Assay of Ammonium Chloride

 AIM:

To determine the percentage purity of given sample of ammonium chloride.

REFERENCE:

1. Indian Pharmacopoeia -1985, volume I,

2. Practical pharmaceutical inorganic chemistry, Dr. G.Devalo Rao

3. Practical pharmaceutical chemistry by Anees Ahamed Siddiqui and Mohammed Ali

CHEMICALS USED:

Ammonium chloride, NaOH, Oxalic acid, formaldehyde

Ammonium Chloride: 

Ammonium chloride is a by-product of sodium carbonate. Ammonium chloride has diuretic and expectorant effects. In its pure form, it is crystalline salt, white. This compound is highly water-soluble and mildly acidic. Ammonium chloride is used in veterinary medicine for the prevention of urinary stones in sheep, goats, and cattle.

Properties of Ammonium Chloride

NH4Cl	Ammonium Chloride
Molecular Weight/ Molar Mass	53.491 g/mol
Density	1.53 g/cm³
Boiling Point	520 °C
Melting Point	338 °C

PRINCIPLE:

Ammonium chloride is assayed by indirect assay method. The sample is dissolved in water and treated with previously neutralised formaldehyde solution.(Methyleneimine is formed which polymerises to form Hexamine). This results in the quantitative liberation of HCl equivalent to NH4Cl. The liberated HCl is titrated with the standard solution of NaOH using phenolphthalein as indicator, appearance of pale pink colour is the indication of end point.

4NH4 Cl + 4H2O ---> 4NH4OH + 4HCl

4 NH4OH + 6HCHO ---> (CH2)6N4 + 10 H2O

4HCl + 4NaOH ---> 4NaCl + 4H2O

PROCEDURE:

Standardisation of 0.1 NaOH

Weigh accurately 0.63 g of oxalic acid into a 100 ml volumetric flask and make up to 100 ml volume with distilled water. Pipette out 20 ml solution and titrated with 0.1 M NaOH using phenolphthalein as indicator. Continue the titration to get the concordant value. 

ASSAY OF AMMONIUM CHLORIDE

Assay of NH4Cl

Weigh 0.1gm of NH4Cl dissolve in 20 ml of H2O and add a mixture of 5 ml of previously neutralized formaldehyde solution and 20 ml water. After 2 minutes the contents of the conical flask is titrated against 0.1N NaOH using phenolphthalein as indicator. End point is the appearance of permanent pale pink colour.

Each ml of 0.1N NaOH is equivalent to 0.005349 gm of NH4Cl. Percentage purity can be determined by the following formula.

           Titre value x Equivalent wt factor x Normality of NaOH(actual)

% = -------------------------------------------------------------------------------------- x 100

             Weigh of sample x Normality of titrant (expected)

REPORT: The percentage purity of the given sample of ammonium chloride