400 ml of a gas (@STP) has a mass of 0.792 g. What is the molecular mass of this gas?

Answer 1

Molecular weight is grams/moles, so we need to know grams and moles. We are given the grams (0.792 g), so we need to find moles. At STP 1 mole of ideal gas = 22.4 L. Since we have 400 ml (0.400 L), we can find moles. 0.400 L x 1 mole/22.4 L = 0.01786 moles

Molecular mass = 0.792 g/0.01786 moles = 44.3 g/mole (to 3 significant figures)