Question

Carbon exists in nature as three isotopes. Given the atomic masses and relative abundance of the isotopes, what is the average atomic mass of carbon?

A.12.000 amu
B.12.011 amu
C.13.002 amu
D.13.003 amu
E.14.003 amu

Answer 1

The answer would be B, 12.011 AMU. You can calculate this by adding together the weights of each isotope based on their abundance.

12.000 x 0.9893 = 11.872
13.003 x 0.0107 = 0.13913
(C-14’s abundance is so low that the influence is negligible)

Atomic Mass by Abundance: 11.872 + 0.13913 = 12.0111.

Answer 2

Answer: The average atomic mass of carbon is 12.09 amu

Step-by-step explanation:

Solution : Given,

Mass of isotope C-12 = 12 amu

% abundance of isotope C-12= 98.93% = 0.9893

Mass of isotope C-13 = 13.003 amu

% abundance of isotope C-13 = 1.07% = 0.0107

Mass of isotope C-14= 14.003 amu

% abundance of isotope C-14 = 0.0000000001% =
`1* 10^(-12)`

Formula used for average atomic mass of an element :

`\text{ Average atomic mass of carbon}=\sum(\text{atomic mass of an isotopes}* {{\text { fractional abundance}})`

`\text{ Average atomic mass of an element}=\sum[(12*0.9893)+(13.003* 0.01707)+(14.003* 10^(-12))`

`\text{ Average atomic mass of an element}=12.09amu`

Therefore, the average atomic mass of carbon is 12.09 amu.