Preparation and standardization of 0.025 M Sulphuric acid BP Volumetric Solution
1. PREPARATION:
Carefully add 1.4 ml of Sulphuric acid to 50 ml of water and dilute to 1000 ml with the same solvent.
2. STANDARDISATION:
Dissolve 0.050 g of anhydrous Sodium carbonate in 50 ml of water, add 0.1 ml of Methyl orange solution and titrate with the Sulphuric acid solution until the solution begins to turn reddish yellow. Boil for about 2 minutes, cool and titrate again until the reddish yellow colour is restored.
Each ml of 0.025 M Sulphuric acid is equivalent to 2.65 mg of Na2CO3.
Calculation:
Molarity (M) = [0.025 x Weight of Na2CO3 (in g)]/[ Titration reading (in ml) x 0.00265]
Limit: 0.025 M ± 5 % (0.0238 M – 0.0263 M)
3. PREPARATION OF INDICATORS / REAGENTS:
a. Methyl orange solution:
Dissolve 0.1 g of Methyl orange in 80 ml of water and add sufficient Ethanol (96 %) to produce 100 ml.
Sensitivity: A mixture of 0.1 ml of the solution and 100 ml of carbon dioxide free water is yellow. Not more than 0.1 ml of 1 M Hydrochloric acid VS is required to change the colour of the solution to red.
Colour change: pH 3.0 (red) to 4.4 (yellow)
4. STORAGE CONDITION:
Store in glass-stoppered bottles.