Acid-Base Titration - Notes

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					_______________________________________________________________________ Neutralisation



                                                                                You will be able to:
                     Acid-Base Titration
                                                                          Describe the titration process
                                                                          of acid-base.
                                                                          Determine the end point of
                                                                          titration during neutralisation.
Titration is a very useful laboratory technique in which one
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
                                                                                   Did you know?
used to detect the end of he titration when it changes colour.
                                                                                The juice of purple
The at which this happens is called the end point.                              cabbage can act as an
                                                                                acid-base indicator.
                                                                                Purple cabbage
The end point of neutralisation is achieved when all the OH-                    contains a chemical
ions combine with all the H+ ions in the solution to form water                 substance known as
                                                                                anthocyanin that
which is neutral.                                                               changes colour when
                                                                                the pH value of a
                                                                                solution changes. In an
Since both reactants (acid and alkalis) and the products formed                 acidic solution, the
                                                                                purple cabbage purple
(salt and water) are colourless, the end point of neutralisation                cabbage is red or
can be determined by three methods as follow:                                   purple in colour. In an
                                                                                alkaline solution, the
                                                                                colour is blue or green.
    1. The use of acid-base indicators such as methyl orange,                   Other natural indicators
                                                                                include carrot juice,
        phenolphthalein and litmus.                                             yellow ginger powder
                                                                                and extracts from
    2. Measurement of the pH values of the solution on the                      certain types of red or
        computer interface during titration.                                    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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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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                                     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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posted:11/29/2011
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