[Gweedo8]

OK so I have this lab that went pretty quick and smooth and I have an online assessment that I needed to put all my figures in. I am all complete but am having trouble with 3 problems that the assessment is saying is wrong and I am looking for someone to verify or explain what I am doing incorrect.

Here were the steps of the lab and my findings:

Determining the molecular weight of Acetone:

Step 1: Obtain a Dumas bulb from the Equipment menu.

Step 2: Record the volume of the bulb in liters (volume is marked on bulb). .056L

Step 3: Record the mass the empty bulb using an electronic balance. 50.g

Step 4: Place 20 ml of acetone into the bulb.

Step 5: Obtain a 600-ml beaker.

Step 6: Select Beaker and place about 500 ml of water into beaker or enough to cover neck of bulb.

Step 7: Combine bulb with beaker (using combine menu option).

Step 8: Obtain a hot plate from Equipment menu.

Step 9: Place combined Dumas bulb and beaker assembly onto hot plate.

Step 10: Turn on hot plate to maximum heating setting.

Step 11: Allow all acetone to boil away and wait 1-2 minutes before removing bulb from beaker.

Step 12: After removing bulb from beaker, allow Dumas bulb to cool until acetone vapors have condensed (2-3 minutes).

Step 13: Weigh bulb and condensed vapor using an electronic scale and record result. 50.1062g

Then the lab told me to use this info to answer the assessment:

(i)  Volume of Dumas bulb (L): 56ml or .056L

(ii) Mass of empty Dumas bulb (g): 50g

(iii) Mass of Dumas bulb + condensed acetone (g):50.106

(iv) Mass of acetone gas required to fill bulb ((iii) - (ii)): .106

(v) Molecular weight of Acetone: Mass / n = Mass / (PV/RT) =  (Mass *R *T) /(P * V)  =.00183

Given:
Pressure: 1atm
Temperature: 373 Kelvin (boiling point of water)

Then Here was the question I needed to answer (which I am getting number 2,5 and 6 incorrect):

1)Weight of empty Dumas flask=50g
2)Weight of acetone=? I tried both 39.285 & .1062 and it says these are wrong
3)Weight of liquid vapor after condensing=.106
4)Moles of acetone vapor based on ideal gas law=.00183
5)Calculated molecular weight of acetone based on experiment. (Give in grams / mole).= I tried .072 and that's incorrect
6)%error from the theoretical molecular of acetone and the experimental value.=which to me seems like there is a 0% error

[sjb]

1)Weight of empty Dumas flask=50g
2)Weight of acetone=? I tried both 39.285 & .1062 and it says these are wrong
3)Weight of liquid vapor after condensing=.106
4)Moles of acetone vapor based on ideal gas law=.00183
5)Calculated molecular weight of acetone based on experiment. (Give in grams / mole).= I tried .072 and that's incorrect
6)%error from the theoretical molecular of acetone and the experimental value.=which to me seems like there is a 0% error

I don't know the theory behind the experiment, but again, in part v I think you are calculating the number of moles, rather than the molecular weight. So if you have 0.00183 mol, weighing 0.106 g, what is the molecular weight? (why not try with easier numbers, so it's a bit more obvious what manipulations to do, say 0.1 mol, weighing 10 g)