Question

The isotopic abundance of C-12 and C-14 is 98% and 2% respectively. What would be the number of C - 14 isotope in 12 g carbon sample?

• A. $1.032\times {10}^{22}$
• B. $3.01\times {10}^{23}$
• C. $5.88\times {10}^{23}$
• D. $6.02\times {10}^{23}$

Answer 1

Answer: (A)

$1.032\times {10}^{22}$

Isotopic abundance of $C-12$ is $98$%

Isotopic abundance of $C-14$ is $2$%

Average atomic mass $=\frac{Massnumber\times Relativeabundance+Massnumber\times Abundance}{100}$

$=\frac{98\times 12+2\times 14}{100}$

$=12.04grams$

So, in $100$ grams of carbon sample, $C-14$ isotope will be $2$ grams since it is $2$% in abundance.

$\therefore$ in $12$ grams sample, $C-14$ isotope will be $=\frac{12\times 2}{100}=0.24grams$

$1$ mole of any compound has $N_A$ number of atoms i.e $6.02\times {10}^{23}$.

So, $C-14$ isotope will be $1.032\times {10}^{22}$