Question

An alkaloid contains $17.28\% $ of nitrogen and its molecular mass is 162. The number of nitrogen atoms present in one molecule of alkaloid is:
A. Five
B. Four
C. Three
D. Two

Answer 1

Hint: An alkaloid is a naturally occurring organic compound that is basic and contains at least one nitrogen compound. It can be drugs and poisons such as morphine, atropine etc. The given alkaloid has $17.28\% $ of nitrogen, so we can write as $\% of\;{{a nitrogen = }}\dfrac{{given\;{{mass}}}}{{total\;{{weight \;of\; molecule}}}} \times 100$
There are different formulas to find the percentage of sulphur, oxygen and halogens present in different molecules.

Complete step by step answer:
By substituting the values in the above equation,
$17.28 = \dfrac{{mass}}{{162}} \times 100$
Therefore, the mass of nitrogen can be calculated by cross multiplication.
$weight\;{{of }}{{{N}}_2} = \dfrac{{17.28 \times 162}}{{100}}$
$ = 27.99$
$ = 28$
Thus, we got the weight of Nitrogen in the given alkaloid is 28g.
So, the number of nitrogen atoms in one molecule of the alkaloid can be found out by the formula
$No\;{{of\; atoms = }}\dfrac{{weight}}{{molar\;weight}}$
We know that the molar weight of nitrogen is 14.
$No\;{{of \;atoms = }}\dfrac{{28}}{{14}} = 2$
Thus, the number of nitrogen atoms present in one molecule of alkaloid is two.

So, the correct answer is Option D.

Note: The percentage of nitrogen can be found out also by kjeldahl method.
Here, the formula is $\% \;of\;{{N = }}\dfrac{{{{1}}{{.4V}} \times {{N}}}}{W}$,
Where V is the volume of acid used in titration, N is the normality and W is the weight of the sample, in this case of alkaloid. This formula is used when volume of the sample is given. The limitation of the Kjeldahl method is that it cannot be used to find the percentage of nitrogen in azo compounds, nitro groups or in rings.