[snorkack]

Why is dilute sulphuric acid so nonoxidizing, and allows hydrogen to be reduced?

Standard reduction potentials seem to be:
HSO₄^-+2e^-+3H⁺ H₂SO₃+H₂O +0,16V
H₂SO₃+4e^-+4H⁺ S +3H₂O +0,50V
These 2 both being species applicable in acid conditions, pH 0 meaning H⁺ concentration 1 M, meaning about 10 % H₂SO₄, it follows that SO₂ and H₂SO₃ should dismute in water. The total redox reaction of sulphuric acid ought to be:
HSO₄^-+6e^-+7H⁺ S +4H₂O +0,39V
Strong enough oxidant to oxidize copper, and not allow hydrogen to be reduced.
Next step would be
S+2e^-+2H⁺ H₂ +0,14V
Also, in presence of heavy metals, which form insoluble/stable sulphides, reduction of sulphate to sulphide should be favoured.
If cathode charge is applied to PbSO₄, why should the reaction be
PbSO₄+2e^-+H⁺ Pb+HSO₄^-
rather than
PbSO₄+8e^-+8H⁺ PbS+4H₂O
?

[Hunter2]

Its because sulfur gave all electrons to other atoms here oxigen. It is with +6 in highest oxidation number. Its a very stable one.

[snorkack]

Its because sulfur gave all electrons to other atoms here oxigen. It is with +6 in highest oxidation number. Its a very stable one.

Um? The fact that it´s the highest oxidation number only explains why sulphate is hard to oxidize - sulphur is impossible to oxidize, so it´s oxygen which is oxidized:
2HSO₄^- 2e^-+H₂S₂O₈
But why is reduction of sulphate so hard?
Also, why don´t arrows show properly?

[Borek]

Also, why don´t arrows show properly?

You need to add a space after them.

Actually that's something that should be easy to correct in the forum code, if only I find a free moment to try...

[swintarka]

My guess would be that the activation barrier for reduction of sulfate is very high and that direction should ease you literature research.