Carbon has two naturally occurring isotopes, carbon-12 and carbon-13. The more common isotope of carbon is carbon-12 with an abundance of 98.93% while carbon-13 has an atomic mass of 13.00335 u. Calculate the atomic mass of carbon-12 if the atomic mass of carbon is 12.0107 u.
A) 13.1 u
B) 13.0 u
C) 12.0 u
D) 12.8 u
E) 12.4 u

Question

Quizplus · Accepted Answer

Since carbon-12 has an abundance of 98.93%, it means that only 1.07% of carbon must be carbon-13. Therefore, to calculate the atomic mass of carbon-12, we can use the following formula:

Atomic mass of carbon-12 = (0.9893 x atomic mass of carbon-12) + (0.0107 x atomic mass of carbon-13)

Substituting the given values, we get:

atomic mass of carbon-12 = (0.9893 x 12.0107 u) + (0.0107 x 13.00335 u)

atomic mass of carbon-12 = 11.873 u + 0.139 u

atomic mass of carbon-12 = 12.012 u

Therefore, the atomic mass of carbon-12 is 12.012 u, which is closest to choice C (12.0 u).

Carbon Has Two Naturally Occurring Isotopes, Carbon-12 and Carbon-13