Wednesday

October 22, 2014

October 22, 2014

Posted by **Anon** on Friday, March 5, 2010 at 4:49am.

3. A rock sample was dated using potassium-40, Neasyrenebt ubducated tgat 1/8 of the original parent isotope is left in the rock sample. How old is the rock?

5. When a sample of lava solidfied, it contained 28g of uranium-238. It that lava sample was later found to contain only 7g of uranium-238, how many years had passed since the lava solidified?

6. AFter 25 years, the number of radioactive cobalt atoms in a sample is reduced to 1/32 of the original count. What is the half-life of this isotope?

How would you find the answers to these questions?

TEll me the steps.

Thank you very much.

- Chemistry *URGENT* -
**DrBob222**, Friday, March 5, 2010 at 12:00pm#3 has so many typos I can't translate it. Please repost.

#5. ln(No/N) = kt. I don't see k listed in the problem but it can be calculated from k = 0.693/t_{1/2}. Thus, look up the half-life for U-238, substitute in the second equation to find k, then solve the first equation for t. No = 28 g. N = 7 g. The unit for t will be th same units used for the half-life.

#6. Use ln(No/N) = kt.I would make up a number (some convenient number such as 160) for No, then 1/32 x 160 will be N and you can solve for k since you are given t. Then k = 0.693/t_{1/2}and solve for t_{1/2}.

**Answer this Question**

**Related Questions**

Radioactivity - 1. A granite rock is thought to be about 2 billion years old. ...

College Geology - assume that a particular radioactive-isotope has a half-life ...

geo/science - could you please tell me if this is the correct formula for ...

earth space science - Potassium-40 has a half-life of approximately 1.25 billion...

Geology - If a rock contains an isotope with a half live of 600 million years, ...

Physics - If a sample of a radioactive isotope has a half-life of 5 year(s), how...

Geology - Hi there I'm having trouble with this study guide. Could someone ...

Calculus Help Please Urgent!!! - At time t=0, an astronaut stands on a platform ...

chemistry help! - Potassium has an atomic mass of 39.10amu. a sample of ...

Chemistry - 0.12 g of rock salt(NaCl and impurities) was dissolved in water and ...