A beryllium X-ray window weighing 3.24 g contains 0.360 mol of beryllium. What is the molar mass of beryllium?

1. Moles are mass divided by molar mass, so molar mass is mass divided by moles. 2. Substituting gives molar mass = 3.24 g / 0.360 mol. 3. Carrying out the division gives 9.00 g/mol. 4. Units confirm the arrangement, since grams divided by moles leaves grams per mole. 5. The value 11.1 g/mol is the reciprocal 0.360 / 3.24 scaled up, which inverts the ratio. 6. The value 1.17 g/mol multiplies the two numbers instead of dividing them. _Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.1 Formula Mass and the Mole Concept_