Question

What is the molar mass of an unknown gas with a density of 4.95 g/L at 1.00 atm and 25.0 °C?

Answer 1

Answer:

121 g/mol

Explanation:

To find the molar mass, you first need to calculate the number of moles. For this, you need to use the Ideal Gas Law. The equation looks like this:

PV = nRT

In this equation,

-----> P = pressure (atm)

-----> V = volume (L)

-----> n = moles

-----> R = constant (0.0821 L*atm/mol*K)

-----> T = temperature (K)

Because density is comparing the mass per 1 liter, I am assuming that the system has a volume of 1 L. Before you can plug the given values into the equation, you first need to convert Celsius to Kelvin.

P = 1.00 atm                         R = 0.0821 L*atm/mol*K

V = 1.00 L                             T = 25.0. °C + 273.15 = 298.15 K

n = ? moles

PV = nRT

(1.00 atm)(1.00L) = n(0.0821 L*atm/mol*K)(298.15 K)

1.00 = n(0.0821 L*atm/mol*K)(298.15 K)

1.00 = (24.478115)n

0.0409 = n

Now, we need to find the molar mass using the number of moles per liter (calculated) and the density.

0.0409 moles           ? grams           4.95 grams
----------------------  x  ------------------  =   ------------------
        1 L                       1 mole                     1 L

? g/mol = 121 g/mol

**note: I am not 100% confident on this answer