[smexichiko]

I was wondering how you would use the molar volume at standard conditions to calculate the number of moles and then use the number of moles to solve for the molecular weight.

[billnotgatez]

This forum requires that you show some of your thoughts so we may see where you need help.
You also need to give better headings to your threads  (that is why I edited you heading)
Forum Rules: Read This Before Posting

[smexichiko]

Well what I was thinking is that since you know that 1 mol of gas occupies 22.7L. Then you would take the volume of the gas which was 0.05897L and divide it by 1mol/22.7L to find the number of moles. Then after that use the equation MW=m/n to find the molecular weight. The mass that was found for acetone in the lab was 0.0667g and 0.0874g, but when I use these values the molecular weight is like 10 to 20g/mol off from the accepted value of 58.08g/mol. So I am not sure if the values are off  because of the chance of error during the lab or if the method of how I calculated the molecular weight was wrong.

[Borek]

General logic is right. Hard to comment on accuracy not knowing details of the experiment. Are you sure you were expected to use just STP, and not the exact temperature and pressure?

[billnotgatez]

I played with your numbers to try and figure out where you went wrong
and it appears your weights were half of what they should be
Still doubling your weights there was error
Could you have read the scales wrong
maybe your volume is wrong by a factor of 2

0.1334g  0.0667g doubled
0.1509g  @22.7L = 1 Mole where 58.08g/mol
0.1529g  @22.4L = 1 Mole where 58.08g/mol
0.1748g  0.0874g doubled

[Borek]

Bill, it is too early to play with numbers, when they don't make sense. He gave us two masses, but one volume - so the information is incomplete.

Besides, I don't believe in the volume of the gas to be measured with 0.01 mL accuracy. Many things are dubious here.

[billnotgatez]

Many things are dubious here.

Very true

[smexichiko]

the volume was 58.97 ml before i converted it to liters because of significant digits when solving for the volume of the flask that contained the gas and yes we were to use stp conditions for this problem of the lab. the question for the lab was: An alternate method of calculation for this experiment would be to calculate the volume of the gas at standard conditions and then use the molar volume at standard conditions to calculate the number of moles of the unknown gas. Using this method,calculate the molecular weight of acetone.

The other way we calculated or MW was using the equation MW=mRT/PV. The temperatures were 97.77*C for the mass of 0.0667 and 96.06*C for the mass of 0.0874.

[smexichiko]

Also the density and pressure at the time of the experiment were o.9979955 g/ml and 0.9928 atm.

[Borek]

An alternate method of calculation for this experiment would be to calculate the volume of the gas at standard conditions

And how you calculated the volume of the gas at STP?

The other way we calculated or MW was using the equation MW=mRT/PV. The temperatures were 97.77*C for the mass of 0.0667 and 96.06*C for the mass of 0.0874.

OK, I think I was finally able to guess what you did - the experiment was to measure the weight of the gas occupying a given volume?

Any other details we are still missing?

[smexichiko]

The purpose of the experiment was to find the molecular weight of acetone and an unknown, which i was able to identify with no problem. I calculated STP using the formula v=nRT/P, where n=1mol, R= 0.08206Latm/Kmol,T=273K and P=1bar

[smexichiko]

Also there is not any more missing information that I can think of.

[Borek]

I calculated STP using the formula v=nRT/P, where n=1mol, R= 0.08206Latm/Kmol,T=273K and P=1bar

That's not what I asked about, but I see how my questions was ambiguous.

IMHO they want you to convert the known volume (58.97 mL) to the equivalent volume at STP (hint: no need for R), and then to use converted volume and the known value of the one mole volume to find number of moles.

[smexichiko]

So was what i was thinking from the start the right idea?

[Borek]

As far as I can tell - no.

You planned to use 58.97 mL as your volume:

you would take the volume of the gas which was 0.05897L and divide it by 1mol/22.7L

without converting it first to STP.