00:01
Well, let's see if i get this problem.
00:02
We're told at 25 degrees c.
00:04
The density of k is 0 .56 grams per cubic centimeter.
00:19
The unit cell edge length is equal to, let me get over here, 5 .33 angstroms.
00:50
We're asked to find the number of formula units in a unit cell of k.
01:02
The molar mass is given as 39 grams per mole.
01:11
So, okay, first we're going to get the average mass of one atom.
01:26
In order to do that, i'm going to take 39 grams per mole and i'm going to multiply that by 6 .022 times 10 to the 23rd atoms per mole.
01:55
This will give me 39 divided by 6 .022.
02:02
We'll give me 6.
02:03
I'll round later times 4 .76.
02:06
Times 10 to the minus 23rd grams per atom.
02:16
That's step a.
02:18
Step b.
02:21
I'm going to figure out the atoms in one cubic centimeter.
02:34
I'm going to do that by taking my density 0 .56 grams per cubic centimeter times 6 .477 times 6 .470.
03:02
76 times 10 to the minus 23 grams per atom.
03:12
And this will equal 0 .56 divided by second answer will give me 8 .47 times 10 to the 22nd unit cells.
03:43
So that'll be how many unit cells? i'm not talking to you.
03:51
Well, that's good at least.
03:54
Okay, sorry about that.
03:57
I got interrupted there for a moment, but that's okay.
04:00
No big deal.
04:01
C, the number of unit cells.
04:08
Now, let's do the volume.
04:17
That's the number of atoms in one unit cell.
04:21
This was incorrectly marked.
04:25
Number of atoms.
04:29
Let me do this again...