A gas mixture is made by combining 5.7 g each of Ar , Ne , and an unknown diatomic gas. At STP, the mixture occupies a volume of 12.88 L. What is the molar mass of the unknown gas?

The molar mass of unknown diatomic gas is 38 grams

Explanation:

At STP:

The temperature and pressure conditions are 273 K and 1 atm respectively.

To calculate the number of moles, we use the equation given by ideal gas equation:

PV = nRT

P = Pressure of the gas  = 1.00 atm

V = Volume of the gas = 12.88 L

n = number of moles of mixture = ?

R = Gas constant =

T = Temperature of the gas

Putting values in above equation, we get:

To calculate the number of moles, we use the equation:

    .....(1)

Given mass of argon = 5.7 g

Molar mass of argon = 39.95 g/mol

Putting values in equation 1, we get:

Given mass of neon = 5.7 g

Molar mass of neon = 20.2 g/mol

Putting values in equation 1, we get:

Moles of unknown diatomic gas = [0.575 - (0.143 + 0.282)] = 0.150

Now, calculating the molar mass of unknown diatomic gas from equation 1, we get:

Given mass of unknown diatomic gas = 5.7 g

Moles of unknown diatomic gas = 0.150 moles

Putting values in equation 1, we get:

Hence, the molar mass of unknown diatomic gas is 38 grams