Question

caffeine has a molecular weight of 194 if it contains 28.9℅by mass of nitrogen.how many N atoms are there in one molecule of caffeine

Answer 1

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Answer 2

Answer : The number of nitrogen atoms are there in one molecule of caffeine, $24.088\times 10^{23}$

Solution : Given,

Molar mass of nitrogen = 14 g/mole

Molecular weight of caffeine = 194 g/mole

First we have to calculate the mass of nitrogen.

$\text{Mass of nitrogen}=194\times \frac{28.9}{100}=56.066g=56g$

Now we have to calculate the moles of nitrogen.

$\text{Moles of nitrogen}=\frac{\text{Given mass of nitrogen}}{\text{Molar mass of nitrogen}}=\frac{56g}{14g/mole}=4moles$

Now we have to calculate the number of nitrogen atoms are there in one molecule of caffeine.

As, 1 mole of nitrogen contains $6.022\times 10^{23}$ number of nitrogen atoms

So, 4 moles of nitrogen contains $4\times 6.022\times 10^{23}=24.088\times 10^{23}$ number of nitrogen atoms

Therefore, the number of nitrogen atoms are there in one molecule of caffeine, $24.088\times 10^{23}$