Question

Calculate the average atomic mass of argon to two decimal places, given the following relative atomic masses and abundances of each of the isotopes: argon-36 (35.97 u; 0.337%), argon-38 (37.96 u; 0.063%), and argon-40 (39.96 u; 99.600%)

Answer 1

Answer:

39.95 u

Explanation:

The formula for the calculation of the average atomic mass is:

$Average\ atomic\ mass=(\frac {\%\ of\ the\ first\ isotope}{100}\times {Mass\ of\ the\ first\ isotope})+(\frac {\%\ of\ the\ second\ isotope}{100}\times {Mass\ of\ the\ second\ isotope})+(\frac {\%\ of\ the\ third\ isotope}{100}\times {Mass\ of\ the\ third\ isotope})$

Given that:

For first isotope, Argon-36:

% = 0.337 %

Mass = 35.97 u

For second isotope, Argon-38:

% = 0.063 %

Mass = 37.96 u

For third isotope, Argon-40:

% = 99.600 %

Mass = 39.96 u

Thus,  

$Average\ atomic\ mass=\frac{0.337}{100}\times {35.97}+\frac{0.063}{100}\times {37.96}+\frac{99.600}{100}\times {39.96}=0.1212189+0.0239148+39.80016=39.9452937$

Average atomic mass = 39.95 u