00:01
Hi there.
00:02
In this compound, we are tasked with finding the identity of the metal in the compound mcl2 .2h2.
00:15
In other words, it is a hydrate and has two water molecules associated with each formula unit of the mcl2.
00:25
So to find, so to determine actually what the metal is, we need to find its molar mass.
00:33
If we can find it, it's molar mass, then we can look on the periodic table and figure out which element it is.
00:38
So remember, molar mass is grams per mole.
00:42
So we need to determine the grams of m that we have and the moles of m that we have.
00:52
If we can do that, then we can figure out its molar mass and determine what it is.
00:58
So we are told that we have, after we drive off the water, we have 2 .56 ,000.
01:09
131 grams of the anhydrous compound.
01:15
In other words, just the mcl2 without the water.
01:18
With the water, the mass was 3 .00450 grams.
01:25
That means if we take the difference here, the total mass at the beginning, and subtract the mass after the water has been evaporated, we should have the mass of the water.
01:38
So let's do that.
01:39
So i'm just subtracting here.
01:43
I'm taking the mass of the entire sample, subtracting the mass of the anhydrate.
01:51
That means the compound with the water removed.
01:56
And the difference should give me the mass of the water.
01:59
So that would be 0 .4439 grams of the water.
02:08
So the water portion of this molecule is 0 .44319 of this compound.
02:17
All right.
02:21
So i have a lot of information here.
02:24
We still don't have mass of the metal.
02:26
We don't have the moles of metal.
02:28
But let's think about what we can do at this point.
02:32
Since we know the mass of the water, we can determine the moles of the water.
02:37
So let's do a little bit of work here.
02:43
319 grams of h20.
02:50
And the molar mass of water is 18 .02.
02:53
So i want to convert this to moles.
02:56
There are 18 .02 grams of water.
03:00
In this formula, if we look at this formula, we see that there are two water molecules for every m.
03:14
So there'll be two moles of h2o for every one mole of the metal.
03:24
Because looking at the formula, there's one m, there's two cls, and there's two h2os.
03:28
So two moles of h2o will give us one mole of m.
03:33
So this allows us to calculate the moles of m...