Question

Use the data given in the following table to calculate the molar mass of naturally occurring argon.

Isotope	Isotopic molar mass	Abundance
36Ar	35.96755 g mol-1	0.337%
38Ar	37.96272 g mol-1	0.063%
40Ar	39.9624 g mol-1	99.600%

Answer 1

The molar mass of the naturally occurring argon is equal to the weighted arithmetic mean of the various isotopes present in it. Then molar mass of argon

= {0.337 x 35.96755 g/mol + 0.063 x 37.96272 g/mol + 99.6 x 39.9624 g/mol}/{100}

= {12.121 g/mol + 2.392 g/mol + 3980.255 g/mol}/{100} = {3994.768 g/ml}/{100}

= 39.948 g/ml