Posted by **Angie** on Wednesday, April 15, 2009 at 4:28pm.

Cesium-137 has a half-life of 30 years. Suppose a lab stored a 30-mCi sample n 1973. How much will be left in 2063?

- Chemistry/math -
**DrBob222**, Wednesday, April 15, 2009 at 5:45pm
Use the half life to calculate the k in

k = 0.693/(t1/2).

Then use k in the following equation.

ln(Co/C) = kt

Co = 30 mCi

Solve for C. The answer will be in mCi.

k = from above

t = years from dates listed.

Post your work if you get stuck.

- Chemistry/math -
**Angie**, Wednesday, April 15, 2009 at 5:52pm
what does k stand for?

- Chemistry/math -
**DrBob222**, Wednesday, April 15, 2009 at 6:01pm
k is the proportionality constant for the equation:

ln(Co/C) = kt and it is evaluated from k = 0.693/t(1/2). In this case, its

k=0.693/30 years = ??

- Chemistry/math -
**Angie**, Wednesday, April 15, 2009 at 6:36pm
0.0231?

- Chemistry/math -
**DrBob222**, Wednesday, April 15, 2009 at 8:28pm
Yes, k = 0.0231 years^-1. Now put that into the ln formula I provided and solve for C following the instructions I gave you.

- Chemistry/math -
**Angie**, Wednesday, April 15, 2009 at 9:37pm
why is it to the -1?

- Chemistry/math -
**DrBob222**, Wednesday, April 15, 2009 at 11:34pm
Are you putting me on?

1/x = x^-1.

so 0.693/30 = 0.0231 years^-1. It's just a unit and the -1 means years is in the denominator. It's the same thing as saying wavenumber = 1/5 cm = 0.2 cm^-1 or in words it is 0.2 reciprocal centimeters.

- Chemistry/math -
**Angie**, Thursday, April 16, 2009 at 1:33pm
ok thanks

## Answer This Question

## Related Questions

- algebra - Suppose a sample of Cesium-137 with initial mass of 200 grams decays ...
- word problem - The half life of cesium-137 is 30 years. Suppose we have a 10-g ...
- Chemistry please help! - A Cesium 137 sample has a measured radioactivity of 50 ...
- chem - Cesium-137 has a half life of 30.0 years. If initially there are 8.0 kg ...
- math - 5. Cesium-137 is a radioactive isotope. The following formula represents ...
- Chemistry - The cesium-131 nuclide has a half life of 30 years. After 90 years, ...
- chem - A typical dose of a radioactive sample is 27.0 mCi. How long does it take...
- Calculuc - How do you set up this problem? The decay constant for the ...
- Chem 3A - please help me with this chemistry problem. Half-Life A radium-226 ...
- chemistry - Strontium-90 has half-life of 28 years. if a 1.00-mg sample was ...

More Related Questions