I have no idea how to start with this problem.
Please teach me step by step in detail.

Here is the probrem;
One of the factors for maintaining blood pH is the ratio of [HCO3-]/[CO2].

Knowing that the sum concentration of biocarbonate and carbon dioxide in blood is 0.0252M and that the pKa for the titration of biocarbonate is 6.1:

a) Find the pH of blood if HCl were added to 0.010M and that all the CO2 produced were to dissolved in the blood.

b) Find the pH of blood if HCl were added to 0.010M and that all the CO2 produced were removed from the system.

The equilibria of carbon dioxide in blood, while conceptually not so difficult, gets numerically messy when you want to plug in specific numbers. There are any number of websites that you can explore depending upon how much detail you want. A "Google" search on terms such as "carbon dioxide bicarbonate equilibria in blood" provides many sites of varying complexity. One such "hit" is: http://www.chemistry.wustl.edu/~edud...er/Buffer.html