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Topic: Percent yield calculations  (Read 23684 times)

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Offline christina

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Percent yield calculations
« on: November 25, 2007, 02:53:16 PM »
rxn:

I oxidized the borneol to get camphor then reduced that to get isoborneol

borneol + glacial acetic acid + 6% sodium hypochlorite + acetone => camphor

camphor + sodium borohydride + methanol => isoborneol

I need to calculate the percent yield of the camphor and also of the isoborneol.

I don't know the ratio or the limiting reagent though for the first rxn or second reaction.
:)

Offline ARGOS++

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Re: Percent yield calculations
« Reply #1 on: November 25, 2007, 05:39:57 PM »

Dear ~Christina~;

What has Mr. Borek answered to a quite similar Question:
Quote
Most likely you should start with balanced reaction equation and molar masses of all compounds mentioned.

It is very wisely, because it’s the real starting point of all.

Good Luck!
                   ARGOS++

Offline christina

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Re: Percent yield calculations
« Reply #2 on: November 25, 2007, 07:06:57 PM »
ok but I was wondering about it since I'm not sure how do I incorperate the glacial acetic acid into that. What would happen in the rxn that needs the acid?
:)

Offline enahs

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Re: Percent yield calculations
« Reply #3 on: November 25, 2007, 07:47:51 PM »
The glacial acetic acid is irrelevant unless it was your limiting reagent?

You are just interested in, theoretically how much isoborneol you can get from borneol. This requires balanced equation(s) and knowing how much you started with.





Offline RBF

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Re: Percent yield calculations
« Reply #4 on: November 25, 2007, 08:05:36 PM »
I believe the general equation for the oxidation is:
R2CHOH + HClO==>R2C=O +H2O +HCl

I believe the acetic acid converts the hypochlorite to hypochlorous acid, which is the oxidizing agent.  I assume that acetone is the solvent.  Check the amount of hypochlorite to determine whether it is the limiting reagent .  Once you determine the limiting reagent, proceed as usual.

Offline Jolofgirl

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Re: Percent yield calculations
« Reply #5 on: November 25, 2007, 10:20:30 PM »
I'm doing a similar reaction . I think that you should only worry about the initial mass of your isoborneol because the other ones are irrelevant. I think the theoretical moles of camphor is the same as isoborneol, then u multiply that by the molar mass, and you find your theoretical mass. the rest I think you know how to do..
Not sure a 100% but hey.. trying to help
Good luck

Offline RBF

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Re: Percent yield calculations
« Reply #6 on: November 25, 2007, 11:13:22 PM »
If you add insufficient hypochlorite to complete the reaction, it will not be irrelevant to your result.  It is a good idea to verify that, in fact, the inorganic reagent is added in sufficient amount to complete the reaction.  If the procedure came from a laboratory exercise, your assumption may well be true (I suspect it is in this case).  However, a student may need to perform a similar reaction down the road, and the ability to calculate the necessary amount of reagent will be important.

Offline christina

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Re: Percent yield calculations
« Reply #7 on: November 28, 2007, 05:37:19 AM »
Thank you RBF, the rxn did go to completion and thus I just used the borneol
as the limiting reagent in the first rxn and the camphor as the limiting reagent in the second rxn to get isoborneol.
It was verified in the lab through IR that all the borneol in the first rxn where I had to use acetic acid was converted to camphor.

The 2nd rxn's theoretical moles of camphor I do not think are the same as the isoborneol since the ratio for the isoborneol I think when I looked something up said that it was a 1/4 ratio of it to sodium borhohydride thus not 1:1 since the sodium borohydride has 4 hydrogens.
:)

Offline RBF

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Re: Percent yield calculations
« Reply #8 on: November 28, 2007, 03:05:19 PM »
The 4:1 ratio you mention is the ratio of camphor to sodium borohydride, assuming that all four of the 'hydride ions' are available for reaction.  This is not directly related to the ratio of camphor reacted to isoborneol produced, which is the issue you need to resolve in calculating the percent yield. ( I am assuming that sodium borohydride is not the limiting reagent here)

Do any of the carbon atoms from isoborneol come from anywhere else but camphor?  The answer to that should tell you what the mole to mole ratio is between the two compounds.

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