Question

Carbon occurs in nature as a mixture of carbon -12 and carbon-13. the average atomic mass of carbon is 12.011. what is the percentage abundance of carbon-12 in nature ?

Answer 1

I have used the formula for calculating average atomic mass.

Answer 2

Answer: Percentage abundance of Carbon -12 isotope is 98.9%

Explanation: We are given average atomic mass of carbon to be 12.011 amu.

We take fractional abundance of Carbon-12 isotope = x

Mass of Carbon-12 isotope = 12 amu

Fractional isotope of Carbon-13 isotope = (1 - x)

Mass of Carbon-13 isotope = 13 amu

Using the formula:

$\text{Average atomic mass of an element}=\sum_{i=1}^n(\text{Atomic mass})_i(\text{Fractional abundance})_i$

Putting all the values in above equation, we get

$12.011=(12)(x)+(13)(1-x)$

x = 0.989

To convert fractional abundance into percentage abundance, we multiply it by 100.

$\% \text{ abundance}=0.989\times 100$

Percentage abundance of carbon-12 isotope = 98.9 %