Question

Why is the formal charge of sulfur on sulfuric acid 0 (would be appreciated if you could work it out) and what do we do when calculating formal charge and we see a double bond?

Answer 1

As a reference, use the following drawing I made:

First remember that both oxygen and sulfur have 6 valence electrons, each. So they can be organized as in the drawing to get the best structure. Now focusing on the sulfur, notice only the electrons in the green area. The formal charge would then be the actual number of electrons of the element minus the number of electrons that are given in the structure. So 6-6=0.

Now, as for the oxygens, all in pink, you can see they also have 6 electrons each, because of the double bonds or their interaction with hydrogen. So their formal charge is also 6-6=0.

By calculating the formal charge of each element you can see that the total formal charge is actually 0. Now as to the question of the double bonds, you must consider that there are 4 electrons involved in them, two of them acting as the ones of one of the atoms and the other two to the other. It is easier to see this when adding the elctrons as dots (in blue).

The fact that you have double bonds is why the formal charge of sulfur is 0. If not for them, sulfur would only bond to the 4 oxygens and get a formal charge of 6-4=2.