Deepak Fertilisers and Petrochemicals Corporation Ltd.- Testing for HNO2 content

Deepak Fertilisers & Petrochemicals Corporation Ltd.

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A leading manufacturer of industrial chemicals including methanol, nitric acid and carbon dioxide.

The largest Indian manufacturer of ammonium nitrate.

"Mahadhan" brand fertilisers are effective for a wide variety of crops.

Test method for Analysis of HNO₂ Content in Concentrated Nitric Acid

Scope
This method is applicable for measuring of HN02 content in CAN.

Principle of the Method
CNA Sample is titrated against 0.1 N KMnO4 in presence on 20% H2S04

HNO₂ Gets Oxidised to HNO₃ and in the process Mn (7+) is reduced to Mn (2+). This leads to Discoloration of KMnO₄ Solution.

5HNO₂+2KMnO₄+3H₂SO₄=> K₂SO₄+2MnSO₄+5HNO₃+3H₂O i.e. 5NO₂^- +2MnO_4- +6H = 2Mn+5NO_3- +3H₂O.

Reference Document
Textbook of Quantitative Inorganic Analysis by Vogel, 4^th Edition.

Reagents
KMn04 0.1 N Solution 20% H2S04.

Apparatus

1. Erlenmeyer Flask Size 250 ml.
2. Pipette 25 ml.
3. Burette

Procedure
Take 100 ml Distilled water in an Erlenmeyer flask. Add 25 ml of 20 % H2S04. Shake well & Add 25 ml CNA Sample. Quickly Titrate against 0.1 N KMn04 Solution to a distinct pink colour that persists for at least three minutes.

Calculation
%HNO₂=(ml of KMnO₄)*N of KMnO₄*.0235*100 / (Simple Volume)*(Density of CNA )

Remarks

1. Density of CNA should be determined separately.

2. If CNA contains more HNO₂ (Evident from Brown Colour) take 10 ml of sample.

3. Owing to the slow self-decomposition of CNA the HNO₂ content increases during storage.

4. 0.1 N KMnO₄ should be standardised daily with previously dried A.R. Grade Oxalic Acid / Mono sodium oxalate.

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