Learn the limit test of chloride through a laboratory experiment or practical.
Aim:
To perform the limit test of chloride.
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Requirements:
Glasswares and miscellaneous: Nessler cylinders, measuring cylinder, pipette, dropper, rubber stopper test tube stand, glass rod, and balance.
Chemicals: 5% silver nitrate solution (AgNO3), 10 % or dilute nitric acid solution (HNO3), sodium chloride (NaCl).
Reference: Indian Pharmacopoeia (IP) 2010.
Principle of limit test for chloride:
The principle of limit test for chloride is based on the chemical reaction between AgNO3 and soluble chlorides in the presence of dil. HNO3 to produced opalescence of silver chloride (AgCl) is produced.
The produced opalescence of the sample is compared with a standard solution. The sample passes the test if its opalescence is less than the standard. It fails the test if it exceeds the standard.
Preparation of chemicals:
How to prepare dilute nitric acid:
Take 106.00 ml of concentrated HNO3 using a pipette, dilute in 1000 ml of distilled water in a volumetric flask, and properly mixing it.
How to prepare 5 % w/v silver nitrate solution:
Take 05.00 gm of AgNO3 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.
How to prepare 0.05845% standard sodium chloride solution:
Take 0.05845 gm of NaCl 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.
The procedure of limit test for chloride:
Standard:
- Take 01.00 ml of standard sodium chloride solution using a pipette into a Nessler cylinder and label it as standard.
- Add 10.00 mL of dilute nitric acid to the above preparation.
- Dilute it to 50.00 ml with distilled water.
- Then add 1ml of prepared 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:
- Prepare a solution as recommended in the specific monograph and transfer it to a Nessler cylinder, or dissolve the specified quantity of the substance in water and label it as a test.
- Add 10.00 ml of dilute nitric acid.
- Dilute it to 50.00 ml with distilled water.
- Then add 1ml of prepared silver nitrate solution.
- Stir immediately with a glass rod and let stand for five minutes by protecting from light.
- Observe this test preparation under a black background.
Observation:
|
Pass Sample |
Fail Sample |
|
Observation |
|
|
The test solution produces less opalescence than the
standard solution. |
The test solution produces more opalescence than the
standard solution. |
|
Inference |
|
|
As compared to a standard substance, the given substance
passes the test for chloride as per IP. |
As compared to a standard substance, the given substance fails
the test for chloride as per IP. |
Result:
The sample passes/fails the limit test as per Indian Pharmacopoeia.
Precautions:
- Because chloride in tap water will interfere with the result, distilled water must be used.
- It is not recommended to use the same glass rod for the standard and the sample, as this will interfere with your observation.
- Because silver nitrate is photosensitive, it should be kept in an amber-colored bottle (Protect from light).
- When silver nitrate comes into touch with the skin, it produces black spots.
FAQ (Frequently Asked Questions):
What is limit test and its importance?
In chemistry, the limit test is a quantitative or semi-quantitative test used to detect and control small amounts of impurity in a substance. A limit test is used to determine the amount of inorganic contaminants in a compound.
Why nitric acid is used in the limit test for chloride?
Nitric acid is added to the chloride limit test to make the solution acidic and to helps silver chloride precipitation, which causes the solution to become turbid at the end of the process.
What is the principle of the modified limit test of chloride?
The modified limit test of chloride is based on the same principle as the limit test of chloride. The modified limit test of chloride is used for a color compound that cannot be tested with a normal test.
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