00:04
Okay, so for this question, this is going to be a series or a couple of different dimensional analysis problems.
00:16
And so whenever we're doing dimensional analysis, i like to have my gram formula masses available for my substances if they are given in grams.
00:28
And for the first one, we are going to l .i.
00:31
Plus ions.
00:35
Sorry about that.
00:36
And for the second one, we're taking that same amount, and we're going to grams of oxygen.
00:45
Okay? so i'm just rewriting, so i have more space.
00:49
So for the first one, whenever we're doing dimensional analysis, we always want to multiply by a fraction where the numerator and the denominator are equal to each other.
01:03
Those things that we multiply by will then have a value of one because if the numerator and the denominator equal each other that's going to be equal to one so the other piece of that is that this fraction that i multiply by has to have the unit we're trying to get rid of in the bottom and the unit we want to get into in the top so i happen to to know that to go from grams to anything, i'm usually going to have to go to moles.
01:42
Oops.
01:43
So i'm going to multiply by one mole over the gram formula mass.
01:49
Once i am in moles, i can say that there are three l -i -plus for every one, l -i -3, p -o -4.
02:01
And i can also then say that there are 6 .022 times 10 to the 23rd ions per mole.
02:19
And when we cancel everything out, by canceling out units there in the top and the bottom, my final unit comes out to lithium ions.
02:29
And then the last step is just putting this into the, calculator.
02:36
So we just multiply and divide the way that we would normally multiply and divide fractions.
02:46
Multiply across the top, divide by what's on the bottom, and i'm going to write down my answer, but then i'm going to check my math again.
03:00
So that's what i get, but i do always double check my math, and by writing it out like this, i can always make sure that i can always make sure that i can reproduce and put this right back in the calculator.
03:16
So this is my answer for ions of lithium.
03:22
So then when we want to take the same value and instead of getting to ions of lithium, we want to get to grams of oxygen, we can actually take a little bit of a shortcut here.
03:39
Because i know that there are four oxygens per formula unit, i can put the main...