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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: gpapachs on June 26, 2016, 12:04:19 PM

Title: kjeldahl method
Post by: gpapachs on June 26, 2016, 12:04:19 PM

Good afternoon,

I am new at the forum.

Could somebody please explain me the method kjeldahl method accorning to the monography??

I need help with the type to calculate the nitrogen content.

Can somebody explain what is F: the factor of 0,1N sodium hydroxide in the following type :

N%= M*0,01*F*(V0-V)/n*s  *  100

Thank you in advance

Title: Re: kjeldahl method
Post by: Borek on June 26, 2016, 01:44:31 PM

Hard t comment not knowing what all other symbols mean. In general, try to derive the formula the simple stoichiometry and the meaning should become obvious.

Title: Re: kjeldahl method
Post by: gpapachs on June 26, 2016, 02:29:35 PM

Thanks for the answer...

I have all the other parameters calculated.

I just cannot understand what F is.

At the method it is described as : the factor of 0.1N sodium hydroxide volumetric solution

Could it be a constant??

Could it be the extract concentration of the sodium hydroxide solution that was used??

Having any idea???

Title: Re: kjeldahl method
Post by: Borek on June 26, 2016, 04:16:28 PM

Perhaps it is defined globally somewhere else in the book. Sorry, but it is quite random without a context.

Title: Re: kjeldahl method
Post by: Starlord on July 02, 2016, 07:38:42 PM

I am assuming you are attempting to calculate Nitrogen (atomic mass 14) content using distillation?

Whilst distillation time will specific to your application/sample type - I would estimate this at approx 5mins

The calculation:
(mls 0.1 N Sulphuric acid - mls 0.1 N Sodium Hydroxide) x 14 = ppm N  (if 100mls sample was used)


Is this what you're after?

Provide some more info such as sample amount and typical expected titration and I might be better able to help

Title: Re: kjeldahl method
Post by: Starlord on July 02, 2016, 07:46:09 PM

For example, if I was attempting to determine N in 100mls of sample I would:

Distill into indicator with for example 20mls 0.1 N sulphuric acid
Titrate using 0.1 N Sodium Hydroxide ( say we need 13 mls)

Calculate:

(20 - 13) x 14 = 98ppm N

Convert ppm to %     divide by 10,000

= 0.0098% N