Question

At which pH is the H₂CO₃/HCO₃^- buffer system most effective? Fill the blank.

The buffer is most effective between (BLANK) (lower pH limit) and (BLANK) (upper pH limit)

Answer 1

Answer) The buffer is most effective between   5.1 (lower pH limit) and 7.1   (upper pH limit)

Explanation :

[Bicarbonate/Carbonic Acid] H2CO3 + H2O <=> H3O+ + HCO3- pKa=6.1 at 37

pH = 6.1 + log[HCO3-]/[H2CO3]

Normally, [HCO3-]=26mmol/L ;
[H2CO3] = 1.3mmol/L in blood
[HCO3-]:[H2CO3] = 20:1
=> Not an effective buffering ratio
=> AND blood pH of 7.4 lies beyond the buffering range, 5.1-7.1 (pKa±1) Phosphates Buffer Conclusion A good buffer has
-high buffer concentration (buffer capacity)
-pKa close to the desired pH

Bicarbonate/carbonic acid buffer: a good buffer when coupled with a healthy respiratory system
Phosphate buffer: an effective buffer in maintaining blood pH at 7.4 but with low buffer capacity Phosphates and bicarbonate are major buffers in our body.
Although phosphate buffer has a pKa of 6.8 which is closer to the blood pH of 7.4, bicarbonate/carbonic acid with pKa of 6.1 is the major buffer system in blood instead of phosphates. Why is carbonate/Carbonic acid a more suitable buffer system in blood? Consider the difference in the concentration of phosphates and bicarbonates in blood. Also, there is usually a higher concentration of bicarbonate than carbonic acid. Question 3 Carbonate/Carbonic acid VS Phosphates Buffer in BLOOD H2CO3 <=> H2O + CO2
H2CO3 is unstable in aqueous solution; some decompose to form H2O and CO2
2 H2O + CO2 <=> H2CO3 + H2O <=> H3O+ + HCO3-
The HCO3-/H2CO3 buffer system coupled with respiratory system to maintain blood pH