A radium-226 sample initially contains 0.112mol. How much radium-226 is left in the sample after 6400 years. The half-life of radium-226 is 1600 years.

Answer 1

long way.
k = 0.693/t_1/2
ln(No/N) = kt
No = 0.112 mol
N = unknown
k from above.
t = 6400 years.

shorter way.
0.112*(1/2^n)
0.112*(1/2^6400/1600)
0.112*(1/2^4) = N

Answer 2

0.04 is the answer

Answer 3

The half-life of Radium -226 is 1600 years. How much Ra 226 remains in a 30.0 g sample after 6400 years?