Question

A flask has a volume of 159.6 mL . When filled with air at a pressure of 749.2 torr and a temperature of 25.54 ∘C, the flask and air have a mass of 55.598 g . When filled with carbon dioxide at the same temperature and pressure, the mass of the flask and CO₂ is 55.699 g .

What is the mass of the carbon dioxide gas in the flask (when the flask is filled with carbon dioxide)?

What is the mass of the flask alone?

What is the density of the air?

Answer 1

Since flask has a volume of 159.6mL, so air or CO₂ will occupy the same volume.

So, P = 749.2 torr = 0.9858 atm (1torr = 0.001316 atm)

V = 159.6mL = 0.1596L

T = 25.54^oC = 298.69K , R = 0.08206 L atm K^-1 mol^-1

To find moles of CO₂ in the flask using ideal gas equation: PV = nRT

n = PV/RT = (0.9858 atm)(0.1596L)/ (0.08206 L atm K^-1 mol^-1)(298.69K) = 0.0064 mole

molar mass of CO₂ = 44g/mol

mass of CO₂ = molar mass of CO₂ X moles of CO₂ = 44g/mol X 0.0064mol = 0.2824 g

The mass of the carbon dioxide gas in the flask = 0.2824g

the mass of the flask + CO₂ = 55.699 g

The mass of flask = 55.699 - mass of CO2 in the flask = 55.699g - 0.2824g = 55.4166 g

The mass of the flask alone = 55.4166g

the mass of flask + air = 55.598 g

Mass of air in the flask = 55.598 - mass of flask alone = 55.598 - 55.4166 = 0.1814g

density of air = mass of air / volume of air = 0.1814g /159.6mL = 0.001136 g/mL

The density of the air = 0.001136g/mL