Question

What is the atomic mass of the element that consists of the following isotopes in the indicated natural abundances?

Isotope Isotopic mass (amu) Rel. abundance (%)

A 57.93 67.76
B 59.93 26.16
C 60.93 1.25
D 61.93 3.66
E 63.93 1.16

Express your answer to 3 sig figs and include the appropriate units

Answer 1

Answer : The atomic mass of the element is, 58.70 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`

As we are given that,

• Mass of isotope A = 57.93 amu

Percentage abundance of isotope A = 67.76 %

Fractional abundance of isotope A = 0.6776

• Mass of isotope B = 59.93 amu

Percentage abundance of isotope B = 26.16 %

Fractional abundance of isotope B = 0.2616

• Mass of isotope C = 60.93 amu

Percentage abundance of isotope C = 1.25 %

Fractional abundance of isotope C = 0.0125

• Mass of isotope D = 61.93 amu

Percentage abundance of isotope D = 3.66 %

Fractional abundance of isotope D = 0.0366

• Mass of isotope E = 63.93 amu

Percentage abundance of isotope E = 1.16 %

Fractional abundance of isotope E = 0.0116

Now put all the given values in above formula, we get:

`\text{Average atomic mass}=[(57.93* 0.6776)+(59.93* 0.2616)+(60.93* 0.0125)+(61.93* 0.0366)+(63.93* 0.0116)]`

`\text{Average atomic mass}=58.70amu`

Therefore, the atomic mass of the element is, 58.70 amu