Need help with a pH question

here is a better picture

Yes, I can feel your pain ...

It is perfectly feasible for pH to be negative. Any concentration of strong acid greater than 1 will have a negative pH.

In fairness, the pH scale was never designed to work with concentrated acids as one of the basic assumptions - that strong acids are 100% dissociated in aqueous solution does not hold for very strong solutions.

I imagine that they are expecting you to assume 100% dissociation and then blindly apply the pH = -log[H+].

Taking the question at face value, 65% of 1400 = 910g
Moles of nitric acid = 910/63 = 14.44 mol
Hence solution is 14.44 molar in H+ ions = pH -1.16

If we apply equilibrium principles, there is simply not enough water for the full dissociation, assuming:


HNO₃ + H₂O <==> NO₃^- + H₃O⁺

Thanks. When you say 100% dissociation , does that mean h+=hno3 for the concentration ?

Thanks. When you say 100% dissociation , does that mean h+=hno3 for the concentration ?

You might also like to consider what the pH of a very dilute solution of acid might be. For example, nitric acid with a concentration of 10^-9 mol/dm3

Nearly 1?

Remember that [H+][OH-] = 1 x 10^-14

Isn't that kw ? I thought in this case, you will do -log h+ to find pH ... Thanks

Yes, and kw is a CONSTANT

Nearly 1?

Why can't you use pH=-log h + though ? Thanks