A sample of sodium sulfate, Li2SO4, contains 6.78 x 10^23 formula units.

Question

How many moles of Li2SO4 are there in the sample?
How many moles of Li+ ions are there in the sample?

Answer 1

You made a typo wring sodium sulfate but typing Li2SO4. I assume you meant Li2SO4.
1 mol contains 6.022E23 molecules so
6.78E23 molecules x (1 mol/6.022E23 molecules) = mols Li2SO4.

There are two Li^+ per 1 molecule Li2SO4; therefore, there must be twice mols Li&+ must 2x mols Li2SO4.

Answer 2

I don't understand where you are getting 6.022E23 from

Answer 3

That is a constant. It's just another unit like a dozen of something (12) or a gross of sometihig (144 or 12 dozen) or a ream (500 sheets paper). In this case there are 6.022E23 molecules in a mole of molecules, 6.022E23 atoms in a mole of atoms, 6.022E23 bananas in a mole of bananas, 6.022E23 cars in a mole of cars, 6.022E23 grains of sand in a mole of sand grains, etc. The reason you don't hear that much in everyday life is that the number is so huge that we don't come into contact with so many of one thing unless those things are extremely small (as in the case of atoms and molecules).