Nitrogen has two isotopes. One has an atomic mass of 14.003

amu and a relative abundance of 99.63% while the other

isotope has an atomic mass of 15.000 amu and a relative

abundance of 0.37%. What is the average atomic mass for

nitrogen?

a

14.456 amu

b

14.778 amu

C 14.993 amu

d 14.007 amu

d = 14.007 amu

Explanation:

Abundance of N¹⁴ = 99.63%

Abundance of N¹⁵ = 0.37%

Atomic mass of N¹⁴ = 14.003 amu

Atomic mass of N¹⁵ = 15.000 amu

Average atomic mass = ?

Solution:

Average atomic mass = (abundance of 1st isotope * its atomic mass) + (abundance of 2nd isotope * its atomic mass) / 100

Average atomic mass = (14.003 * 99.63) + (15.000 * 0.37) / 100

Average atomic mass = 1395.12 + 5.55 / 100

Average atomic mass = 1400.67 / 100

Average atomic mass = 14.007 amu.