What molar quantity is represented by a #5.75*g# mass of sodium?
For all these problems we take the quotient.....
And note the dimensional consistency of the answer....i.e.
How did I know the molar mass of sodium? How will you know it if you are asked in an exam?
And to get the molar mass of sodium, chlorine, and copper, I look at that thing that tells me the molar masses of these elements. I forget its name....and I get molar masses of
Note that chlorine is commonly encountered as the diatomic molecule, i.e.