Limit test for iron

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BACKGROUND

In this limit test, the iron reacts with thioglycollic acid in the presence of citric acid and in alkaline medium develops a pale pink to deep reddish purple colour due to the ferrous compounds might be present in the sample.

As this test is very sensitive, citric acid 20% has been added which doesn’t permit the pptⁿ of iron by ammonia by forming a complex with it and the colour formed due to ferrous compound gets damaged by oxidising agents and alkalies.¹

Aim: Aim of this experiment is to carry out the limit tests for iron of the given samples.

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REQUIREMENTS

Apparatus: Nessler’s cylinder,

Glass Rod,

Analytical balance

Sample: Potassium bromide(1gm),

Sodium chloride(0.5gm),

Borax(0.5gm),

Sodium carbobate(0.2gm)²

Chemicals: Thioglycollic acid,

Iron free ammonia solution,

Iron free citric acid,

Distilled water

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PROCEDURE

The method for carrying out limit test for chloride requires; a standard and a test solution

Preparation of test solution

The specified amount of sample was taken and dissolved in some few ml of distilled water followed by addition of 2ml of 20% w/ citric acid and 0.1ml of thioglycollic acid, then the solution was made alkaline with iron free NH₃ solution, and the volume was made upto 50ml with distilled water.

Reaction

Preparation of standard solution

1ml of 0.1089% w/v of pot.sulphate was taken in a clean nessler’s cylinder to which few ml of distilled water and 2ml of dil.HCl were added². Then the volume was made upto 45ml with distilled water and barium sulphate 5ml was added at last , after which it was kept still for 5mins.

Reaction

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CONCLUSION

After performing the above test, it was observed that the samples are of pharmaceutical mark as the opalescence of the test samples are lesser tan tat of standard solution.

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REFERENCES

1. Chatwal GR. Pharmaceutical inorganic chemistry (vol- 1); 2016.
   
2. Indian pharmacopoeia; 2016.