How many moles are in 50g of NaCl.

Using the formula mass=Mr * moles we can rearrange this so it equals moles= mass / Mr. We are told the mass of the NaCl is 50g however we need to work out the Mr (relative formula mass) of the NaCl too. We do this by looking up the relative atomic masses of Na and Cl in the periodic table. Na has an atomic mass of 23 and Cl is 35.5. So the Mr(NaCl)= 23 + 35.5 = 58.5. Putting all of this into our moles equation gives us the answer: moles= 50/58.5 = 0.855 moles (3sf).