chemistry homework

Question

While drinking a can of Coca-cola, you notice that one of the ingredients is phosphoric acid. The cola has a pH of 3.5. 

What is the hydrogen ion concentration?  

OH- concentration?  

What is the Normality of the phosphoric acid?  N

What is the Molarity of the phosphoric acid?  M

Answer 1

pH = -log [H⁺]

For pH = 3.5, [H⁺] = 1x10^-3.5 = 3.16x10^-4 M

OH^- can be found from [H⁺][OH^-] = Kw = 1x10^-14

[OH^-] = 1x10^-14 / 3.16x10^-4 = 3.16x10^-11 M

Normality of H₃PO₄ = 3 x molarity because of the 3 protons (normality isn't really used much any more)

3.16x10^-4 M H+ x 3 = 9.49x10^-4 N

Can't answer the molarity of H₃PO₄ without knowing the various acid dissociation constants for this acid.