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Please help with calculating limiting reagent?


PistolSlap

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I did an experiment in which I added 0.2116 mols acetic anhydride to 0.0222 mols glucose to form 0.0178 mols glucose pentaacetate.

I am attempting to calculate the limiting reagent, but I can't balance the equation properly!
What I get is:
15 C4H6O3 + -2 C6H12O6 = 3 C16H22O11

How am I supposed to calculate a limiting reagent with negative numbers? confused.gif

Thanks!

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You can't calculate the limiting reagent with negative numbers in the equation.

But then again, how could you have negative numbers there in the first place?

I grant you that the arithmetic works- but what's the physical meaning of minus 2 glucose molecules?

You might find the name of the product to be something of a hint when balancing this.

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You can't calculate the limiting reagent with negative numbers in the equation.

But then again, how could you have negative numbers there in the first place?

I grant you that the arithmetic works- but what's the physical meaning of minus 2 glucose molecules?

You might find the name of the product to be something of a hint when balancing this.

 

i dont get it!!! i got the negative numbers by inputting the formula into a equation balancer. what it told me is that the negative number means that value is on the wrong side and the equation actually goes: "acetic anhydride = glucose + glucose pentaacetate" which i have no idea what that means or how do i calculate a limiting reagent from the two chemicals I added together to get glucose pentaacetate?

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Perhaps glucose pentaacetate isn the only product that forms. This reaction is called a condensation reaction. Perhaps you have no idea what you were doing. You might want to figure that out first.

Edited by Fuzzwood
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i dont get it!!! i got the negative numbers by inputting the formula into a equation balancer.

 

Apparently you don't understand how Universe works.

You have f.e. 2 Hydrogens and 1 Oxygen on left side of equation, then they join/react, and there is created H2O as product.

Quantity of atoms must match! Otherwise it would be like creating stuff that was not there!

How could be negative quantity of some atoms?!

I'm intrigued by the coincidence that the "reaction " can be balanced that way with a negative amount of stuff.

 

He used some broken software "i got the negative numbers by inputting the formula into a equation balancer."..

Its programmer didn't do proper job at idiot-proofness and allowed negative numbers to be used..

Edited by Sensei
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It's not a matter of how the universe works or even bad software.

It's the wrong equation he's balancing, because it doesn't include the other product

 

+1, John.

 

I can't see how someone can have got this far in organic (or any other sort) of chemistry and be unable to balance a reaction equation.

 

This reference might help.

 

http://www.scribd.com/doc/16594538/2009-03-05-Glucose-Anomers

Edited by studiot
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+1, John.

 

I can't see how someone can have got this far in organic (or any other sort) of chemistry and be unable to balance a reaction equation.

 

 

 

Apparently you don't understand how Universe works.

 

Perhaps you have no idea what you were doing. You might want to figure that out first.

 

 

Exactly what good comes from mocking me?

A person comes looking for help and is subject to mockery and sarcasm. Well fuck off, I don't need this. Thanks for nothing.

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The criticisms are maybe a little harsh, but you can't fault them in their accuracy. You can't balance it because the equation isn't right. You claim this is an experiment you yourself performed. Just from a perspective of safety, don't you think you should have known what you were doing before you did it?

 

!

Moderator Note

Regardless, it's no need to need be vulgar in return. That is to stop.

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I'm sorry you have taken umbrage with my post.

It was not meant to be mocking, perhaps you might like to consider the old adage

 

Act in haste, repent at leisure.

 

 

Studiot

+1, John.

 

Not only did John Cuthber originally try to help your balancing efforts, but he also tried to calm less temperate comments.

He also told you exactly what was wrong with your balance and what needs to be done to correct this.

Though his replies are often very concise.

 

Studiot

I can't see how someone can have got this far in organic (or any other sort) of chemistry

 

 

Actually a compliment, this is not basic or elementary chemistry.

 

But balancing a chemical equation is basic.

 

Studiot

This reference might help.

 

http://www.scribd.co...Glucose-Anomers

 

 

 

Since John had already told you how, I took the trouble to find a reference to a similar if not identical reaction (your original desciption was not entirely clear) to help further.

Edited by studiot
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@OP,

It was unclear to me how you balanced this equation. Did you use some sort of a program? I suggest balancing the equation yourself and show us what you have. Without a properly balanced equation, the limiting reagent calculations are bound to fail.

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Can we please leave the details of balancing the equation aside until someone posts the right equation?

Here's a hint

http://en.wikipedia.org/wiki/Acetylation#/media/File:Aspirin_synthesis.png

 

Also, in order to maintain my reputation for being deliberately obscure, I will quote Shakespeare's play Julius Caesar

"It's all Greek to me"

and remind you of what I said about the product's name.

 

Incidentally, if I post something very "concise", check the time stamp. If it's near 07:00 I'm posting in a hurry before I go and catch a bus so please cut me a little slack.

Thanks

Edited by John Cuthber
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@OP, When an alcohol reacts with an anhydride, the general reaction is R'OH + RC(O)-O-C(O)R ==> R'-O-C(O)R + RC(O)OH. The main product is an ester, and one equivalent of an acid is the side product. This is a pretty generous hint toward balancing the equation, and it goes along with John Cuthber's hint.

Edited by BabcockHall
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