AIM:- To perform limits test for iron.
Apparatus:- Nessler's cylinder, Glass rod, Measuring cylinder, pipette, dropper,
Chemicals required:- citric acid 20% w/v, ammonia 10%w/v,ferric ammonium sulphate,thioglycolic acid.
Apparatus:- Nessler's cylinder, Glass rod, Measuring cylinder, pipette, dropper,
Chemicals required:- citric acid 20% w/v, ammonia 10%w/v,ferric ammonium sulphate,thioglycolic acid.
- Iron free citric acid
20 % w/v solution of Citric acid.
20g of citric acid in 100 ml of water
Ammonia 10% w/v of ammonia in water.
Preparationo standard iron solution:-
• Weigh accurately 0. 1728 g of ferric ammonium sulphate and dissolve it in 10 ml of 0.1N sulfuric acid and make up to 1000 ml with water.
• 1ml = 0. 02 mg of Fe.
THEORY/Principal:-
The limit test for iron is based on the reaction of iron in ammonical solution in the presence of citric acid with thioglycolic acid. When a pale pink to deep reddish purple color is formed due to the ferrous thioglycote complex. The color produced from a specific amount of substance from test is compared with the color produced in standard solution by viewing vertically.
• Ferric ammonium sulphate is used as standard .
• The test is very sensitive ' interference of other metal cations is eliminated by using of 20 % w / v citric acid .
• The iron free citric acid is used to complex metal cations other than iron if any .
• Ferrous thioglycollate complex is colorless in acidic or neutral solutions.
• Only in the presence of alkali pale pink color will be produced.
• citric acid forms ammonium citrate buffer when ammonia is added to make alkalinewhich in turn stabilizes the complex formed.
1. Pipette out 2 ml of standard Iron solution into the Nessler's cylinder marked as standard
2. Dilute it to 40 ml with distilled water.
3. Add 2 ml of 20 % w/v solution of iron free citric acid
4. Add 0.1ml of thioglycolic acid.
5. Mix and make alkaline with iron free ammonia solution and dilute to 50ml with water
6. Immediately stir with a glass rod and allow it to stand for five minutes.
◆Test Solution
1. Dissolve the specified quantity of given sample in distilled water in Nessler's cylinder marked as test.
2. Dilute it to 40 ml with distilled water.
3. Add 2 ml of 20 % w/v solution of iron free citric acid.
4. Add 0.1ml of thioglycolic acid.
5. Mix and make alkaline with iron free ammonia solution and dilute to 50ml with water.
6. Immediately stir with a glass rod and allow it to stand for five minutes.
Observation:-
Sample I [Pass Sample]:
The color produced in the test solution is less than standard solution.
Observation:-
Sample I [Pass Sample]:
The color produced in the test solution is less than standard solution.
Result:-
The given substance passes the limit test for iron when compared with that of a standard substance.
See Video :- limit test for iron
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