00:01
Chapter 21.
00:02
Question to rotate.
00:03
How much time is required for a 6 .25 milligram sample of chromium to decay to 0 .75 milligram.
00:10
If it is halfe, if the halveh, uh, if the half -five is 27 .8 days.
00:16
So if they give us the half, which is, let's say this is t -half, and this is equal to 27 .8.
00:34
Now, there are two ways to solve this question.
00:37
First, you can write the first soldier half -life reaction and get the rate constant k from it and then just use the first order reaction rate law and using the k and the initial amount of the chromium and the final amount of the chromium you can always find the result or if they give the half -life then you you may think maybe what we have is after a few half lifetimes.
01:14
So let's see, we have 6 .75 milligrams and let's say this is 100%...