So, here you have to look at the periodic table and see what the molar mass of each molecule composing the water compound [tex]H_2 O [/tex]
its two hydrogen atom plus an oxygen molecule, making it about 18g per mol.
That said, looking at the mass, we have to ask ourselves, if a mol of water contains 18g of mass, how many moles do we have in 0.5g of water?
We just do a cross multiplication:
[tex] \frac{(0.5)}{18} =0.027 mol[/tex]
