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August 30, 2014

August 30, 2014

Posted by **Anon** on Friday, November 23, 2012 at 9:04pm.

What is the molecular formula of the compound?

What is the geometry shape around each carbon atom?

Polar or Nonpolar?

- Chemistry -
**DrBob222**, Friday, November 23, 2012 at 9:39pmUse PV = nRT and solve for n = numbre of mols. Substitute into n = grams/molar mass. You know mols and grams, solve fo rmolar mass. Use that number later.

Take a 100 g sample which gives you

38.734 g C and 61.266 g F. Convert to mols.

38.734/12 = ?

61.266/19 = ?

Find the ratio of C to F with the smallest number being 1.00. The easy way to do that is to divide the smaller number by itself; then divide the other number by the same small number. That gives you the empirical formula.

Calculate the mass of the empirical formula and substitute into

empirical formula x ?number = molar mass from above and round ?number to a whole number.

The molecular formula is (CxHy)_{?}

Post your work if you get stuck.

- Chemistry -
**Anon**, Friday, November 23, 2012 at 9:53pmFor n I got 26.18 mols. For the mass I got 31 because it was CF.

- Chemistry -
**DrBob222**, Friday, November 23, 2012 at 10:00pm26.18 is not right. CF is the empirical formula. The empirical mass is not 31. You need the molar mass from mols and grams.

- Chemistry -
**Anon**, Friday, November 23, 2012 at 10:28pmThe moles of C is 3.227. The moles of F is 3.224. Therefore the empirical formula is CF. How would I find the empirical mass? Your explanation is confusing.

- Chemistry -
**DrBob222**, Saturday, November 24, 2012 at 12:19amYes, I said the empirical formula of CF is correct. My error for empirical mass; it is 12 + 19 = 31 as you noted.

Here is how you do the molar mass.

PV = nRT

P = 1.10 atm

V = 10.0 mL = 0.0100 L

n = solve for this

R = 0.08206 L*atm/mol*K

T = 288.5 K.

Solve for n = about 5E-4 but that is just a close estimate.

Then n = grams/molar mass and

about 5E-4 = 0.02882/molar mass.

Solve for molar mass which is approximately 60.

The molecular formula then is

empirical formula x ? number = molar mass

31 x ? = 60

? = about 2 when rounded to a whole number; theefore, the molecular formula is

(empirical formula)_{2}or

C2F2

You should go through and confirm those numbers since they are just estimates on my part.

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