions. Litmus,
phenolphthalein, and methyl orange are all indicators
that are commonly used in the laboratory.

3. EFFECT ON LITMUS

4.  Different indicators
have different colours
in acidic, alkaline and
neutral solution.
 Focus on colours for
universal indictor,
phenolphthalein and
methyl orange.

5. OBJECTIVES
 Describe the characteristic properties of acids (as
reactions with metals, bases, carbonates and effect on
litmus and methyl orange)
 Describe the characteristic properties of bases (as
reactions with acids and with ammonium salts and
effect on litmus and methyl orange)

6. REVIEW: WHAT ARE ACIDS AND
BASES
 ACIDS are substances that form hydrogen ions (H+
(aq)) when
dissolved in water eg
 Hydrochloric acid HCl gives H+
(aq) and Cl-
(aq) ions,
 Sulphuric acid H2SO4 gives 2H+
(aq) and SO4
2- ions
 Nitric acid HNO3 gives H+
(aq) and NO3
-
(aq) ions.
 BASES are oxides and hydroxides of metals that react and
neutralise acids to form salts and water only. Bases which are
soluble in water are called alkalis. Not all bases fit into these
categories e.g. ammonia.
 Alkalis are substances that form hydroxide ions OH-
(aq) in water
eg
 Sodium Hydroxide NaOH gives Na+
(aq) and OH-
(aq) ions,
 Calcium Hydroxide Ca(OH)2 gives Ca2+
(aq) and 2OH-
(aq) ions.

7. REACTIONS OF ACIDS
 WITH METALS:
Acids react with metals to give hydrogen gas and salt. For
example;
zinc + hydrochloric acid  hydrogen + zinc chloride
Zn + HCl  H₂ + ZnCl ₂

8. REACTIONS OF ACIDS
 REACTION WITH METAL CARBONATES AND
HYDROGEN CARBONATES;
Acids react with carbonates and hydrogen carbonates to
produce carbon dioxide, salt and water
sodium carbonate + nitric acid  carbon dioxide + sodium nitrate + water
Na₂CO ₃ + HNO ₃  CO ₂ + NaNO ₃ + H ₂O

9. REACTIONS OF ACIDS
 REACTIONS WITH METAL OXIDES AND
HYDROXIDE /BASES : (NEUTRALISATION)
Acid react with metal oxides and hydroxide to produce
salt and water. This reaction is called neutralisation.
Metal oxides and hydroxide belong to a group of
compounds called BASES. They are chemical
opposites of acid and neutralise an acid.
HCl + NaOH  NaCl + H ₂ O

10. REACTIONS OF BASES
 NEUTRALISATION:
( PREVOIUS SLIDE)
 REACTION WITH AMMONIUM SALTS;
 Bases react with ammonium salts to give off
ammonia gas, salt and water.
ammonium chloride + sodium hydroxide → sodium chloride + ammonia + water
Other ammonium salts react with other
bases in the same way.

11. NEUTRALISATION
 Neutralisation is the reaction of an acid and base to give salt and water.
HCl + NaOH  NaCl + H ₂ O
 When the H+ ions from an acid react with the OH- ions from an alkali, a
neutralisation reaction occurs to form water. This is the equation for the
reaction:
 H+(aq) + OH-(aq) → H2O(l)
 For example, hydrochloric acid and sodium hydroxide solution react
together to form water and sodium chloride solution. The acid contains
H+ ions and Cl– ions, and the alkali contains Na+ ions and OH– ions. The
H+ ions and OH– ions produce the water, and the Na+ ions and Cl– ions
produce the sodium chloride, NaCl(aq).
 Because neutralisation reactions involve the loss and gain of hydrogen
ions(proton), this process is sometimes referred to as ‘proton transfer’.

12. REVIEW
 What is an acid?
 What is a base?
 What is the difference between a base and alkali?
 What do you mean by a strong or weak acid?
Give an example of each
 How do acids react with a metals? Write a word equation .
 Write down the reaction of sulfuric acid with calcium
carbonate.
 Explain the reaction of ammonium salts with bases.
 What is neutralisation. Give an example.