last check:

(c) A wine cooler contains 4.5% ethanol by mass. Assuming that only the alcohol burns in oxygen, how many grams of wine cooler need to be burned to produce 3.12 L of CO2 (d = 1.80 g/L at 25°C, 1 atm pressure) at the conditions given the density?

1 C2H5OH + 3 O2 = 2 CO2 + 3 H2O
3.12 L CO2 * (1.80 g / 1 L) = 5.62g CO2
5.62 g CO2 * (1 mol / 44 g CO2) = 0.128 mol of CO2
0.128 mol CO2 * (1 mol of C2H5OH / 2 mol of CO2) = 0.064 mol C2H5OH
0.064 mol of C2H5OH * (46 g / 1 mol) = 2.944g C2H5OH
2.944g C2H5OH * (100 / 4.5) =
65.42 g of wine cooler

Is this right? thanks

3 answers

Is 1.80g/L the density of CO2 at standard conditions? If so, then that is correct, I believe.
I worked the problem and obtained 65.3. Your method is ok and the numbers look ok. I used molar masses that were a little different. Here is a site that does my calculation for me for molar masses.
http://environmentalchemistry.com/yogi/reference/molar.html
One final note. Your answer has four places in it but you are allowed only three since 3.12, 1.80 and 4.5(and I presume that is 4.50) have three places.
Great work guys! I read somewhere that people were using PV = nrt ... do you know why ?