
#1
Feb2712, 09:20 AM

P: 6

It's kind of baffling me when I'm encountering this question in this subchapter. It's just unusual. So I really need your help :D
1. The problem statement, all variables and given/known data If a rock sample was found to contain 1.16 × 10^{7} mol of argon40, how much potassium40 (t_{1/2} = 1.3 × 10^{9} yr) would also have to be present for the rock to be 1.3 × 109 years old? See assumption in Problem 14.84. And the problem 14.84 question is ... A 500 mg sample of rock was found to have 2.45 × 10^{6} mol of potassium40 (t_{1/2} = 1.3 × 109 yr) and 2.45 × 10^{6} mol of argon40. How old was the rock? (Hint: What assumption is made about the origin of the argon 40?) 2. Relevant equations k = In 2/t_{1/2} 3. The attempt at a solution I just find out that the both K and Ar in periodic table have a closely enough molecular mass, which is 40 g/mol (39,1 for K and 39,95 for Ar). But it just weird when the molecular mass is multiplied with each moles of Ar and K to find mass, because it doesn't add up for 500 mg. Also I don't have any idea what does the t_{1/2} works for. Of course we could find the rate constant from the equation before for it. 



#2
Feb2712, 09:42 AM

P: 927

What happens if you assume all the argon40 originates from the potassium40 beta minus decay? How much potassium had to be present in the rock for that much to decay?




#3
Feb2712, 10:14 AM

P: 6





#4
Feb2712, 10:55 AM

Admin
P: 22,654

Some Radiological Dating with Stoichiometry
Potassium and argon are only a small part of the sample, so their masses don't have to add to 500 mg.




#5
Feb2912, 04:01 AM

P: 6




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