21. Nuclear Chemistry

The half-life of arsenic-74 is about 18 days. If a sample initially contains 5.13 x 10⁴ mg arsenic-74, what mass (in mg) would be left after 80 days?

What percentage of carbon – 14 ( t_1/2 = 5715 years) remains in a sample estimated to be 18,315 years old? 

What fraction of a reactant has been consumed after 4 half-lives in a first-order reaction?

What is the rate constant of a first-order reaction when 20.0% of a reactant remains after 30.0 s?

A fossil is found to have a ¹⁴C level of 76.0% compared to living organisms. How old is the fossil?

A moon rock collected by the Apollo mission is estimated to be 3.80 billion years old by uranium/lead dating. Assuming that the rock did not contain any lead when it was formed, what is the current mass of 206 Pb in the rock, given that it currently contains 1.180 g of 238 u? The half-life of ²³⁸U is 4.47×10⁹ years.

A rock from Australia contains 0.438 g of Pb-206 for every 1.00 g of U-238. Assuming that the rock did not contain any Pb-206 at the time of its formation, how old is the rock?