_______________________________________________________________________Neutralisation You Will Learn to:
Acid-Base Titration
Describe the titration process
of acid-base. Titration is a very useful laboratory technique in which one
Determine the end point of
titration during neutralisation.
solution is used to analyse another solution. In acid-base
titration, a titrant (known concentration solution) is carefully
delivered from a burette to completely neutralise a known
volume of titree in a conical flask. An acid-base indicator is
used to detect the end of he titration when it changes colour.
The at which this happens is called the end point.
The end point of neutralisation is achieved when all the OHions combine with all the H+ ions in the solution to form water
which is neutral.
Since both reactants (acid and alkalis) and the products formed
(salt and water) are colourless, the end point of neutralisation
can be determined by three methods as follow:
1. The use of acid-base indicators such as methyl orange,
phenolphthalein and litmus.
2. Measurement of the pH values of the solution on the
computer interface during titration.
Did you know?
The juice of purple
cabbage can act as an
acid-base indicator.
Purple cabbage
contains a chemical
substance known as
anthocyanin that
changes colour when
the pH value of a
solution changes. In an
acidic solution, the
purple cabbage purple
cabbage is red or
purple in colour. In an
alkaline solution, the
colour is blue or green.
Other natural indicators
include carrot juice,
yellow ginger powder
and extracts from
certain types of red or
yellow hibiscus flower.
3. Measurement of the electrical conductivity of the
solution during titration.
Indicator
Colour in alkalis
Colour in neutral solution
Colour in acids
Methyl orange
Yellow
Orange
Red
Phenolphthalein
Light Pink
Colourless
Colourless
Litmus
Blue
Orange
Red
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_______________________________________________________________________Neutralisation Procedure of Acid-Base Titration
Procedure
1) Transfer 25 cm3 of sodium hydroxide, NaOH, into a
conical flask by using pipette.
2) Put a few drops of phenolphthalein into the sodium
hydroxide, NaOH solution.
3) Clamp the burette vertically on the retort stand and
fill in with 1 mol dm-3 hydrochloric acid, HCl.
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_______________________________________________________________________Neutralisation 4) Place the conical flask containing sodium hydroxide
solution on top of the white tile at the base of the
retort stand.
5) Record the initial volume of the hydrochloric acid in
the burette.
6) Add the hydrochloric acid into the conical flaks
slowly until the pink solution changes to colourless
while continuously shaking the conical flask.
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_______________________________________________________________________Neutralisation 7) Record the final volume of the hydrochloric acid on
the burette.
8) Repeat the titration process three times to obtain
more accurate volume of hydrochloric acid at the end
point.
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