Question

Caffeine has a molecular weight of 194.If it contains 28.9% by mass of Nitrogen, the number of atoms of Nitrogen in one molecule of caffeine is(pls give an explanation for necessary steps)

Answer 1

Molecular weight: Molecular weight of a compound is the sum of the atomic weight of all atoms present in the compound.

% by mass means the amount of element present in the 100 g of the compound.

Step 1: Calculating the mass of nitrogen in caffeine

Given:

The molecular weight of caffeine $=194u$

Mass of nitrogen$\left(N\right)=28.9$% by mass

Mass of nitrogen in $194u=\frac{28.9}{100}\times 194=56u$

Step 2: Calculating the number of the Nitrogen atom

Mass of one Nitrogen atom $=14u$

Hence, number of nitrogen atom $=\frac{56}{14}=4$