Homework Help: Chemistry

Posted by Shannon on Wednesday, April 6, 2011 at 11:46pm.

An empty flask weighs 128.632g. After vaporization of a sample of volatile liquid, at a measured temperature of 99.8 C. The flask is sealed, cooled to room temperature, and weighed. The mass is now 129.225g. The measured P atm is 757.7 torr. The flask is rinsed and filled completely with water at 21.8 C. The mass of the flask is now 381.676g.

1. Calculate the volume of the flask from the mass of the water contained in the flask and the density.

2. Calculate the molar mass of the volatile liquid.

Chemistry - DrBob222, Thursday, April 7, 2011 at 12:14am
Can you do #1? volume = mass/density
#2. Use PV = nRT and solve for n = number of mols.
Substitute into moles = grams/molar mass. You have grams (from the mass flask + vapor - mass empty flask) and moles. Solve for molar mass.
Chemistry - Shannon, Thursday, April 7, 2011 at 12:52am
for #1, we have to find the density first right? so density is mass/volume, so from there you take 381.676 and divide that by..

and thats where im lost :(
Chemistry - DrBob222, Thursday, April 7, 2011 at 1:02am
Close but no cigar.
381.676 = mass flask + water
-128.632 = mass empty flask
---------
difference = mass water
volume of flask = mass water/density water = ??
Chemistry - Shannon, Thursday, April 7, 2011 at 1:23am
sorry to be asking too much but how do we get the density of water?

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