Question

You have found a mysterious substance that appears to be radioactive. You take a sample to a nuclear chemist who measures out 100 g. of the substance. Thirty hours later, the chemist tests the sample and finds that 6.25 grams of the sample remains radioactive. What is the half-life of the sample?
Select one:
a. 4 hours
b. 7.5 hours
c. 15 hours
d. 30 hours

Answer 1

This is a first order decay problem. Do you know the concentration - time equation for this type of process?

Answer 2

i dont think so

Answer 3

Perhaps you have not seen it yet...ok another way to do this is to start with 100 g of sample and reduce it by a factor of two each time until you get to 6.25 g...Go ahead

Answer 4

what

Answer 5

you are starting with 100 grams of sample agreed?

Answer 6

yes

Answer 7

ok, now if that sample decays by one half the 100 grams becomes what?

Answer 8

50

Answer 9

great...now keep going, dividing it by two each time until you get to 6.25

Answer 10

ok

Answer 11

Once you have done that, count how many times it divided in half to go from 100 to 6.25

Answer 12

i cant do that in my head