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!
"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!
Answers
DrBob222
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.
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.