Chemistry
posted by Nancy .
The half life of U238 is 4.5 x 10^9 yr. A sample of rock of 1.6 g produces 29 dis/sec. Assuming all radioactivity is due to U238 find percent by mass of U 238.
I have tried
ln(t)/ln(0)= kt and still cannot get the answer
What I get is
A) 4.5x10^9 x365x60x60x24=1.419x10^17 for half life
B) .693/1.419x10^17=4.883x1018
C) ln t/ln 29= (4.883x10^18)
That is the farthest I've gotten. Can someone help?

Use Nt/N0 = e^{kt}
1[yr] = a = 31557600[s]
(1/2) = e^(kh)
Where:
Half life: h= 4.5e9 * a = 1.420092E+17[s]
k = ln(0.5)/1.420092E+17
.: k = 4.8810019E18[/s]
Okay, so far. To continue...
Assume there is n atoms of U238 in the sample. t=1 second latter there is n29. (via 29 disintegrations per second)
(n29)/n = e^{kt}
1  (29/n) = e^{kt}
29/n = 1e^{kt}
n = 29/(1e^{kt})
n = 29/(1exp(4.8810019E18))
n = 5.9414031E+18[atoms]
Next: find the weight of this number.
Given:
1[mole]=6.02214129(27)E+23[atoms]
U[238] weighs 238.05078822[g/mol]
Express as a percentage of the sample weight (1.6[g]).
Respond to this Question
Similar Questions

Chemistry please help!
A Cesium 137 sample has a measured radioactivity of 50 microcuries.Cesium 137 has a halflife of 30 years. How long will it take this sample to be reduced to a residual radioactivity of 6.25 microcuries? 
Chemistry *URGENT*
URGENT help! 3. A rock sample was dated using potassium40, Neasyrenebt ubducated tgat 1/8 of the original parent isotope is left in the rock sample. How old is the rock? 
HalfLife
Uranium238 decays to Lead206. The half life of Uranium238 is 4.5 billion years. If you have a 100 g sample. How much sample will you have after 2 half lifes? 
chemistry
I have: the half life of U238 is 4.5 x 10^9 yr. A sample of rock of mass 1.6g produces 29 disintegrations per second. find percent by mass of U238 in rock. I have 4.5x 10^9x60x60x365x24=1.419x 10^17= .693/1.419 x10^17 =4.883x10^18 … 
Chemistry
I don't know if I should be posting this on a new session or just the old one; I asked it yesterday and I have not seen a reply I have: the half life of U238 is 4.5 x 10^9 yr. A sample of rock of mass 1.6g produces 29 disintegrations … 
Chemistry 1046
Geologists can estimate the age of rocks by their uranium238 content. The uranium is incorporated in the rock as it hardens and then decays with firstorder kinetics and a halflife of 4.5 billion years. A rock contains 65.7% of the … 
Chemistry
Geologists can estimate the age of rocks by their uranium238 content. The uranium is incorporated in the rock as it hardens and then decays with firstorder kinetics and a halflife of 4.5 billion years. A rock is found to contain … 
Chemistry
Pu238 is radioactive by alphadecay (halflife 87.7 y). Each decay releases 5.6 MeV of energy. Pu238 is sometimes used to power space probes. If all the decay energy can be converted to electric power, what mass of Pu238 would be … 
Chemistry (Dr.Bob222)
The halflife of P32 is 14 days. How long after a sample is delivered can a laboratory wait to use a sample in an experiment if they need at least 10 percent of the original radioactivity? 
college gen chem
An igneous rock contains a Pb−206/U−238 mass ratio of 0.367. How old is the rock?