Question

I need some help figuring out where I'm going wrong in calculation the questions is....The isotope^17f has 65s half life. If you start with a 15g sample of ^17f, after 32.5 s what is the remaining amount?

Answer 1

So I know that N(t)/No=e
(-0.693)32.5/65 but my answer is -0.3465
The answer is given as 0.707158819 please tell me what I've done wrong

Answer 2

you there?

Answer 3

Hi yes can u see what I did wrong

Answer 4

yep

Answer 5

\[\huge N(t) = N _{0}*(\frac{ 1 }{2 })^{\frac{ t }{ 65 }}\]

Answer 6

Ohh thankyou

Answer 7

if you want to do it in terms of 'e' :
\[N(t) = Ne ^{rt}\]
\[\frac{ 1 }{ 2} = e ^{r65}\]
\[\ln \frac{ 1 }{ 2} = r65\]
\[\frac{ 1 }{ 65 } \ln \frac{ 1 }{ 2} = r\]

Answer 8

r= -.010664

Answer 9

either way you get 15g*.70710678...

Answer 10

I don't know what I'm doing wrong but I can not get the 0.707158819

Answer 11

0.707158819*No

Answer 12

answer isn't .7071588 grams...

Answer 13

The rest of the sum I get but I can't get the initial 0.707158819 to finish the rest of the sum

Answer 14

this is less than a half-life, so the sample is even going to reach half it's original mass...

Answer 15

sum?

Answer 16

just plug 32.5 in for t

Answer 17

32.5/65 = 1/2
(1/2)^(1/2) =....?

Answer 18

Bugger me that was easier than I thought thank you
Now it's just. 0.707158819*15*10^-3kg, awesome