Finding chemical equations in a phosphate buffer system

Dear tutor:
I am a better than average Chem student, however, I am stumped on two problems related to 'the phosphate buffer system' and one other concerned with CO2 gas blown through a straw in H2O.

As follows:
1) The phosphate buffer system used in this exercise consists of the phosphate buffer pair known as KH2PO4 & K2HPO. I need to write the chemical equation which occurs when H2SO4 is added to this buffer system.
2) Also, the chemical equation that occurs when NaOH is added to this same 'phosphate buffer system'.
3) If you breathe H2O into a straw the H2O becomes more acidic. How is this represented by an equation? I know it is H2CO3, but does it disassociate into ions in the solution?

Thank you,

Barb

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...O4- will react as an acid and HPO42- as a base. This is illustrated in your problem:

1. Since H2SO4 is a strong acid it will react with a basic component of the buffer i.e. HPO42-. First H2SO4 dissociates:
H2SO4 + 2H2O = 2H3O+ + SO42-

Then:
HPO42- + H3O+ = H2PO4- + H2O

So, the H3O+ ions are removed in the buffer solution.

2. Since NaOH is a strong base, it will react with the acidic component of your buffer, i.e. H2PO4-. Sodium ...