Modeling Buffer Systems in the Blood:

Determination of the Buffer Most Resistant to pH Change after the Addition of Carbon Dioxide

Name: Connie Choi

Class: BE 210

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The objective of the experiment is to determine which buffer, carbonic acid, phosphoric acid or a solution with a 1:1 ratio of both, will minimize the pH changes with the addition of carbon dioxide. Also, the buffer capacity ranges of each buffer will be found to see which buffer has a buffer capacity range that best encompasses the pH of the blood (approximately 7.40). It is hypothesized that the phosphoric acid system will have less pH changes than the other buffers when carbon dioxide is added into solution. The formation of bicarbonate would introduce more H⁺ and the H⁺ will react with the weak bases to form H₂CO₃ and H₂PO₄^- depending on the buffer. However, the additional HCO₃^- formed from the carbon dioxide will shift the equilibrium of the carbonic acid buffer H₂CO₃ → H⁺ + HCO₃^-, lowering the pH. In the phosphoric acid buffer, the addition of HCO₃^- does not affect the equilibrium of the buffer. Therefore, the buffer with only phosphoric acid will have the smallest pH changes. The buffer that has a combination of carbonic acid and phosphoric acid will be the second most effective buffer, and also have the largest buffer capacity range because the range includes the buffer capacity ranges of two acids with different pKas. To determine which buffer is most resistant to the addition of dissolved carbon dioxide, the pH of the solution after carbon dioxide has been added will be compared to the buffer without carbon dioxide from the fifth experiment (Refer to figure 1 and figure 2 in the appendix for the titration curve of phosphoric acid).