Question

An unknown homonuclear diatomic gas has a volume of 2.5L at standard conditions of temperature and pressure, and it has a mass of 3.571g. What is the molecular formula for the gas

Answer 1

Answer: 16g/mol; O2

Explanation:

The gas has a volume of 2.5L at STP, so the number of moles can be determined as follows.

n=2.5L×1mol/22.4L=0.1116mol

The mass is given to be 3.571g. The molar mass of the unknown gas can be determined by dividing grams by moles.

3.571g/0.1116mol=32.00g/mol

The gas is a homonuclear diatomic gas, so the gas must contain two atoms with a molar mass of 32g/mol/2=16g/mol. This is the molar mass of the element oxygen, so the gas is diatomic oxygen, O2.