Question

I am struggling with organizing stoichiometry problems; I know how to solve them after they're set up. Here is an example:
"An organic compound with a FW of 417 was analyzed for ethoxyl {CH3-CH2O-} groups with the rxn:
ROCH2CH3 + HI --> ROH +CH3CH2I
CH3CH2I + Ag + H2O--> AgI +CH3CH2OH
A 25.42mg sample produced 29.03mg of AgI. How many ethoxl groups are there in each molecule?" Please help!

Answer 1

How many mols of the compound do you have? That is mols = g/molar mass = 0.02542 g/417 = ??

Now how many mols AgI was formed. That is
0.02903 g/molar mass AgI = zz

Therefore, you know zz mols AgI must have formed from zz mols CH3CH2I and in turn from (CH3CH2O)xR where x represents the number of the ethyoxyl groups in the original compound.

So what is x; that is, how many of the CH3CH2O- groups are in the original compound?
(mols ethoxyl groups/mols orig compound) = yy which will be close to a whole number. I worked the problem and came out with 2.02. Round that to a whole number, in this case, 2.00 and that will be the number of CH3CH2O- groups in the ROCH2CH3 compound at the beginning. Or to put it another way, the R(OCH2CH3)x compound must be R(OCH2CH3)2.