Question

How many moles of NaCl are in 75.0 g of NaCl ?

Answer 1

To find the number of moles of any compound you should divide the mass over the molar mass of that compound

so for your question,

number of moles = mass/ molar mass
= 75.0 g / 58.443 g/mol
= 1.2833
= 1.28 and note that the answer is rounded to 3 significant figures

Answer 2

number of moles is found by formula n=mass/molar mass, or m/M. the molar mass is found by adding together the atomic masses of Na and Cl (22.99 + 35.45) to give 58.44 g/mol. Since the mass of NaCl is 75.0g, we find the number of moles as follows:
n = 75.0 / 58.44 = 1.28 mol