00:02
Hi there.
00:03
In this question, we are working with average atomic mass.
00:09
And average atomic mass is actually a weighted average.
00:14
In other words, it's not just a straight, add them together and divide by two idea.
00:19
It's a weighted average.
00:20
And you might have the most experience with weighted averages in the calculation of grades.
00:26
Perhaps your teacher counts homework as 20%, quizzes is 30%, and tests as 50%.
00:31
Well, then to calculate your grade, you need to take.
00:34
Those percentages times the average for each category and add those products together.
00:40
So the same thing is true when calculating an average atomic mass.
00:46
We have to take the product for each isotope, its abundance times mass.
00:52
We take the abundance, percent abundance, times the mass for each isotope, and add these products together to get the average atomic mass.
01:15
That's how you would do a weighted average.
01:17
So that means that our average atomic mass here, which we are given as being 192 .217 amu is going to be the result of adding together the abundance times the mass for each of these isotopes.
01:40
All right, well, we are given information about arridium 193.
01:46
We know it is 62 .7.
01:50
70 % iridium 193.
01:57
And the mass of that is 192 .963.
02:14
Okay, so we need to multiply these together, and then we need to add it to the percent abundance times the mass for the eridium 191.
02:23
Well, we're not told either of these.
02:26
Based upon percent abundant, or looking at the percent abundance, we know there's only two isotopes.
02:32
So that means the total percent has to add to 100...