Question

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.

Answer 1

The mass of sulphur hexafluoride collected over water is:

MASS IS 115.28g

NUMBER OF MOLE = 0.04 mole.

Step-by-step 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.