Question

Boron trifluoride gas is collected at -1.0 °C in an evacuated flask with a measured volume of 25.0 L. When all the gas has been collected, the pressure in the Mask is measured to be 0.490 atm. Calculate the mass and number of moles of boron trifluoride gas that were collected. Round your answer to significant digits. mass: 0 mole: mol x 5 ?

Answer 1

Given:

P = 0.49 atm

V = 25.0 L

T = -1.0 oC

= (-1.0+273) K

= 272 K

find number of moles using:

P * V = n*R*T

0.49 atm * 25 L = n * 0.08206 atm.L/mol.K * 272 K

n = 0.5488 mol

Molar mass of BF3,

MM = 1*MM(B) + 3*MM(F)

= 1*10.81 + 3*19.0

= 67.81 g/mol

use:

mass of BF3,

m = number of mol * molar mass

= 0.5488 mol * 67.81 g/mol

= 37.22 g

Answer:

Mass = 37.2 g

Mol = 0.549 mol