A potassium-bearing mineral initially contained no argon

CHEMISTRY · Multi-part · US High School · Chemistry · Atomic Structure & Nuclear · Atomic Structure & Nuclear

Problem

A potassium-bearing mineral initially contained no argon. Today chemical analysis shows that

90\%

of the original

^{40}\text K

atoms remain undecayed. (i) What fraction of the original

^{40}\text K

atoms has decayed into

^{40}\text{Ar}

? (ii) Taking the half-life of

^{40}\text K

to be

1.25\times10^{9}\,\text{y}

, calculate the age of the mineral. (iii) How many half-lives does this age correspond to? Comment briefly on whether

^{40}\text K

is suitable for dating very old terrestrial rocks.