[angst]

I have to prepare a H₃PO₄ + H₂SO₄ mixture, I have the method to make this mixture but I would like to know the ratio of this mixture, can somebody help me i this??

Mix 100ml of 85% of H₃PO₄ + 100 ml 96% H₂SO₄ then add in 400 ml of distilled water.

What is the purpose of this mixture?? ( determination of total Fe2+ in pickling solution)

Thanks.