Potassium-40 is a radioactive isotope of potassium, which is a common element in
ID: 1038065 • Letter: P
Question
Potassium-40 is a radioactive isotope of potassium, which is a common element in crustal minerals. A common K-containing mineral is orthoclase feldspar, with the formula KAlSi3O8.
What is the mass fraction of K in orthoclase feldspar?
The K-40 isotope comprises 0.0118% of the potassium found in natural samples. How many atoms of K-40 are there in one mole of orthoclase feldspar?
This many atoms of K-40 would result in how many disintegrations per minute? (Assume k for the decay reaction = 1.055 x 10-15 min-1.)
Explanation / Answer
Name of the mineral - Orthoclase feldspar
Molecular Formula KAISi3O8
Mass of each component given =
K 40
AI 27
Si 28, So 3 *28 = 84
O 16, So 8* 16 = 128
Total Mass = 279 u
Mass Fraction of K = 40 / 279
=0.14336
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