Question

why does h2so4 break up to h+ and hso4-?

Answer 1

This molecule has 2 pkas. At different pH values, one of the hydrogens get deprotonated (remove 1 hydrogen). As you increase the pH to a higher value than the pka of the 2nd hydrogen, the 2nd hydrogen will be removed from sulfate.

Answer 2

it breaks up into H+ and HSO4- because H2SO4 is a strong acid (sulfuric acid) and it completely deionizes in solution

Answer 3

Your key to understanding is that it only does this in water solution. Otherwise, e.g. if you have pure H2SO4, the molecule is perfectly stable. That tells you the behaviour of water is critical here.

What happens is that the oxygen in water is "hungry" for electrons, being a very electronegative atom. We also say it's a good Lewis base. When a water molecule and an H2SO4 molecule come near each other, the oxygens in the H2SO4 and the H2O start competing for the electrons in the O-H bonds of both the H2O and the H2SO4 molecules. As it happens, the O in the water wins, because the Os in the H2SO4 have a sulfur atom right next to them, and sulfur has large numbers of electrons to share. So the Os in the H2SO4 molecule aren't quite as "hungry" for electrons.

When the electrons in the O-H bonds transfer their allegiance to the water Os, the bond to the H switches, from the O in the H2SO4 to the O in the H2O. The net result is that now the H is bonded to the water, forming H3O+, and the H2SO4 has one fewer H, so it has turned into HSO4-.

At this point, the competition becomes much more even, and the oxygens in the HSO4- anion are much more likely to keep the remaining electrons in the remaining O-H bond, so this is pretty much where the process stops, although a little bit of HSO4- does react with more H2O to produce more H3O+ and SO4-2.

In short, it is the greater attraction of electrons for the O atom in H2O versus the O atom in H2SO4 that causes the reaction.