PRACTICAL PHARMACEUTICAL ANALYSIS – PREPARATION AND STANDARDIZATION OF 1 N SODIUM HYDROXIDE

Object – Preparation & standardization of Sodium hydroxide (1 N solution)

Reference – 1. Siddiqui A.A. & Ali M., Practical Pharmaceutical Chemistry, CBS publishers and distributors, New Delhi, I edition, 1997, 6-7

  1. Rao G.D., Practical pharmaceutical analysis, Birla publishers Pvt. Ltd., Delhi, II edition, 2007-08, 25-26

Glasswares & apparatus required – digital balance, volumetric flask, pipette, conical flask, burette, burette stand

Chemicals required – sodium hydroxide pellets, distill water, phenolphthalein solution, hydrochloric acid, methyl orange solution.

Theory – A neutralization reaction involves the titration of the free bases with a standard acid (acidimetry), and the titration of free acid with a base (alkalimetry). These reactions include the combination of hydrogen and hydroxide ion to form water. The point at which this is reached is the equivalence point or theoretical end point. If both the acid and base are strong electrolytes, the resultant solution will be neutral and have a pH of 7. If either the acid or the base is a weak electrolyte, the salt will be hydrolyzed to some extent and the solution at the equivalence point will be either slightly alkaline or slightly acid.

The acid base indicators possess different colors according to the hydrogen ion concentration of the solution and the position of the color change interval in the pH scale varies widely with different indicators.

In aqueous solution an acid is dissociated into hydrogen ion and anion-

HCl → H+ + Cl

The hydrogen ion combines with water to give hydronium ion.

An alkali on dissociation in water gives hydroxyl ions,

NaOH ↔ Na+ + OH

The neutralization reaction is the reaction between an acid and a base to give a salt.

HCl + NaOH → NaCl + H2O

Procedure –

Preparation of 1 N Sodium Hydroxide-

Accurately weighed 40 gm sodium hydroxide pellets was taken in a 1000 ml volumetric flask and then 50 ml water was added, shaked and then the volume was made upto 1000 ml with water.

Standardization –

  1. 20 ml of 1 N Sodium hydroxide was pipette and taken in a conical flask.
  2. Then 2 drops of phenolphthalein was added to it.
  3. Now it was titrated with 1 N Hydrochloric acid until the color became colorless.

Observation – Suppose Burette reading = 16 ml

Calculation –                                  N1V1 = N2V2

Where N1 = Normality of unknown, V1 = Volume of unknown = 20 ml, N2 = Normality of known (1 N HCl) = 1, V2 = Volume of known (1 N HCl)= 16 ml

                                           N1 = N2V2 / V1 = 1 X 16 / 20 = 0.8 N

Result – Sodium hydroxide (1 N solution) was prepared and standardized. The normality was found to be 0.8 N.

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