How do you know whether or not the H at the beginning of the formula of an acid gets a 2 or not?

The valence of the -NO3 radical is -1, a spare electron, balanced by Hydrogen having a spot for a received electron, electrons having a negative charge of -1. So HNO3 balances. The -SO4 radical has two extra electrons, needing two electron "spots" to end up balanced at H2SO4, requiring two hydrogen atoms. Copper sulfate CuSO4 works because copper usually has a valence of +2 (in its common form). But that's the cupric form, and the cuperous form is +3, which can sneak up on you! Cuperous sulfate would be Cu2(SO4)3. Regards, Larry.