00:01
Okay, so the first thing that we have to find out is the number of carbon 12 initially.
00:08
So number of carbon 12 is equal to initial mass, which is 85 grams, mass of the sample, over molar mass, the atomic number 12 grams per mole.
00:23
That's 12 times the avogadro's number, which is 6 .02 times 10 to the 23.
00:31
Atoms per mole.
00:35
So this gives you a number, initial number of carbon 12 of 4 .264 times 10 to the 24 atoms.
00:45
And we're told that the number of carbon 14 nuclei initially is this number times 10 to the times 1 .3 times 10 to the negative 12.
01:02
Small proportion, a very small fraction of it, which is 5 .54 times 10 to the 12 atoms.
01:12
And so let's call this r not, initial activity, r not.
01:18
And so what we want to do now is we want to set, we want to use this equation, activity r at time t is r0 times e to the minus lambda t.
01:28
And so t is what we want and t will be log of r over r not times minus 1 over lambda and so lambda is log 2 over t half half life so this will be half life of the log 2 and right so log of r over r not let's tackle that first.
02:06
R is given as seven decays per...