Chemistry
posted by Trixie T .
A radioactive sample contains 3.25 1018 atoms of a nuclide that decays at a rate of 3.4 1013 disintegrations per 26 min.
(a) What percentage of the nuclide will have decayed after 159 d?
%
(b) How many atoms of the nuclide will remain in the sample?
atoms
(c) What is the halflife of the nuclide?
days
The equations I used were
t1/2 = ln2/k to find the half life
and N'=Nekt
I used the equations above and solved for part b, the number of atoms and found this to be 2.976E18 which IS correct. I converted the 159 days into minutes, and found k by taking the rate (now in days) and dividing by the original number (N) and getting 3.836E7 for k
I then plugged this into N*ekt with t now in minutes and got my answer for part B. (2.976E18 atoms).
So my problem is with part 1 and 3....I thought it would be pretty straight forward, subtracting the remaining atoms from the original to get the amount that decayed. Then taking that amount, dividing it by the original to get the percent decayed. I keep getting 8.43% for this....but it's incorrect.
Finally for C, I thought I would just convert everything back to days, then take ln2/k (in days now) to get the half life...but I guess something is wrong here too. Can someone please explain how to do this? Thanks!

http://www.jiskha.com/display.cgi?id=1271457315
check my work.