[keetner]

Hello,

Specifically about Grignards...I'm a little confused as to how you find the percent yield.
Reaction was as followed:


So I do know that my limiting reagent is the bromobenzene. I started with 10.4g and multiplied it by it's MW, giving me 0.06623 mols. However, I am confused because my TA mentioned something about having to find the molar ratio between each reaction - but isn't the molar mass just 1:1 between each step? So really, couldn't I just take 0.06623mol x (1mol benzoic acid/122.13g), giving me a theoretical yield of 8.08g? Then I do the whole percent yield bit.

And because it's 1:1, I can also figure out theoretically, how much of starting material, grignard reagent, and final product should have reacted/gotten. Actually, I'm thinking this is maybe what my TA meant...because I've only calculated the starting material and final product...but not actually how much grignard reagent could have/actually did react. But if this is the case, the thing that confuses me is the third compound...what exactly is it? Because I know that a bond between the O and MgBr sort of exists...but it's not a "true" ionic bond...

One more thing: What is the difference between gram atom and gram mole? It just mentioned it in the lab somewhere...and I can't seem to get a clear cut answer as to what it is.

Anyways, sorry this was so long and if it's a bit difficult to read...any comments/help would be greatly appreciated though.

Thank you!

[voidSetup]

If this is theoretical then yes overall the reaction is 1:1 the whole way through so the number of moles of bromobenzene is how many moles of benzoic acid you should have.  The third compound isn't something that is actually isolated, it describes how the benzoic acid looks before the acid workup protonates the carboxylic acid.

Also, I read gram-atoms in a paper the other day and was confused by it and found it somewhere.  It's an old term that means the same thing as moles.  A gram mole is a mass of substance in grams that is equal to its molecular weight.  So one gram mole of H2O is 18g.