CHROMIUM OXIDE CONTENT
WET OXIDATION METHOD
APPARATUS
- Desiccator.
- Erlenmeyer flask – 300 ml capacity
- Conical flask – with stopper
- Heating element.
REAGENTS
- Distilled water.
- Concentrated sulfuric acid –relative density 1.84
- Perchloric acid 60-70 % (v/v)
- Phosphoric acid 85% (v/v)
- Starch solution –0.5%
- Standard Sodium thiosulfate solution – 0.1 N
- Potassium iodide solution -10%
PROCEDURE
- Sample the leather specimen to grounded form in leather mill machine.
- Weigh about 1 g of grounded test specimen and transfer it to 300 ml Erlenmeyer flask or Kjeldahl flask.
- Add 10 ml of concentrated nitric acid to the sample.
- Then add 8 ml sulfuric acid followed by 25 ml of Perchloric acid, cover the flask and heat to boiling on a low flame for about 45 minutes.
- As soon as, mixture turns to orange, lower the flame and heat slowly for 2 minutes.
- Then cool in air and finally rapidly in cold water by diluting the contents to about 200 ml.
- Again boil for 10 to 15 minutes using earthenware pebbles, to avoid bumping.
- Again cool and add 15 ml phosphoric acid followed by 20 ml of potassium iodide solution.
- Leave the solution in dark for 15 minutes.
- After 15 minutes, take the solution and add 5 ml of starch indicator.
- Titrate the solution with standard sodium thiosulphate solution to light green.
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.
REFERENCE: – IS 582:1970 (LC 10) – methods of chemical testing of leather.
