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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: SilentSundown on November 17, 2014, 04:55:35 PM

Title: Hydroxyl problem
Post by: SilentSundown on November 17, 2014, 04:55:35 PM

So, I've been trying to solve this problem for a while now and I just can't figure out what I'm doing wrong or what I'm missing...
It says: 3g of a hydroxy compound reacts with acetic anhydride used in excess. The reaction product has 7.25g. What alcohol is it?

I would appreciate your help a lot.

Title: Re: Hydroxyl problem
Post by: Borek on November 17, 2014, 05:30:03 PM

Show what you tried so far and we will start from there.

Title: Re: Hydroxyl problem
Post by: SilentSundown on November 17, 2014, 11:45:53 PM

I wrote the ecuation like this:
 
R-(OH)n + n(CH₃CO)₂O ---> nCH3-COOH + R-(OCO-CH3)n

mCH3-COOH = (60x3)n/(R+17n) 
mR-(OCO-CH3)n = [3(59n+R)]/(R+17n)

(I got this from ecuation)

Then I summed them up , then tried to give the R different values to see if n is a whole number.

Oh, the choices I have to make are the alcohols formed from penthane ..

Title: Re: Hydroxyl problem
Post by: kriggy on November 18, 2014, 01:36:06 AM

And what was the result? ;)
Consider this:
adding acetate to the molecule of alcohol increases the yield by 4,25g. If you know mollar mass of acetate can you calculate amount of moles of acetate in your product? You can then calculate amount of moles of your alcohol and its mollar mass. From molar mas it should  be easy to deduce which alcohol it is.
If you have choices, than it should be even easier.

Title: Re: Hydroxyl problem
Post by: SilentSundown on November 18, 2014, 02:30:30 AM

The answer is C5H12O5, but i don.t know how to obtain it.. can you be more specific? What is the formula for yield? I am not english and i don.t know what the formula means..

Title: Re: Hydroxyl problem
Post by: Borek on November 18, 2014, 03:23:43 AM

By "yield" kriggy means mass of the product. Just follow the stoichiometry.