Counting by mass and converting to moles

Question

How many molecules are in 74.092 grams of Ca(OH)2?

Answer 1

First, convert the mass to moles of Ca(OH)₂ using the molecular weight.

Use this mole amount to convert to molecules using avogadro's number which tells you there are 6.022*10²³ molecules in 1 mole.

MW of Ca(OH)₂ = 40.08+2*16+2*1 = 76.08g/mol

74.092/76.08 = 0.974 moles

0.974 * 6.022*10²³ = 5.86*10²³ molecules