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Preparation and Standardization of Various Molar and Normal Solutions

Preparation and standardization of Oxalic acid, sodium hydroxide, hydrochloric acid, sodium thiosulphate, sulphuric acid and potassium permanganate.

Sodium Hydroxide Solution Preparation

  • Take about 100ml of distilled water in a cleaned and dried 1000 ml volumetric flask.
  • Add about 4.2 gm of Sodium hydroxide with continues stirring.
  • Add more about 700ml of distilled water, mix and allow to cool to room temperature.
  • Make up the volume 1000 ml with distilled water. Mix solution thoroughly.
  • Keep the solution for at least an hour and then carry out the standardization.

Sodium Hydroxide Solution Standardization

  • Accurately weigh about 0.5 g of potassium biphthalate, previously crushed lightly and dried at 120° for 2 hours.
  • Dissolve in 75 ml of carbon dioxide free water.
  • Add 2 drops of phenolphthalein, and titrate with the sodium hydroxide solution to the production of a permanent pink color.
  • Each 20.42 mg of potassium biphthalate is equivalent to 1 ml of 0.1N sodium hydroxide.
Calculation

         Wt. in gm of potassium biphthalate
M= -----------------------------------------------------
             0.20423 x ml NaOH solution

Hydrochloric acid Solution Preparation

  • Take about 100 ml of water in a cleaned and dried 1000 ml volumetric flask.
  • Add about 8.5 ml of Conc. Hydrochloric acid with continuous stirring. 
  • Add more about 700 ml of water, mix and allow to cool to room temperature. 
  • Make up the volume 1000 ml with water. Mix solution thoroughly. 
  • Keep the solution for at least one hour and then carry out the standardization.

Hydrochloric acid Solution Standardization

  • Accurately weigh about 0.5 g of THAM (Tris (hydroxymethyl)-amino methane (tromethamine), previously dried at 105° for 3 hours and cooled in a desiccator, transfer to a conical flask.
  • Dissolve in 50 ml of distilled water.
  • Add 2 drops of Bromocresol Green indicator.
  • Titrate with 0.1M Hydrochloric acid to a pale yellow endpoint.
  • Each 121.14 mg of tromethamine is equivalent to 1 ml of 0.1M hydrochloric acid.
  • Calculate the molarity by the following formula:
           THAM in mg
M = ---------------------
        121.14 x HCl in ml

Sodium Thiosulphate Solution Preparation

  • Take about 100 ml of water in a cleaned and dried 1000 ml volumetric flask.
  • Add about 25 gm of Sodium Thiosulphate with continues stirring.
  • Add about 0.2 gm of Sodium Carbonate with continues stirring.
  • Add more about 700 ml of water, mix.
  • Make up the volume 1000 ml with water. Mix solution thoroughly.
  • Keep the solution for at least one hour and then carry out the standardization.

Sodium Thiosulphate Solution Standardization

  • Accurately weigh about 210 mg of primary standard Potassium Dichromate, previously pulverized and dried at 120°C for 4 hours.
  • Dissolve in 100 ml of distilled water in a glass-stoppered, 500 ml conical flask.
  • Swirl to dissolve the solid, remove the stopper, and quickly add 3 g of Potassium Iodide, 2 g of Sodium Bicarbonate, and 5 ml of hydrochloric acid.
  • Insert the stopper gently in the flask, swirl to mix, and allow to stand in the dark for exactly 10 minutes.
  • Rinse the stopper and the inner walls of the flask with distilled water, and titrate the liberated iodine with the Sodium Thiosulfate solution until the solution is yellowish green in color.
  • Add 3 ml of starch indicator solution, and continue the titration until the blue color is discharged.
  • Perform a blank determination.
  • Calculate the molarity by the following formula:

                K2Cr2O7 in mg
M = ------------------------------
          49.04 x Na2S2O3 in ml

Sulphuric Acid Solution Preparation

  • Add slowly, with stirring, 6 ml of Sulphuric acid to about 800 ml of purified water.
  • Makeup to 1000 ml with purified water.
  • Allow cooling at 25°C.

Sulphuric Acid Solution Standardization

  • Weigh accurately about 0.2 g of anhydrous Sodium Carbonate, previously heated at about 270°C for 1 hour.
  • Dissolve it in 100 ml of water and add 0.1 ml of methyl red solution.
  • Add the acid slowly from a burette, with constant stirring, until the solution becomes faintly pink.
  • Heat the solution to boiling, cool and continue the titration.
  • Heat again to boiling and titrate further as necessary until the faint pink color is no longer affected by continued boiling.
  • 1 ml of 0.1 M sulphuric acid is equivalent to 0.0098 g of Na2CO3.
  • Calculate the molarity of solution by the following formula:
             Na2CO3 in mg
M = -----------------------------
            H2SO4 in ml x 9.8

Potassium Permanganate Solution Preparation

  • Dissolve 3.2 g of potassium permanganate in 1000 ml of water.
  • Heat on a water-bath for 1 hour.
  • Allow to stand for 2 days and filter through glass wool.
  • Standardize the solution in the following manner.

Potassium Permanganate Solution Standardization

  • To 25.0 ml of the solution in a glass-stoppered flask add 2 g of potassium iodide, followed by 10 ml of 1 M sulphuric acid. 
  • Titrate the liberated iodine with 0.1 M sodium thiosulphate, using 3 ml of starch solution, added towards the end of the titration, as an indicator. 
  • Perform a blank determination and make the necessary correction.
  • Store protected from light.
  • 1 ml of 0.1 M sodium thiosulphate is equivalent to 0.003161 g of KMnO4.


Ceric Ammonium Sulphate Solution Preparation

  • Dissolve 65 g of ceric ammonium sulfate with the aid of gentle heat, in a mixture of 30 ml of sulphuric acid and 500 ml of water.
  • Cool, filter the solution, if turbid, and dilute to 1000 ml with water.
  • Standardize the solution in the following manner.

Ceric Ammonium Sulphate Solution Standardization

  • Weigh accurately about 0.2 g of arsenic trioxide, previously dried at 105° for 1 hour, and transferred to a 500 ml conical flask.
  • Wash down the inner walls of the flask with 25 ml of a 8.0 % w/v solution of sodium hydroxide, swirl to dissolve, add 100 ml of water and mix.
  • Add 30 ml of dilute sulphuric acid, 0.15 ml of osmic acid solution, 0.1 ml of ferroin sulfate solution.
  • Titrate with the ceric ammonium sulfate solution until the pink color is changed to a very pale blue, adding the titrant slowly towards the end-point.
  • 1 ml of 0.1 M ceric ammonium sulfate is equivalent to 0.004946 g of As2O3.
  • Calculate the molarity of the solution by the following formula:
                          As2O3 in mg
M = ------------------------------------------------------
      Ceric Ammonium Sulphate in ml x 4.946
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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