A gas mixture is made by combining 7.4 g each of Ar, Ne, and an unknown diatomic gas. At STP, the mixture occupies a volume of 18.28 L.
What is the molar mass of the unknown gas? = g/mol
Given
Pressure = 1 atm ( at STP)
Temperature = 273.15 (at STP)
Volume = 18.28 L
Now consider, PV = nRT
1 x 18.28 = n x 0.0821 x 273.15
n = 18.28 / 22.4
= 0.816 mole
Number of moles of Argon = Mass / Molar mass
= 7.4 / 39.95
= 0.185mol
Number of moles of Ne = mass / molar mass
= 7.4 / 20.18
= 0.3666 mol
Number of moles of unknown gas = 0.816 -0.185 - 0.3666
= 0.26 mol
The molar mass of an unknown gas is = mass / Moles of unknown
= 7.4 / 0.26
= 28.4 g / mol
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