# Chemistry

For my homework the question is...
What is the half life of polonium 214 if a 1 gram sample decays to 31.25mg after 820 seconds? Im not sure how you arrive at the answer, my friend says the answer is 5 but were not sure how to do it..thanks for any help u may have

ln(No/N)= kt
No = 1 gram
N = 0.03215 g
t = 820 seconds.
solve for k. THEN
k=0.693/t1/2

.03125g=1g * e^(-.692*820sec/thl)

where thl is halflife time.

thl*ln .03125 = -.692*820

thl= -.692*820/ln.03125

Check you friend:
1g
1/2g
1/4 g
1/8g
1/16g
1/32g=.0312sec
So you friend is right, it takes 5 half lives, or 820/5 seconds. Check that with the answer above.

Your friend is correct that it goes through 5 half-lives BUT the question is what is the half-life, not how many half-lives it goes through.

My equation or the one Bob Pursley gave you will give you t1/2

1. 👍
2. 👎
3. 👁

## Similar Questions

1. ### math

An element has a half-life of 30 years. If 1.0 mg of this element decays over a period of 90 years, how many mg of this element would remain? Begin amount is 1.0 elapsed time is 90y half life 30 years n=9/30 n=3 90/2^2 90/8 =

2. ### Gen Chem

Neptunium-239 has a half-life of 2.35 days. How many days must elapse for a sample of 239-Np to decay to 1.00% of its original quantity? I got: close to 15 days. Is this right? I figured that about 1% of the original quantity

3. ### Chem Class

The rate constant of a first-order process that has a half-life of 225 s is ?????? s-1. ok so i divided half life of 1st order= 0.693/K k i put 225 and i got 3.08 x 10^-3 is that right?

4. ### Chemistry

Which radioactive sample would contain the greatest remaining mass of the radioactive isotope after 10 years? A. 2.0 grams of 198 Au B. 2.0 grams of 42 K C. 4.0 grams of 32 P D. 4.0 grams of 60 Co By the way the numbers next to

1. ### college math

a medical institution request 1 gram of bismuth-214 which has a half life of 20 min. How many grams of bismuth-214 must be prepared if the shipping time is 2 hours.

2. ### physics

How long will it take a sample of polonium-210 with a half-life of 140 days to decay to one-sixty-fourth of its original strength?

3. ### Calculus

The radioactive element polonium decays according to the law given below where Q0 is the initial amount and the time t is measured in days. Q(t) = Q0 ยท 2-(t/140) If the amount of polonium left after 700 days is 45 mg, what was

4. ### Physics

Gold-198 with a half life of 2.6 days is used to diagnose and treat liver disease. Write a half life decay equation that relates the mass of au-198 remaining to time in days. What percentage of a sample of Au-198 would reamin

1. ### chemistry

If there are 80 milligrams of a radioactive element decays to 10 milligrams in 30 minutes then what is the elements half life in minutes? Ok i narrowed it down to either 10 or 30...but im rly confused so if u could help it wuld be

2. ### Science

An element has a half-life of 30 years. If 1.0 mg of this element decays over a period of 90 years, how many mg of this element would remain? Begin amount is 1.0 elapsed time is 90y half life 30 years n=9/30 n=3 90/2^2 90/8 =

3. ### Chemistry

I've figured out most of it. I'm not sure how to find the percentage ofd the isotope. Define the half life. The half-life of a radioisotope is found to be 4.55 minutes. If the decay follows first order kinetics, what percentage of

4. ### sciencemath

Suppose a laboratory has a 31 g sample of polonium-210. The half-life of polonium-210 is about 138 days. How many half-lives of polonium-210 occur in 966 days? How much polonium is in the sample 966 days later?