Stoichiometry, Moles, and Molecular Weight

Problem:  How is the number of moles of a substance determined from its mass?
Answer:  Divide the mass in grams by the molar mass of the substance.

For 52.3 grams of CdSe: (using the factor-label method)

1 mole of CdSe = 191.37 grams CdSe

52.3 grams of CdSe X 1 mol CdSe/191.37 grams CdSe = 0.273 moles CdSe