Question

Calculate the average atomic mass of a sample of a mixture of argon (Ar). The mixture is 90% argon- 36 and 10% argon- 38. Argon-36 has an atomic mass of 35.968 amu. Argon- 38 has an atomic mass of 37.962 amu.

a) 37.763 amu
b) 36.167 amu
c) 39.948 amu
d) 3616.74 amu

Answer 1

To calculate the average atomic mass of a sample of argon that is 90% argon-36 and 10% argon-38, multiply the percentage (expressed as a fraction) by the atomic mass of each isotope, then sum the results. The calculated average atomic mass is 36.1674 amu, matching option b) 36.167 amu.

Step-by-step explanation:

The question asks us to calculate the average atomic mass of a mixture of argon isotopes. The given sample consists of 90% argon-36 and 10% argon-38.

To find the average atomic mass, we use the formula:

average atomic mass = (fraction of isotope 1 × atomic mass of isotope 1) + (fraction of isotope 2 × atomic mass of isotope 2)

For argon-36 (mass = 35.968 amu):

0.90 × 35.968 amu = 32.3712 amu

For argon-38 (mass = 37.962 amu):

0.10 × 37.962 amu = 3.7962 amu

Adding these together gives us:

32.3712 amu + 3.7962 amu = 36.1674 amu

The average atomic mass of the mixture is 36.1674 amu, which is closest to option b) 36.167 amu.