chemistry...?

Question

If 0.0463 g of a radioisotope remained after five half-lives, then the original mass was _____ g.

when answering would you mind telling me how you came up with your answer please and thankyou to all who answer!

Answer 1

Each time period you get half of what you had. Going backwards, you would have twice as much. So after one 1/2 life backwards, you have .0926. Then .1852, .3704, .7408, and finally 1.4816 after 5 half lives.

Answer 2

M =M(0)*2^(-t/T)

where M mass, M(0) mass at time 0, T half-life

here t/T = 5

M = M(0)*2^(-5)

M(0) = M*2^5= 32 M= 0.0463*32 =1.4816g