[warnie]

While determining chromium in carbon steel sample why do we add both H2SO4 and H3PO4 to dissolve the sample?

[Arkcon]

Well, to start a discussion on the options, what other acids do you know of, that you can choose?

[warnie]

I meant why H2SO4 can't serve the purpose alone? Other acid which can be used may be HNO3.

[Arkcon]

Other acid which can be used may be HNO3.

I was waiting for that one.  Bwa-Ha-Ha.  Look up passivation.  If you want to analyze steel samples that contain chromium, and nickel, along with iron, you don't use nitric acid.

[warnie]

Thanks!!!!.But Sir I was actually asked that why H2SO4 alone can't dissolve the sample ,why I need H3PO4 also?

[Arkcon]

Probably a similar reason, that you ,might be able to find, in a metallurgy analytical text.  I'm not an expert on the subject, but I did want to give you a useful hint, to give you something to think about, to try and deduce an answer.  Can you use something yo know about the reactions in the analytical step that might need phosphate present?

[BluRay]

Probably a similar reason, that you ,might be able to find, in a metallurgy analytical text.  I'm not an expert on the subject, but I did want to give you a useful hint, to give you something to think about, to try and deduce an answer.  Can you use something yo know about the reactions in the analytical step that might need phosphate present?

I'm curious about it too. What is the purpose of H₃PO₄?