Question

Hello! T'm in Gen Chem II now, but unfortunately I had to take a semester off, so I'm a bit rusty. I'd be really grateful if somene could help me solve this and post a thorough explanation. Thank you!

The vapor pressure of diethyl ether (ether) is 463.57 mm Hg at 25°C. How many grams of aspirin, C9H8O4, a nonvolatile, nonelectrolyte (MW = 180.1 g/mol), must be added to 209.6 grams of diethyl ether to reduce the vapor pressure to 449.80 mm Hg ?

Answer 1

This is a problem of depression in vapor pressure [a colligative property]

depression in vapor pressure = iMRT

with,

i = 1 [Van't hoff factor]

density of diethyl ether = 0.713 g/ml

So volume of diethylether = g/density = 209.6/0.713 ml = 0.2096/0.713 L

M = molarity of solution = moles/L = g of aspirin x 0.713 g/ml/180.1 g/mol x 0.2096 kg = 0.019 x g

R = gas constant

T = 25 + 273 = 298 K

Feed values,

463.57 - 449.80 = 1 x 0.019 x g x 298

grams of aspirin to be added (g) = 2.43 g