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AP Chemistry 3.2 Structure and Arrangement of Atoms 8 Views


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AP Chemistry 3.2 Structure and Arrangement of Atoms. What is the mole fraction of the solvent?

Language:
English Language

Transcript

00:04

Here’s your Shmoop du jour, brought to you by moles, helping you dig into chemistry the [A mole with two dinosaurs fighting]

00:09

dawn of time.

00:11

Let's burrow into the following question…

00:13

Fergie wanted to make lemonade from a mix that consisted primarily of sugar.

00:17

She prepared the lemonade solution by adding 0.50 mol of a sugar mix (solute) with 1.00

00:23

mol of water (solvent).

00:26

What is the mole fraction of the solvent?

00:29

Here are the potential answers.. lot of numbers..

00:31

In order to satisfy Fergie’s craving, we're going to have to find some black eyed peas… [Black eyed peas stirring lemonade]

00:37

But if you just don't have those on hand, math will work just fine, too.

00:41

The question is asking us what mole fraction the solvent is.

00:43

So it might be helpful to know what mole fractions and solvents are before we dive in. [Lots of moles in the ground]

00:49

Well, the question conveniently tells us the solvent is water. [A girl drinking from a bottle of water]

00:52

If only all things in the wonderful world of AP-land were so easy…

00:56

And mole fraction doesn't refer to the unfortunate outcome of moles in The Texas Chainsaw Massacre… [A theatre showing the Texas Chainsaw Massacre on screen]

01:02

What the question actually means by mole fraction is simply what fraction of the total stuff

01:08

is the particular stuff we care about.

01:10

Kind of like if we were at a buffet that only offered two options: chocolate, [People holding plates at a buffet]

01:15

or asparagus-wrapped eggplant.

01:16

So what fraction of the buffet do we care about, or, what fraction of the buffet is

01:21

chocolate?

01:22

Also, where do we find a better buffet…?

01:24

Okay, back to the question…how much total stuff do we have? [Person sitting with feet up watching hoarders on TV]

01:28

Well, we have one mole of water and half a mole of sugar, so that gives us 1.50 total

01:32

moles of things in the mixture.

01:34

Since the question conveniently told us that the water is the solvent, we know that’s [A glass filling with water]

01:39

what we need to know the fraction of.

01:40

Now comes the scary part…

01:42

We're talking math.

01:43

But don't worry, it’s not that terrifying. [A kitten sat with a calculator]

01:45

All we have to do is divide the moles of the solvent by the total moles in the mixture.

01:49

We take 1.00 moles and divide it by 1.50 moles to give a mole fraction of 0.6666666666….

01:56

and let’s just round that to 0.667.

01:58

That means the answer is B.

02:00

But just for kicks and giggles, let's check out the rest of the answers. [Guy kicks friend in his leg]

02:03

Sounds almost as fun as chowing down at the chocolate, asparagus, eggplant buffet. [Man eating at a buffet and face turns green]

02:07

Since a mole fraction is some fraction of the total, it can’t be bigger than 1, which

02:11

rules out answer A.

02:12

Answer D, 0.500, says that half of the mixture would be water, which means there would be [A glass of water and a pile of sugar]

02:17

equal amounts water and sugar.

02:18

But if we look at the amounts we're given, 1 mole is more than 0.5 moles, so the fraction

02:24

should indicate that there is more water than there is sugar.

02:28

Answer D is out.

02:29

Similarly, answer C, 0.333, says that there is less water than sugar, which is also wrong.

02:35

Which leaves us with answer B again.

02:37

Phew. [Girl standing at a lemonade stand]

02:38

Time to wash that answer down with some refreshing lemonade and….

02:41

…Great.

02:42

All we have is eggplant and asparagus. [Eggplant and asparagus appear on a table of lemonade]

02:44

Seriously people, we need a new buffet around here c'mon.

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