Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: nova343 on December 24, 2023, 08:22:18 PM
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During estimation of nitrogen present in an organic compound by Kjeldahl’s method, the ammonia evolved from 0.5 g of the compound in Kjeldahl’s estimation of nitrogen, neutralized 10 mL of 1 M H2SO4. Find out the percentage of nitrogen in the compound.
I will explain how i solved this, please help me find my mistake
first i calculated the number of moles of H2S04 involved using the given volume and concentration.
it came out to be 10-2 moles.
In reaction between ammonia and H2SO4, for every 1 mole of sulphuric acid, there are 2 moles of ammonia reacting with it.
so, the number of moles of ammonia must be 2 x 10-2 moles.
ammonia has nitrogen to hydrogen ratio as 1:3.
which means the number of moles of nitrogen atoms is (2 x 10-2)/4.
which is 5 x 10-3
1 mole of nitrogen atom would have a mass of 14 grams which means the mass of nitrogen here is 5 x 10-3 x 14 grams.
which will be 7 x 10-2
the mass of the organic compound is 0.5 gram.
so, to calculate the percentage of nitrogen i did ((7 x 10-2)/0.5) x 100
which comes out to be 14 percent
the answer key says that it is 56 percent
where did i go wrong?
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ammonia has nitrogen to hydrogen ratio as 1:3.
which means the number of moles of nitrogen atoms is (2 x 10-2)/4.
Think it over.
Is there really 1/4th of mole of N atoms in a mole of the ammonia?
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Ah, yes you right
1 molecule of ammonia will have 1 nitrogen and 3 hydrogen
which means 1 mole of ammonia will have 1 mole of ammonia and 3 moles of hydrogen.
Thanks a lot for the insight!
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Who had thought this
which means 1 mole of ammonia will have 1 mole of ammonia
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i intended to write 1 mole of nitrogen and 3 moles of hydrogen, somehow managed to write ammonia twice