Question

Technetium-99 is a radioisotope used to assess heart damage. Its half-life is 6.0 h. How much of a 1.0 g sample of technetium-99 will be left after 30 h?

The answer is 31.25 mg, but how do you do it?

Answer 1

t/2 = 6h --> 30 h/6h = 5 --> 5t/2
1t/2 = 0,5 g
2t/2 = 0,25 g
3t/2 = 0,125 g
4t/2 = 0,0625 g
5t/2 = 0,03125 g ---> 31,25 mg

Answer 2

Oh ok. But I don't get how you get that answer though. is it because you that the 1/2 ^5 and multiplying it by 100%??

Answer 3

ok so its like this, you have half life of 6 h it means that in 6 hours 1 g sample will reduce its mass by half so you have 0,5 g -> that is t/2, and in another 6 hours it reduces its mass in half so it is 0,25 g -> that is 2*t/2 and in another 6 hours it reduces its mass in half so it is 0,125 g -> that is 3*t/2 and so on... do you get it now?

Answer 4

oh okay. make sense. so then do i still multiply by 100?

Answer 5

i dont get what you need to multiply with 100% ?
you get concrete value which is 31,25mg....

Answer 6

i dont know. i'm was just referring to the book.

Answer 7

but nevermind. i understand how it is 31.25 now

Answer 8

you can now calculate what percentage you have by:
0,03125/1= 0,03125 * 100 % = 3,125 %

Answer 9

oh okay. thank you. i understand it