Three isotopes of argon occur in nature – 36 18ar, 38 18ar, 40 18ar. calculate the average atomic mass of argon to two decimal places, given the following relative atomic masses and the abundances of each of the isotopes: argon36 (35.97 amu; 0.337%), argon-38 (37.96 amu; 0.063%), argon-40 (39.96 amu; 99.600%).

39.95amu

Explanation:

Given parameters:

Relative atomic mass of Ar-36 = 35.97amu    abundance = 0.337%

Relative atomic mass of Ar-38 = 37.96amu     abundance = 0.063%

Relative atomic mass of Ar-40 =  39.96amu     abundance = 99.600%

Unkown:

Relative atomic mass of Ar = ?

Solution:

The relative atomic mass is the average mass of all the isotopes of an element. To solve for the average atomic mass, we use the expression below:

      RAM = m₃₆α₃₆ + m₃₈α₃₈ + m₄₀α₄₀

where m is the mass of the isotope

           α is the abundance of the isotope

 RAM of Argon = ( x 35.97) + ( x 37.96) +( x 39.96)

  RAM of Argon = 39.95amu

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