Diatomic Mole Calculations?

Question

To find moles with Cl2, AMUs 71, do you divide mass by 35.5 or 71?

Answer 1

Moles = grams / molar mass

A Cl2 molecule is made up of two Cl atoms which have a mass of about 35.5 AMUs each, so the TOTAL mass of a Cl2 molecule is 71 AMUs, or 71 g/mol which is the unit you actually want here.

So, 71 g/mol is the value to use.