The mass of an erlenmeyer flask is 78.639g and the mass of the flask and water is 327.039. If the density of water is 1 g/ml then what is the true volume of the flask?

Question

so i had subtracted the mass of just the flask from the mass of the flask and the water and got 248.4. Would that be the amount of the volume in mL? Can you do the calculation for me so I can better understand this because i need to do something so that grams are cancelled out but that would involve doing 1/248.4 which doesn't make any sense when I have to use this calculation to do a different calculation regarding trying to find the molar mass of a liquid?

Also, why is it that one can use the ideal gas law to obtain the molar mass for a liquid since it only applies to gases that act under ideal circumstances. Is it because the liquid is turned into vapor anyways and the mass of the condensed vapor is equal to the mass of the gas? Can anyone explain this?

DrBob222 · Answer

First part. You have subtracted correctly and MASS of the water in the flask is 248.4 grams. Then since
mass = volume x density you can rearrange that to volume = mass/density
mass = 248.4g and density of the H2O is 1 g/mL (from the problem), then
248.4g/1 g/mL so volume is 248.4 mL. In this case the volume and the mass have identical values BECAUSE the density is 1 g/mL but if the density were any other value than 1g/mL the volume and mass would not be the same.

For the second part, I assume this is a follow up to your earlier post. Again, I'm not exactly sure of the experimental details but I think the liquid is supposed to evaporate and fill the flask with the vapor. As a vapor, the ideal gas law allows you to calculate the molar mass. Of course, you assume the gas is an ideal gas to do this.