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March 31, 2015

March 31, 2015

Posted by **Trixie** on Friday, April 16, 2010 at 6:35pm.

I listed below already about where I am confused....I have been doing these problems by converting the t1/2 into minutes and plugging everything in to N=Ne^-kt....but I think I am confusing some variables because my answers are a bit off... Same applies for Q2.

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 half-life of the nuclide?

days

I don't need the answers handed to me...I just want to know how to do it. As before, I listed my work already....I don't know if I am making mistakes in converting or if I need to use N=Ne^-kt in a different way than I already described. Thanks for the help...

- Chemistry -
**Trixie**, Friday, April 16, 2010 at 6:43pmI figured out the first one...still struggling with the 2nd...

- Chemistry -
**bobpursley**, Friday, April 16, 2010 at 8:58pmAmountleft= Originalamount*e^-kt

-Rate=-k*original amount*e^-kt

3.4E13/26=3.25E18(k)e^k0

k= 4.023E-7 /min or 5.74E-4/day

amount left/original amount= e^-kt

= e^(-5.74E-4 *159.21E-2)

fraction left=9.21E-1=.921

fraction decayed=.079

percent decayed=7.9

halflife:

5.74E-4= ln2/thalflife

thalfflife= 1207 days

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