Sulfur hexafluoride gas is collected at 26.0 °C in an evacuated flask with a measured volume of 35.0 L. When all the gas has been collected, the pressure in the flask is measured to be 0.300 atm . Calculate the mass and number of moles of sulfur hexafluoride gas that were collected. Be sure your answer has the correct number of significant digits.

The mass of sulphur hexafluoride collected over water is:

MASS IS 115.28g

NUMBER OF MOLE = 0.04 mole.

Explanation:

Gas constant, R = 0.082 L atm/ mol K

Temperature =26° C = 26 + 273 K =>299 K

Pressure = 0.03 atm

Volume = 35 L

Using the ideal gas equation, we can calculate the number of moles and hence the mass from the mass, molar mass, number of mole relationship.

PV = nRT

Re-arrange by making 'n' the subject of the equation:

n = PV / RT

n = 0.03 * 35 / 0.082 * 299

n = 1.05 / 24.518

n = 0.0428

The number of moles is therefore 0.04 moles

Then we calculate the mass:

Number of moles = mass / molar mass

But before we do that, we must calculate the molar mass of the substance collected over water.

The substance is sulphur hexafluoride and has chemical formula SF6 ( S = 32, F = 19)

Molar mass of SF6 = ( 32 + 19*6)

Molar Mass = 146 g/ mol

Equate the values and then solve for the mass, we get:

Mass = number of moles * molar mass

Mass = 0.04 * 146

Mass = 115.28 g

So therefore, the mass of the sulphur hexafluoride is 115.28g and its number of moles is 0.04 mole.