Question 2 Silver forms ccp lattice and X-ray studies of its...

Question 2 Silver forms ccp lattice and X-ray studies of its crystals show that the edge length of its unit cell is 408.6 pm. Calculate the density of silver (Atomic mass = 107.9 u). Question 3 An element has a body-centred cubic (bcc) structure with a cell edge of 2.88Å. The density of the element is 7.2 g/cm³. How many atoms are present in 208 g of the element?

Transcript

00:05 I had started solving this problem and then i got a phone call that i had to take and i'm not going to rewrite it all again here.

00:10 So let me go through what's going on.

00:13 And in this problem, we had two things to do.

00:15 Our first thing was we were given silver, which is cubic clothes packed or face centered cubic, which i'd like to call it.

00:22 We were given an edge of 408 .6 p .meters, an edge length, an atomic mass of 107 .9 unified mass units.

00:31 We were asked to calculate the density.

00:36 Get over to my, there we go.

00:39 So the first thing i did was calculate volume.

00:42 And i converted picometers to centimeters, and i guess i should have put a centimeter right here.

00:50 So when i got done with that, this was my volume in cubic centimeters.

00:58 And of course, mass equals density times volume.

01:01 In a cubic close packed, we have four atoms per unit cell.

01:05 So now i found the mass of one atom by taking my atomic mass divided by avagadro's number, and there's my mass.

01:13 Then i took that mass.

01:16 Here's my mass from right there, times four.

01:19 That's the number of atoms in my unit cell to get my total mass.

01:23 And i divided the mass by the volume to get my density.

01:29 And there's our question one, the density of silver.

01:33 For the second problem, we were told that we had an element that is body -centered cubic, and it's got an edge length of 2 .8, 2 .88 angstroms and a density of 7 .2 grams per centimeter cubed.

01:49 We were asked how many atoms are present in 208 grams of this sample? how many atoms are present in 2 .8 grams of this sample? okay.

02:04 How many atoms are present? and i did.

02:08 My first thing again is i found my volume.

02:11 This time there are one times 10 to the 10th and i kept writing the wrong number here.

02:16 Here repeatedly.

02:18 There is, oh darn it.

02:23 There's one times 10 to the 10th, inkstroms, and this should be angstroms and centimeters.

02:33 Let me write this a little bit nicer here.

02:37 That's ink ,rums and centimeters...

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