The following procedure provides a crude method of determining the molar mass of

Question

The following procedure provides a crude method of determining the molar mass of a volatile liquid. A liquid of mass 0.0171 g is introduced into a syringe and the end is capped (sealed). The syringe is transferred to a temperature bath maintained at 62.7 °C, and the liquid vaporizes. As the liquid vaporizes the plunger is pushed out. At equilibrium, the plunger reads 6.81 mL of gas. AtmospheriC pressure is 740. mmHg. What is the approximate molar mass of the compound (in g/mol)? Hint is given in the feedback Answer

Explanation / Answer

740 mm Hg = 0.97368 atm

Assuming ideal behavior for the vapor

then

PV=nRT

R = 0.082 L. atm mol-1K-1

T = 273.15 + 62.7 = 335.85 K

V = 6.81x 10-3 L

n=  0.97368 x 6.81x 10-3/ (0.082 x 335.85 ) = 0.2407 x 10-3moles

Number of moles = mass /molar mass

mass = 0.0171 g

molar mass = 0.0171/0.2407x 10-3 = 71.04 g/mol

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