How do you convert molecules to grams and vice versa? ?

I hated chemistry in high school. My teacher was awful. At any rate, you want to try and get everything you start off with (in this case, 25.0 g of H2SO4) to mole before converting anywhere else. So you would multiply it by avagadro's number (6.02x 10 to the 23rd power). Then you would multiply this number by how many total molecules are in H2SO4 (2 hydrogens plus 4 sulfates).