Copper sulphate is prepared by blowing a current of air through copper scrap and dilute $H_2SO_4$. Dilute $HNO_3$ is also added:

• A
  to oxidise copper to $Cu^{2+}$ which then forms $CuSO_4$ with dilute $H_2SO_4$
• B
  to oxidise $Fe^{2+}$ to iron$(III)$ sulphate,which remains in solution after crystallisation of $CuSO_4$
• C
  to speed up the ionisation of $H_2SO_4$ to give $SO_4^{2-}$ ions
• D
  which combines with $H_2SO_4$ to give a very strong oxidising mixture and oxidises $Cu$ to $Cu^{2+}$