PREPARATION OF STANDARD SODIUM CARBONATE SOLUTION AND STANDARDIZATION OF THE GIVEN ACID SOLUTION

 Principle:

One gram equivalent of Na₂CO₃ (53 g) dissolved in 1000 ml water gives 1N solution Na₂CO₃ is a weak alkali and used in standardization of acid solution. When a solution of a weak alkali is titrated against a strong acid, methyl orange indicator should be used.

            Na₂CO₃ + H₂SO₄                   Na₂SO₄ + H₂O + CO₂

Procedure:

A.  Preparation of standard Na₂CO₃ solution:

1.      Weigh by difference into a 250 ml beaker accurately about 1.325 g. of sodium carbonate using a weighing bottle.

2.      Add some distilled water into the beaker and dissolve the sodium carbonate with the help of glass rod.

3.      Transfer the solution into a clean 250 ml volumetric flask through a funnel.

4.      Wash the beaker 3 – 4 times with small amounts of distilled water and transfer the washings into the volumetric flask.

5.      Make up the volume with distilled water to the mark.

6.      Shake the solution thoroughly.

B.  Titration of given acid solution with standard Na₂CO₃ solution:

1.      Take clean burette and rinse it with the given sulphuric acid solution.

2.      Fill the burette with sulphuric acid solution and fix it in a burette stand.

3.      Pipette out 25 ml of the prepared sodium carbonate solution into a 250 ml Erlenmeyer flask.

4.      Add one drop of methyl orange indicator and mix the contents of the flask.

5.      Run down acid solution from the burette slowly and mix the contents of the flask.

6.      Note the volume of the acid required to change the colour of the solution into a permanent orange colour.

7.      Repeat the titration till at least two concordant readings are obtained.

Observation:

Weight of weighing bottle with sodium carbonate before transferring              =   a g.

Weight of weighing bottle with sodium carbonate after transferring    =   b g.

Weight of sodium carbonate transferred                                                     =   (a – b) g.

Normality of sodium carbonate solution

            (a – b)             1

N₂ =                 X

            1.325           10

Burette reading	Titration I	Titration II	Titration III
Final reading
Initial reading
Volume delivered in ml.

Normality of sodium carbonate solution = N₂

Volume of sodium carbonate solution     = V₂ (25 ml)

Volume of acid solution required            = V₁ ml

Normality of acid                                         = N₁ (to be calculated)

Calculation:

Volume of acid solution X normality of acid solution = Volume of alkali solution X normality of alkali

N₁ X V₁  =  N₂ X V₂

             N₂ X V₂

N₁ =                                         

                 V₁

                                           1000 X 0.1

1000 ml of 0.1 N acid =                  = x ml of given acid solution diluted to 1000ml                                                  N₂

Result: The strength of given sulphuric acid solution is _______

Note: To obtain anhydrous sodium carbonate, pure sodium carbonate in porcelain dish at 29°C for one hour. To ensure complete conversion of the sodium bicarbonate weight till a constant weight is obtained. Immediately transfer the dish containing sodium carbonate to a desiccator.