Question

Potassium has an atomic mass of 39.10amu. a sample of potassium is made up of isotopes potassium-39 (mass=38.964) and potassium-41(mass =40.962 amu). What percentage of the potassium sample is potassium-39? what percent of the sample is potassium-41?

Answer 1

For a sample of K, with x grams of ³⁹K and y grams of ⁴¹K the total mass will be

38.964x + 40.962y

Assuming a sample of 100g, we have

38.964x + 40.962(100-x) = 39.10(100)
x = 93.193

³⁹K is 93.193%
⁴¹K = 6.807%

check:

38.964*.93193 + 40.962*.06807 = 39.10