Part A: Calculate the density of oxygen, O 2 , under each of the following condi

Question

Part A:

Calculate the density of oxygen, O 2 , under each of the following conditions: STP 1.00 atm and 25.0 C Express your answers numerically in grams per liter. Enter the density at STP first and separate your answers by a comma.

Part B:

To identify a diatomic gas ( X 2 ), a researcher carried out the following experiment: She weighed an empty 4.4- L bulb, then filled it with the gas at 1.90 atm and 29.0 C and weighed it again. The difference in mass was 9.5 g . Identify the gas. Express your answer as a chemical formula.

Explanation / Answer

Part-A

STP conditions are usually given as a pressure of 1 atm and a temperature of 0C. Under these conditions, 1 mole of any ideal gas occupies 22.4 L

Molar mass of Oxygen gas = 32.0gmol1

Density of O2 gas at STP = mass / volume = 32/22.4 = 1.4258 gL1

At P=1.00 atm T=25.00C = 298 K n=1 mole R=0.0821 L.atm.mol-1K-1

V=nRT/P = 1 x0.0821 x298/1 = 24.46 L

Density of O2 gas at P=1.00 atm T=25.00C = mass / volume = 32/24.46 = 1.3082 gL1

Part-B

P= 1.9 atm    V=4.4 L    T=290C = 302 K   R=0.0821 L.atm.mol-1K-1

n= PV/RT = (1.9 x 4.4)/(0.0821 x 302) = 0.337

Moles n= mass/mol.mass

          Mol.mass of X2= mass/moles = 9.5/0.337 = 28.18 grams

The gas is nitrogen and the formula is N2

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