How to convert grams to moles?

Question

Please explain very clearly. Thanks!!

Answer 1

Multiply by the gram-molecular weight. For example: How many moles are there in 500g NaOH? Atomic weights: Na=23, O=16, H=1, NaOH=40.

500gNaOH x 1molNaOH/40gNaOH = 12.5molNaOH

The 500g NaOH is given. The next factor comes from the molecular weight. The gNaOH cancel, leaving moles NaOH.

Answer 2

A Mole = the amount of substance whose mass is numerically equal to the substance's formula weight.
Examples:
Fe has an atomic weight of 55.85 so 1.00 mole of Fe would have a mass of 55.85 grams. If you have 20 grams of Fe, you would have 20/55.85 moles of Fe or 0.3581 moles.
NaCl has a formula weight of 58.45 so 1 mole of NaCl has a mass of 58.45. If you had 10.0 grams of NaCl you would have 10/58.45 moles or 0.1711 moles.
The molarity of a solution is equal to the number of moles of solute per 1 liter of solution. If you had 350 mL of 0.250 Molar NaCl solution you would have 0.350 x 0.250 moles of NaCl or 0.0875 moles which would be equal to a mass of 0.0875 x 58.45 or 5.11 grams of NaCl.