A flask with a mass of 147.21 g is filled with a sample of volatile liquid is he

Question

A flask with a mass of 147.21 g is filled with a sample of volatile liquid is heated to 98°C. Upon cooling the new mass of the flask with the recondensed liquid is found to be 147.68 g. The volume of the flask is determined to be 135.6 mL and the atmospheric pressure is 743.5 torr. Calculate the molar mass of the volatile liquid.

If there was an error in the pressure measurement in the Problem #1 above, such that the atmospheric pressure was in reality lower than that measured, how would this affect the value determined for the molar mass?

Explanation / Answer

We apply ideal gas law, pV = nRT, then calculate number of moles.

P = pressure =743.5 Torr = 0.9782 atm ( given pressure converted to atmospheres of pressure)
V = volume =135.6ml = 0.1356 L
n = mol = ?
T ( kelvin Temperature) = 371 K
R = gas constant =0.0821 L-atm/mole-K

n = PV / RT
= 0.9782x 0.1356 L / 0.0821 x 371 K
= 0.004354 moles

mass of gas remaining flask = 147.68 g - 147.21 g
= 0.47 g which must be equal to the moles calculated.

number of moles = mass / molar mass
So molar mass = mass / moles
= 0.47 g / 0.004354 mol
= 108 g/mol

I f there was an in error in calculating the pressure as lower then number of moles will come down so that mola mass will seem HIGHER.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.