Learn the limit test for chlorides for water-insoluble substances through a laboratory experiment or practical.
Aim:
To perform the limit test for chlorides for water insoluble activated charcoal
Sample: Activated charcoal
Requirements:
Glasswares and miscellaneous: Nessler cylinders, measuring cylinder, pipette, pipette bulb, dropper, test tube stand, glass rod, volumetric flask, and balance.
Chemicals: silver nitrate (AgNO3), nitric acid (HNO3), and sodium chloride (NaCl).
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Principle:
The test opalescence produced by chloride impurities reacting with AgNO3 is compared to the standard opalescence produced by a known amount of chloride reacting with silver nitrate. If other impurities are present, a dilute HNO3 solution is used to dissolve them.
The precipitate formed is AgNO3 insoluble in dilute HNO3 solution and provides opalescence. The key objective here is to determine chloride impurities in charcoal rather than actual charcoal. Chloride salts are generally water-soluble. Chloride salt dissolves when charcoal is treated with H2O, however charcoal does not. As a result, the suspension filtrate is used for the limit test for chloride.
Preparation of reagents:
Preparation of dilute HNO3:
Take 10.60 ml of concentrated HNO3 using a pipette, dilute in 100 ml of distilled water in a volumetric flask, and properly mixing it.
Preparation of 0.1M AgNO3:
Take 17.00 gm of silver nitrate and dissolve in 70 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume with distilled water to 100 ml. Light-resistant containers should be used for storage.
Preparation of 0.0824% w/v standard NaCl solution:
Take 0.0824gm of sodium chloride and dissolve in 50 ml of distilled water in a volumetric flask, and properly mixing it. Once it has completely dissolved, make up the volume with distilled water to 100 ml.
Preparation of 25 ppm standard NaCl solution:
Take 05 volumes of 0.0824% w/v sodium chloride solution using a pipette and dilute to 100 volumes of distilled water in a volumetric flask.
Procedure:
Standard opalescence:
- Take 10.00 ml of 25 ppm chloride standard solution using a pipette into a Nessler cylinder and label it as standard.
- Add 05.00 ml of water.
- Add 10.00 mL of dilute HNO3 solution to the above preparation and dilute to 50 ml with water.
- Then add 01.00 ml of prepared 0.1 M silver nitrate solution.
- Stir immediately with a glass rod and let stand for five minutes by protecting from light.
- Observe this standard preparation under a black background.
Test opalescence:
- Take 03.00 gm of activated charcoal in 75.00 ml distilled water, boil it for 5 minutes then cool.
- Make up the volume with distilled water to 100 ml and filter.
- Take 06.00 ml of the filtrate using a pipette into a Nessler cylinder and label it as a test.
- Add 10.00 mL of dilute HNO3 solution to the above preparation and dilute to 50 ml with water.
- Then add 01.00 ml of prepared 0.1 M silver nitrate solution.
- Stir immediately with a glass rod and let stand for five minutes by protecting from light.
- Observe this standard preparation under a black background.
Observations:
The test solution produces less or same or more opalescence than the standard solution.
Results:
The sample passes/fails the limit test as per Indian Pharmacopoeia.
FAQ (Frequently Asked Questions):
What is the inference for the chloride test?
When compared to a standard solution, the provided substance passes or fails the chloride limit.
Limit test of chloride is based on which reaction?
The chloride limit test is based on the reaction of soluble chloride with AgNO3 in the presence of dilute HNO3 to form AgNO3, which appears in the solution as solid particles.
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