Question

A volcanic eruption melts a large area of rock, and all gases are expelled. After cooling, "Ar (atomic number 18) accumulates from the ongoing decay of 40K (atomic number 19) in the rock (4112 = 1.25 x 10°yr). When a piece of rock is analyzed, it is found to contain 1.37 mmol of "'K and 1.06 mmol of 40 Ar. How long ago did the rock cool? Enter your answer in scientific notation. X 10 (select) years

Answer 1

Given, ty2= 1.25 x 10 ур 0.693 0.693 .: KE trz 1,258109 - 5.544x10-10 yn = 1 The decay reaction is - 40 igk Ano 18 Time required foro cooling of rock 40 t = In (1+ A) K This can also be An explain as- 1 greatom of 400 produce 1g-atom of to :. Initial amount of 10 K = (1.37 + 40 16 8 x 1.06)= Time hequired for decay of 2.43 mmet u dok to 2. 43 mmol 1.37 mmol Bed t= 14 lu (HS en 2.93 5. 544010 1.37 t = 1.033x10 9