A 4.35-g sample of gas has a density of 1.45 g/L when placed in a 3.00-L container at 21.0°C and 1.25 atm. What is a possible molecular formula of the gas? The value of R = 0.0821 L atm mol^-1 K^-1.

Question

Quizplus · Accepted Answer

We can use the ideal gas law to calculate the number of moles of the gas:
PV = nRT
n = PV/RT = (1.25 atm)(3.00 L)/(0.0821 L atm/mol K)(294 K) = 0.142 mol
Next, we can use the density to calculate the molar mass of the gas:
density = mass/volume = molar mass(P)/RT
molar mass = (density)(RT)/P = (1.45 g/L)(0.0821 L atm/mol K)(294 K)/(1.25 atm) = 32.1 g/mol
Now we can look at the possible molecular formulas and calculate their molar masses:
A) CH4: molar mass = 16.0 g/mol
B) Cl2: molar mass = 70.9 g/mol
C) CO: molar mass = 28.0 g/mol
D) O2: molar mass = 32.0 g/mol
E) NO: molar mass = 30.0 g/mol
We can see that the only molecular formula with a molar mass close to 32.1 g/mol is CO, so the answer is C.

A 435-G Sample of Gas Has a Density of 1