Preparation and standardization of 0.5 M Hydrochloric acid BP Volumetric Solution
1. PREPARATION:
Dilute 42.5 ml of Hydrochloric acid with sufficient water to produce 1000 ml.
2. STANDARDISATION:
Accurately weigh and dissolve 0.5 g of Anhydrous Sodium carbonate in 20 ml of water, add 0.1 ml of Methyl orange solution and titrate with the Hydrochloric acid until the solution becomes reddish yellow. Boil for 2 minutes and continue the titration until the reddish yellow colour is restored.
Each ml of 0.5 M Hydrochloric acid VS is equivalent to 26.5 mg of Na2CO3
Calculation:
Molarity (M) = [0.5 x weight of Na2CO3 (in g)]/ [Titration reading (in ml) x 0.0265]
Limit: 0.5 M ± 5 % (0.4750 M – 0.5250 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.