Determination Of Nitrogen Content Of Rubber

AIM:
To determine the nitrogen in raw natural rubber using Kjeldahl semi micro method.
CHEMISTRY:
This is done to find the protein content in raw natural rubber. If protein content is greater, nitrogen is greater & if protein content is lesser, nitrogen is lesser.
PRINCIPLE:
A known mass of the sample is digested with a mixture of H₂SO₄, catalytic amounts of CuSO₄ & Se.The end product is distilled after making it alkaline. The distilled product is absorbed in H₃BO₃, followed by titration with standard acid.
REQUIREMENTS:

• Kjeldahl distillation unit
• Balance
• Nitrogen Tube
• Semi micro burette
• Measuring cylinder 10ml
• Conical flasks 100ml

REAGENTS:

• 67% NaOH solution
• Methyl orange indicator
• Phenolphthalein indicator
• 0.1N Na₂CO₃ solution
• 0.1N NaOH solution
• Boric acid solution
• Catalyst mixture ( 15:2:1)
• 0.01N H₂SO₄

PROCEDURE:

• Weigh accurately about 0.1gm of the blended rubber into the Nitrogen tube.
• Note the weight taken.
• Add 3ml con H₂SO₄ & 0.65 gm of catalyst mixture into the nitrogen tube.
• Boil gently until the contents become clear green in colour with no yellow tint.

CARE SHOULD BE TAKEN WHILE DOING THIS EXPERIMENT..ALSO THE ABOVE TEST SHOULD BE DONE IN A SEPARATE ROOM PROVIDED IN THE LAB..NO PERSON SHOULD STAND NEAR TO IT..THE VAPOURS FROM IT ARE DANGEROUS TO HEALTH.

• Cool & transfer the contents with small portion of distilled water, to the distillation apparatus, which has been previously steamed out for 30 minutes.
• Add 10ml 67% NaOH solution to the flask.
• Take 10ml H₃BO₃ solution in the 100ml flask.
• Place the flask in the receiver.
• Pass steam through the apparatus till 50- 75ml distillate is collected in the receiver.
• Colour of H₃BO₃ changes from violet to green.
• Remove the flask , titrate with 0.01N H₂SO₄ till the colour changes from green to violet.
• Note the burette reading.

RESULT:

From the weight of the sample, normality of H₂SO₄ & the burette reading for sample, the % of nitrogen in rubber can be calculated...