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Test Method for Analysis of Total Acidity in Dilute and Strong Nitric Acid
Scope
This method is applicable of total acidity in dilute and strong nitric acid.
Principle of the method
 | Total Acidity is determined by titrating a weighed quantity of Nitric Acid against standard NaOH Solutions.
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| Since D.F.P.C.L process does not involve any other acid (viz., H2S04); this method is suitable, simple and less time consuming.
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| Nitrous gases present in the acid are included in the determination. |
Reference Document
Textbook of Quantitative Inorganic Analysis by Vogel, 4th Edition.
Reagents
1. Sodium Hydroxide 0.5 N solution.
2. Methyl red indicator (Na-SALT): 0.2 % Alcoholic Solution OR 50 mg of indicator dissolved in 100 ml of Distilled water.
Sample Size: Select sample amount that contains 25 mg of ACID.
Concentration
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Sample Size
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5% HN03 OR Less
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20 g.
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About 10% HN03
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10 g.
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About 20% HN03
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5 g.
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About 40% HN03
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3 g.
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About 60% HN03
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2 g.
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Apparatus
1. Weighing Bottle size 30 ml.
2. Pipette
3. Conical Flask
4. Burette
Procedure
| Take a clean glass weighing bottle (30-ml capacity). Put distilled water to it up to 1/4th level. Stopper it & weigh accurately.
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| Transfer appropriate amount of 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 & shake.
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| Titrate the contents of the flask against 0.5 N NaOH Solution.
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| End Point --------- > Colour Changes from red to yellow. |
Calculation
Total Acidity = V*N*6.3
WT %
Where,
V = ml of 0.5 N NaOH consumed
N = Actual Normality of 0.5 NaOH Solution.
Remarks
| If Sample contains more NO2, indicator may get discoloured. In such a case add few drops of indicator towards end point of titration.
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| A mixed indicator of methyl Red Methylene Blue Can Be used.
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| NaOH Solution 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 valve carefully and purge the line for 2 minutes to remove the line hold up. 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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