Caproic Acid Question

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Vincent Chiang 1L
Posts: 54
Joined: Fri Sep 29, 2017 7:05 am

Caproic Acid Question

Postby Vincent Chiang 1L » Thu Oct 05, 2017 7:52 pm

Caproic acid is composed of C, H, and O. 0.225 g of this sample is combusted.
0.512 g of CO2 is produced.
0.209 g of H2O is produced.
What is the empirical formula?

This question was given during discussion section. I found how many moles of each product were produced (both were 0.0116 mol), but I don't know what to do from there... help please? Thanks in advance.

Abigail Yap 2K
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

Re: Caproic Acid Question

Postby Abigail Yap 2K » Thu Oct 05, 2017 9:10 pm

I converted the 0.512g of CO2 to moles of CO2, converted the moles of CO2 to moles of C, and the moles of C to grams of C. I then calculated the mass of H by going through these same steps for the H2O. This gave me 0.140g C and 0.0234g H. I then calculated for the mass of O by subtracting the masses of C and H from the starting mass of the caproic acid:

0.225g acid - 0.140g C - 0.0234g H = 0.0616g O

I then converted these masses to moles: 0.0117 mol C, 0.00385 mol O, and 0.0232 mol H. I divided each of these values by 0.00385 and got a ratio of 3 mol C: 6 mol H: 1 mol O. The empirical formula for caproic acid is C3H6O. (The molecular formula is twice as large, C6H12O2).

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