# chemistry

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How long will it take for the 100mg of cesium-137 to decay to 6.25mg(1/16 the original amount)?

• chemistry -

2n = 16
Solve for n = number of half lives.

• chemistry -

still i can't understand it

• chemistry -

Do you have the half-life given in the problem or are you allowed to look it up? If so there is an easier way to set it up.
To solve 2n = 16, take the log of both sides.
log 2n = log 16
n*log 2 = log 16
n*0.301 = 1.2 etc.

There is another way. Remember that half-life means the time it takes for 1/2 the material to disappear. So make a table like this. The periods are used for spacing.
amount......# half-lives
100 mg.........0
50 mg..........1
25 mg..........2
12.5 mg........3
6.25 mg........4
So whatever the half-life is, multiply that by 4 and you will have the time it takes to go through 4 half-lives.

• chemistry -

thanks alot , this answer really helped me to understand this question

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