Name: Worked example: Determining an empirical formula from combustion data | AP Chemistry | Khan Academy
Uploaded: 2020-04-06T07:49:39.000Z
Duration: 10 min 2 s
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- [Instructor] We are told that a sample of a compound

containing only carbon and hydrogen atoms

What is the empirical formula of the compound?

All right, now let's just try to make sure we understand

They say that I have some mystery compound.

so it's going to have some number of carbon,

Some number of hydrogens, I'll call that y.

We're going to put it in the presence of molecular oxygen

I'm going to end up with some carbon dioxide and some water.

this is a chemical reaction that I'm describing.

I could try to, even with the x's and y's,

The point of this video is they tell us how many grams

And so what we need to do is say, all right,

from that, we can figure out how many moles

and from that, we can figure out how many moles

and how many moles of hydrogen did we start with?

then we can come up with the empirical formula

So just to start, because I'm going to be thinking

and the mass of a mole of a molecule or an atom,

for carbon, hydrogen, and oxygen for us to work with.

So I'll get out our handy periodic table.

We can see hydrogen has an average atomic mass of 1.008.

and then last, but not least, we have oxygen

and then oxygen is at 16.00 grams per mole.

but whether we can think of that as molar mass,

how many moles of C in the product do we have?

So we can see that all of the carbon in the product

is in the carbon dioxide that's in the product,

We can think about how many moles of CO2 that is,

actually, let me just put it right over here.

So it is going to be 12.01 plus two times 16.

but now we're thinking about moles per gram,

the grams of CO2 would cancel the grams of CO2

but I care about moles of carbon in the product.

Well we know that we have one mole of carbon

Every carbon dioxide molecule has one carbon in it,

and then times one, so I don't have to do anything there.

That is equal to, I'll round it to three digits here,

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Worked example: Determining an empirical formula from combustion data | AP Chemistry | Khan Academy

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