A) Calculate the density of oxygen, O2, under each of the following conditions:

Question

A) Calculate the density of oxygen, O2, under each of the following conditions:

STP

1.00 atm and 30.0 ?C

Express your answers numerically in grams per liter. Enter the density at STP first and separate your answers by a comma

B) To identify a diatomic gas (X2), a researcher carried out the following experiment: She weighed an empty 1.2-L bulb, then filled it with the gas at 1.60atm and 21.0 ?C and weighed it again. The difference in mass was 2.3g . Identify the gas

Express your answer as a chemical formula.

Explanation / Answer

Part A)

1)

Pressure = 1 atm

Temperature = 273 K

Molar mass of O2 = 32 g/mol

We have,

pV=nRT

or

pV=(mass/molar mass)xRxT

or

p x molar mass=(mass/V)xRxT

or

p x molar mass = density x R xT

By substituting the values,

1 x 32.0 = density x 0.0821 x 273 K

Density = 1.43 g/L

2)

Pressure = 1 atm

Temperature = (30 + 273) K = 303 K

Molar mass of O2 = 32 g/mol

We have,

p x molar mass = density x R xT

By substituting the values,

1 x 32 = density x 0.0821 x 303 K

Density = 1.29 g/L

Part B)

Volume = 1.2 L
Pressure = 1.6 atm
Temperature = 21 + 273 = 298 K
R = 0.0821 atm L/mol K
therefore, number of moles of gas, n = PV/RT = (1.6 x 1.2)/(0.0821 x 298) = 0.07847 mol
Mass of the gas, W = 2.3 g
Therefore, molar mass of the gas = W/n = 2.3/0.07847 = 29.31 g/mol
Since, this is a diatomic molecule, mass of a single molecule = 29.31/2 = 14.65 amu
Mass of nitrogen atom is 14 amu.
Therefore, the diatomic gas is N2

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