CHROMIC OXIDE (Leather Testing)

CHROMIC OXIDE CONTENT BY WET OXIDATION METHOD

SCOPE: - This standard prescribes a method for determining the chromium as Cr2O3 in leathers.



PRINCIPLE: - In this method, the trivalent chromium in the leather is oxidized with an oxidizing mixture containing Perchloric acid and sulphuric acid to the hexavalent chromium. Chromic oxide is then determined by iodometric titration of the hexavalent chromium..

REFERANCE: - IS 582:1970 (LC 10) - methods of chemical testing of leather.
APPARATUS:-
1. Dessicator.
2. Erlenmeyer flask – 300 ml capacity
3. Conical flask – with stopper
4. Heating element.
REAGENTS:-
1. Distilled water.
2. Concentrated sulfuric acid –relative density 1.84
3. Perchloric acid 60-70 % (v/v)
4. Phosphoric acid 85% (v/v)
5. Starch solution –0.5%
6. Standard sodium thiosulfate solution -0.1 N
7. Potassium iodide solution -10%

PROCEDURE:-
1. Sample the leather specimen to grounded form in leather mill machine.
2. Weigh about 1 g of grounded test specimen and transfer it to 300 ml Erlenmeyer flask or Kjeldahl flask.
3. Add 10 ml of concentrated nitric acid to the sample.
4. Then add 8 ml sulphuric acid followed by 25 ml of Perchloric acid, cover the flask and heat to boiling on a low flame for about 45 minutes.
5. As soon as, mixture turns to orange, lower the flame and heat slowly for 2 minutes.
6. Then cool in air and finally rapidly in cold water by diluting the contents to about 200 ml.
7. Again boil for 10 to 15 minutes using earthenware pebbles, to avoid bumping.
8. Again cool and add 15 ml phosphoric acid followed by 20 ml of potassium iodide solution.
9. Leave the solution in dark for 15 minutes.
10. After 15 minutes, take the solution and add 5 ml of starch indicator.
11. Titrate the solution with standard sodium thiosulphate solution to light green.



Name of Laboratory: INTERNATIONAL TESTING CENTRE, MSME, MEERUT
Document No: Doc-8b Document Name: Standard Operating Procedure
Issue No.:03 Issue Date: 10.01.2016 SOP No: ITC-LT 004 Page No:1/2
Amend No.:01 Amend Date: 30.01.2016 Prepared by :TM Approved by: CEO
Issue by: QM


CALCULATION:-


Chromium (as Cr2O3), percent by weight =    2.534 V N
W

Where,
V= volume in ml of standard sodium thiosulphate solution,
N= normality of standard sodium thiosulphate solution, and
W = weight in g of the material taken for the test.













Name of Laboratory: INTERNATIONAL TESTING CENTRE, MSME, MEERUT
Document No: Doc-8b Document Name: Standard Operating Procedure
Issue No.:03 Issue Date: 10.01.2016 SOP No: ITC-LT 004 Page No:1/2
Amend No.:01 Amend Date: 30.01.2016 Prepared by :TM Approved by: CEO
Issue by: QM


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