posted by .

You mix 40.0 g of ethanol (C2H5OH, molecular weight = 46.1 g/mol) and 60.0 g of water (molecular weight = 18.0 g/mol) The resulting solution has a density of 920 g/L.

a)Calculate the molarity of ethanol in this solution?
Answer : 0.06 kg of H2O

This is correct.

b) At what temperature will the solution freeze? Pure water freezes at 0.00 degrees C and its Kf= 1.86 degrees C/m. Hint: ethanol is not an ionizing solute.

My work: delta Tf= i*Kf* Msolute
1.186* 14.5
delta Tf= 26.97
=26.97 degrees C

This is correct.

I need help on part c and d:

c) calculate the molarity of ethanol in this solution

d) What pressure needs to be applied to this solution at T= 0 degrees C to make water come out from it through a water-permeable membrane?

Please help!


    You have 40.0 g ethanol in 40+60 = 100 g soln. You know the density of the solution; volume = mass/density and convert to L. You have moles ethanol from an earlier part. M = moles/L soln.

    d. pi = MRT


    for part c:

    100g* 1L/920 g= .108695 L

    0.87 mols of H2O/.108695 L

    =8.004 M

    Is this right?

    part d:

    pi= (8.004M) (0.08206) (-26.97+273)= 161.59 atm

    is this right?


    c looks ok but I don't understand why you have the line 0.87 mols of H2O/.108695. You have moles ethanol already and you have volume already. You don't need this line nor the calculation.

    I don't agree with your answer from a. 0.06 kg is mass of solvent but it isn't molarity (or molality).

    Also, I don't agree with b. It can't possibly be -26.+ which makes d wrong before I even look at it. And while I'm at it, please note that I discourage you from using i*Kf*Msolute. M means molarity. m means molality and m is what goes there.


    sorry I typed it answer for a) is 14.5 M


    what did you get for part b then?


    oohhh so for part d I mixed up molarity and molality my bad...I get it now! So the answer I got in part a is supposed to be used in part d......Thanks! :)


    What did you get for part b if you disagree with -26?


    No, the number in a is m and the number to be used in d is M. Your 8.00 is ok there. Its the -26.97 that stopped me. And your answer for part a is 14.5 m; i.e., 14.5 molal.
    For b part I have
    dT = i*Kf*m
    dT = 1*0.186*14.46
    dT = 2.6898 which I would round to 2.69 which makes the soln freeze at -2.69 C.


    But Kf= 1.86 degrees C/m not 0.186? So shouldn't it be :
    dT = 1*1.86*14.46 =26.97
    ---> -26.97


    You are right and I am wrong. I don't know how that crept into my mind. I've worked a problem like this a million times. Let me look at the last problem.


    Okay thanks sooooo much! I really really really appreciate your help! It's fine everyone makes mistakes! :)


    I went back and re-read the problem and it says that you want all of that info AT T= 0 degrees C so I think you want 273 for T and not delta T.
    With regard to part a, I think I got pushed off the bus on part a when I saw the 0.06 and that skewed my thinking. Sorry about that.


    No problem! Thanks! :)

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Chemistry II

    A solution of ethanol in water is prepared by dissolving 61.0 mL of ethanol (density = 0.79g/mL) in enough water to make 280.0 mL of solution. What is the molarity of the ethanol in this solution?
  2. Chemistry

    The molecular weight of glucose is 180.2 and the molecular weight of lactose is 342.3. What is the molarity of a 25% glucose solution?
  3. Chemistry

    The density of an aqueous solution containing 10% of ethanol (C2H5OH) by mass is 0.984 g/ml. A) Calculate the molality of this solution. B) Calculate its molarity. C) What volume of the solution would contain 0.125 mol of ethanol.
  4. chemistry

    What is the molarity of 100 ml of ethanol dissolved in 1.5 liters of water?
  5. Chemistry

    Distillation Scale up: In an experiment 100 lb-mol of 47 lb-mol % ethanol, 53 lb mol % water sol'n is fed into distillation column and separated into two streams: 100lb-mol 0.470 lb-mol ethanol 0.530 lb-mol water goes to: steam 1: …
  6. chemistry

    What is the molarity of 100ml of ethanol dissolved in 1.5L of water?
  7. Chemistry #11

    A solution of ethanol (C2H5OH) is prepared by dissolving 35.0 ml of ethanol in enough water to make 120.0 ml of solution. What is the molarity of the ethanol in this solution?

    An ethanol-water solution is prepared by dissolving 10.00 ml ethanol C2H5OH (density=0.789g/ml) in sufficient water to produce 100.00 ml of solution with a density of 0.982g/ml. What is the concentration of ethanol in this solution?
  9. Analytical Chemistry

    A 10.0 mL sample of whiskey was diluted to 500.0 mL. A 4.00 mL aliquot of the diluted sample was removed and the ethanol, C2H5OH, was distilled into 50.00 mL of 0.02150 M K2Cr2O7 and oxidized to acetic acid. The excess Cr2O72– was …
  10. chemistry

    When 25 mL of C2H5OH (density 0.80 is dissolved in water to prepare a 250 mL solution, the density of the solution was found to be 0.950 Calculate a. Molarity of pure ethanol; b. Molarity of ethanol in the final solution; …

More Similar Questions