Question

If isotopic distribution of $C-12$ and $C-14$ is $98\%$ and $2\%$ respectively, then the number of $C-12$ atoms in $14$ g of carbon is:

• A. $3.011\times {10}^{23}$
• B. $6.885\times {10}^{23}$
• C. $12.044\times {10}^{23}$
• D. none of these

Answer 1

Answer: (B)

$6.885\times {10}^{23}$

Amount given for carbon $=14gm$.

molecular weight of $C^{12}=12$ gm/mole.

$\therefore$ Number of moles $=\frac{14}{12}=\frac{7}{6}=1.166$ moles.

Number of carbon atoms $=$ moles $\times$ Avagadro number.

$=1.166\times 6.023\times {10}^{23}$

$=7.022\times {10}^{23}$.

% of occurrence of $C^{12}=98$% $=98$.

So, number of $C^{12}$ atoms $=7.02\times {10}^{23}\times 0.98=6.88\times {10}^{23}$.