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Test Method for Analysis of Nitric Acid Content in Concentrated Nitric Acid
Scope
This method is applicable of HN 03 content in CAN/WNA (Total Acidity method).
Principle
 | HNO3 is Estimated as total acidity minus HNO2 Content.
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| Total Acidity is determined by titrating a weighed quantity of acid against standard NaOH solution.
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| Since D.F.P.C.L. Process does not involve any other acid (Viz. H2SO4), This method becomes most suitable, simple, and less time consuming. |
Reference Document
Textbook of Quantitative inorganic Analysis by Vogel, 4th Edition.
Reagents
| Sodium Hydroxide : 0.5 N solution
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| Sodium Hydroxide : 0.2 N solution
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| Methyl Red Indicator (Na-SALT): 0.2% ALCOHOLIC SOLN. |
Apparatus
1. Glass Burette
2. Glass Beaker Size 500 ml.
3. Stoppered weighing bottle size 5 ml
Procedure
| Take a clean weighing bottle. Put Distilled water to it upto 1/4th level. Stopper it and weigh accurately.
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| Transfer about 1g of CAN sample to the weighing bottle and quickly stopper it. Weigh again. Difference in weight will give weight of sample.
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| Take about 100 ml distilled water in a wide mouth conical flask. Insert the weighing bottle into the conical flask. Remove stopper and quickly dip both bottle and stopper in water. Swirl the contents. Add 5 drops of methyl Red Indicator and shake.
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| Titrate the contents of the flask initially against 0.5 N NaOH Solution. Just Before the end point; use 0.2 N NaOH for titration.
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| End Point ----- > Color changes from Red to yellow. |
Calculation
Total Acidity = [(V1*N1)+(V2*N2)]*6.3 / Sample weight
Wt %
Where: V1= Volume of 0.5 N NaOH Consumed
V2= Volume of 0.2 N NaOH Consumed
N1=Actual Normality of 0.5 N NaOH Solution
N2=Actual Normality of 0.2 n NaOH solution
Remarks
1. If sample contains more NO 2, Indicator may get discolored; in such a case add few drops of indicator towards the end point of titration.
2. After determining HNO2 content; Convert it into HNO3 (Multiply by 1.37) and Deduct it from total acidity to get HNO3 Content of CNA.
HNO3 Content = total acidity - (HNO2*1.37)
3. NaOH solutions should be standardised daily with previously dried A.R Grade Potassium Hydrogen Phthalate.
Sampling
| Sampling point should have a tray containing flowing water to wash spilled nitric acid.
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| Open the value carefully and purge the line for 2 minutes to remove the line holdup. Close the valve.
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| Put the sample bottle exactly below the sample point and insert the bottle in such a way that the sample tube is dipped into the bottle.
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| Open the valve carefully; collect some sample and close the valve again. Rinse the bottle.
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| Repeat rinsing procedure once again and then collect about 250 ML sample. Stopper the bottle immediately. |
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