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a) Knowing that the pKa of carbonic acid is 6.37, what is the pH of a buffer that has equal concentrations of carbonic acid and bicarbonate? b) Pre...

a) Knowing that the pKa of carbonic acid is 6.37, what is the pH of a buffer that has equal concentrations of carbonic acid and bicarbonate? b) Predict what should be the necessary proportion of [H2CO3]/[HCO3-] in our blood in order to maintain its pH around 7.4. c) Considering the answer from item b, is the carbonate buffer better for acids or bases? Justify your answer.

a) Calculate the pH of a buffer solution containing equal concentrations of carbonic acid and bicarbonate.
b) Calculate the necessary proportion of [H2CO3]/[HCO3-] in blood to maintain a pH of 7.4.
c) Explain whether the carbonate buffer is better for acids or bases and justify your answer.

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Rogeria Carolino

a) To calculate the pH of a buffer solution with equal concentrations of a weak acid and its conjugate base, you can use the Henderson-Hasselbalch equation:

pH=pKa+log⁡([A−][HA])


pH=pKa+log([HA]


[A−

]

​)

In this case, carbonic acid (H2CO3) is the weak acid, and bicarbonate (HCO3-) is its conjugate base. Given that the pKa of carbonic acid is 6.37, and assuming equal concentrations, the equation simplifies to:

pH=6.37+log⁡(1)=6.37

pH=6.37+log(1)=6.37

Therefore, the pH of the buffer is 6.37.

b) The Henderson-Hasselbalch equation can be rearranged to solve for the ratio of the concentrations:

[H2CO3][HCO3-]=10pH−pKa


[HCO3-]


[H2CO3]

​=10pH−pKa

For a blood pH of 7.4 and a pKa of 6.37:

[H2CO3][HCO3-]=107.4−6.37


[HCO3-]


[H2CO3]

​=107.4−6.37

Calculate this to find the necessary proportion.

c) The carbonate buffer is effective against both acids and bases. This is because it consists of a weak acid (H2CO3

H2CO3) and its conjugate base (HCO3-

HCO3-). The buffer's ability to maintain a stable pH is based on the equilibrium between the weak acid and its conjugate base, allowing it to neutralize both added acids and bases.

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