Question

The element nitrogen has an atomic weight of 14.0 and consists of two stable isotopes nitrogen-14 and nitrogen-15. The isotope nitrogen-14 has a mass of 14.0 amu and a percent natural abundance of 99.6 %. The isotope nitrogen-15 has a percent natural abundance of 0.370 %. What is the mass of nitrogen-15? amu

Answer 1

Answer : The mass of nitrogen-15 is, 15.1 amu

Explanation :

Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

`\text{Average atomic mass }=\sum_(i=1)^n\text{(Atomic mass of an isotopes)}_i* \text{(Fractional abundance})_i` .....(1)

For
`^(14)\textrm{N}` isotope:

Mass of
`^(14)\textrm{N}` isotope = 14.0 amu

Fractional abundance of
`^(14)\textrm{N}` isotope = 99.6 % = 0.996

For
`^(15)\textrm{N}` isotope:

Mass of
`^(15)\textrm{N}` isotope = ?

Fractional abundance of
`^(15)\textrm{N}` isotope = 0.370 % = 0.00370

Average atomic mass of nitrogen = 14.0 amu

Now put all the given values in equation 1, we get:

`14.0=[(14.0* 0.996)+(\text{Atomic mass of }^(15)\textrm{N}* 0.00370)]`

`\text{Atomic mass of }^(15)\textrm{N}=15.1amu`

Therefore, the mass of nitrogen-15 is, 15.1 amu