find the number of grams of iodine-131 remaining after 486 days if 19g of the isotope were initially present. The half life of iodine-131 is 81 days. find the number of grams of iodine?

NOTE :This is a pre-calculus question, it looked like a chemistry question, you guys probably had this question, but it just showed up on my before test review. It maybe has something to do with exponential decay or exponential growth.
Here is the question:
find the number of grams of iodine-131 remaining after 486 days if 19g of the isotope were initially present. The half life of iodine-131 is 81 days.

1 Answer
Apr 12, 2018

#0.296875# gm

Explanation:

The amount of a substance with half-life #h# remaining after #t# time periods is given by:

#Q_t = Q_0xx(1/2)^(t/h)#
Where; #Q_0# is the initial amount of the substance.

In this example, iodine-131 has a half-life of 81 days. We have an initial amount of 19 gm.

#:. Q_486 = 19 xx (1/2)^(486/81)#

#= 19 xx (1/2)^6#

#= 19 xx 1/64 = 0.296875# gm