Posted by Gloria on Tuesday, July 30, 2013 at 11:09am.
A 5ml portion of table wine was diluted to 100 ml in a volumetric flask. The ethanol in a 20 ml aliquot was distilled into 100 ml of 0.05151M K2Cr2O7. heating completed oxidation of the alcohol to acetic acid:
Ch3Ch2OH + 2Cr2O7(2-) +16H(+) -> 3Ch3COOH + 4Cr(3+) + 11H2O following which the excess dichromate was titrated with 14.42mL of 0.02497M Fe(II). Calculate the weight-volume percentage of ethanol.
So i tried doing this problem and again, i don't know how to continue (if i even started right)
Cr2O7(2-) + 3Fe(2+) -> Cr(3+) + 3Fe(3+)
now i don't know how to continue :S
- Analytical chemistry - DrBob222, Tuesday, July 30, 2013 at 3:37pm
You have made several errors. The way this works is that too much dichromate was used in the oxidation of ethanol to acetic acid. How much too much. That is what the back titration with Fe does--it tells you how much too much.
1. mols Cr2O7^2- = ok
2. You can't calculate mols EtOH from this (yet).
3. The Fe/Cr2O78^2- is not balanced.
6Fe^2+ + Cr2O7^2- ==> 2Cr^3+ + 6Fe^3+
Then mols Fe = 0.01442*0.02497 = about 0.00036 (but you need to go through more accurately). mols Cr2O7^2- from the Fe titration is 1/6 thast which = about 0.00006.
mols Cr2O7^2- used in the ethanol reaction = 0.005151-0.00006 = ?. Again, you need to go through this more accurately.
Then net mols Cr2O7^2-/2 = mols EtOH.
That times 46 g/mol converts to grams in the 20 mL portion you titrated.
Multiply that by 5 to determine grams in the100 mL volumetric flask (which is also grams in the original 5 mL), then multily by 20 to find the amount in 100 mL of wine. I get 11.71.
- Analytical chemistry - Gloria, Tuesday, July 30, 2013 at 6:14pm
Thank you very much for your help :)
Answer This Question
More Related Questions
- Analytical Chemistry - A 10.0 mL sample of whiskey was diluted to 500.0 mL. A 4....
- science(chem) - I'm making different concentrations of ethanol and I just wanted...
- Chemistry - A 15.0 mL sample of whiskey was diluted to 500.0 mL. A 3.00 mL ...
- Chemistry - Mass of an aspirin tablet is 0.42g and contains 77.38% ASA by mass. ...
- Chemistry - Suppose you dilute 20.0 mL of a 0.130 M solution of Na2CO3 to ...
- molarity - An aspirin tablet weighing 0.475 g has been analyzed and contains 68....
- Chemistry - Calculate mass of iron in tablet by spectroscopy? I have to ...
- chemistry - (3 pts) The stockroom prepared a solution by dissolving 0.2300 g of ...
- college chemistry - A 0.300 g sample of an aspirin tablet is used to prepare 100...
- Chemistry - An aspirin tablet weighing 0.475 g has been analyzed and contains ...