PRACTICAL-ASSAY OF AMMONIUM CHLORIDE BY ACID BASE TITRATION

Object – To perform the assay of Ammonium chloride by acid base titration

Reference – 1. Siddiqui A.A. & Ali M., Practical Pharmaceutical Chemistry, CBS publishers and distributors, New Delhi, I edition, 1997, 22-23

  1. Rao G.D., Practical pharmaceutical analysis, Birla publications Pvt. Ltd., Delhi, II edition, 2007-08, 33

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

Chemicals required – ammonium chloride, distill water, formaldehyde solution, phenolphthalein indicator, sodium hydroxide solution

Theory – Acid base titration or neutralization titration involves neutralization of acid with base or base with acid and the end point is determined by means of indicator.

Acidimetry titration – it is a direct or residual volumetric analysis of a base with a standard acid. Direct titration is performed by introducing a standard acid solution gradually from a burette into a solution of base being assayed till the end point is obtained e.g. assay of sodium bicarbonate. Residual titration is used when the rate of reaction between a basic compound with an acid is slow. In this, the solution of the base is treated with an excess of accurately measured standard acid and excess acid is subsequently titrated with standard base e.g. assay of zinc oxide.

Alkalimetry titration – it is an estimation of acid/acidic drugs by titration with standard alkali. It also includes direct titration and residual/back titration methods as in acidimetry. Assay of ammonium chloride comes under direct titration method of Alkalimetry titration.

Ammonium chloride is an example of diuretic and systemic acidifier. The assay of ammonium chloride is based on the principle of formal titration. The formal titration is done in the presence of formaldehyde. When ammonium chloride is treated with formaldehyde (HCHO), HCl is liberated. The liberated hydrochloric acid is btitrated with a standard solution of sodium hydroxide using phenolphthalein indicator.

Procedure

  1. 1 gm of ammonium chloride was accurately weighed and dissolved in 20 ml water.
  2. 5 ml formaldehyde solution was added.
  3. After two minutes, titration was started slowly with 0.1 N Sodium hydroxide (given below) solution by using phenolphthalein indicator till pink color was obtained.
Preparation of 100 ml 0.1 N NaOH
Normality Volume Amount Dissolved in
1 N 1000 ml 40 gm 1000 ml
0.5 N 1000 ml 20 gm 1000 ml
0.1 N 1000 ml 4 gm 1000 ml
0.1 N 500 ml 2 gm 500 ml
0.1 N 100 ml 0.4 gm = 400 mg 100 ml

 

The reaction involved is-

HCl + NaOH           →      NaCl + H2O

Equivalent Factor – 1 ml of 0.1 N NaOH is equivalent to 0.005349 g of NH4Cl

Observation table –

S.NO. VOLUME OF AMMONIUM CHLORIDE SOLUTION IN ML INITIAL BURETTE READING FINAL BURETTE READING VOLUMJE OF 0.1 N SODIUM HYDROXIDE CONSUMED IN ML
1 25 50 33 (suppose) 17 (suppose)

 

 

Calculation –

Percentage purity of ammonium chloride =

Volume of 0.1 N sodium hydroxide x equivalent factor x 100 x normality of sodium hydroxide (actual)

Weight of ammonium chloride in grams x normality of sodium hydroxide (expected)

17 x 0.005349 x 100 x 0.1

=   ———————————-

  • x 0.1

= 0.05349 x 17 / 0.01 = 0.909 / 0.01 = 90.9%

Result – Assay of Ammonium chloride by acid base titration was carried out and the percentage purity was found 90.9%.

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