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10.2 Standardize the given NaOH solution
volumetrically.

Date ________________

Volumetric analysis is used to find the concentrations of solutions by
means of a technique known as titration. In this technique a solution of unknown
concentration is combined slowly and carefully with a known volume of a
standard solution until a colour change shows the completion of the reaction.
The substance which indicates the completion of reaction by the change in its
colour is called an indicator. The moment at which the indicator changes colour
is called the end point. Either solution can be taken in a burette with the other
solution taken in a conical or a titration flask. With the help of this technique we
can check the purity of the products produced in industry or are available in the
market.

A large number of substances are available as acid base indicators, which
undergo a change in colour according to the pH of the solution (colour change
interval). The chief characteristic of these indicators is that the change in colour
is not sudden but takes place within a small interval of pH termed as the colour
change interval. For most acid base titrations we can, therefore, select an
indicator which shows a distinct colour change at a pH close to that which is
obtained at the end point.

Colour change and pH range of certain indicators

Indicator pH range/ Colour in acidic Colour in
colour change
interval solution alkaline solution

Phenolphthalein 8.3 – 10.0 Colourless Red or pink

Methyl Orange 3.1 -4.4 Red Pale yellow

Litmus 5.0-8.0 Red Blue

Bromothymol Blue 6.0 – 7.6 Yellow Blue

Titrand: The solution which is taken into the conical flask is called titrand or
titrate.

Titrant: The solution taken in the burette during titration is called titrant.

Concordant Readings: The burette readings which do not differ by more than
0.1 cm3.

Meniscus: The curved surface of a liquid in a narrow tube (e.g, burette or
pipette) is called meniscus. Note down the reading corresponding to the lower
level of the meniscus for the transparent liquids and the straight level for
coloured liquids.Avoid parallex error by noting down the reading at eye level.

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