Question

The pH of blood depends on the [HCO3-/H2CO3] balance. ([H2CO3] is equal to the amount of dissolved CO2). Calculate the bicarbonate (HCO3-) : carbon dioxide ratio for a normal blood pH of 7.40. (the pKa1 of carbonic acid is 6.10 at 37oC, body temperature). (A) 20 : 1 (B) 1.3 :1 (C) 2 : 1 (D) 1 : 20 (E) 1 : 0.01

Answer 1

Answer: Option (A) is the correct answer.

Step-by-step explanation:

The given data is as follows.

pH = 7.40,
`[H_(2)CO_(3)]` =
`[CO_(2)]`

`pK_(a)` = 6.10

We have to find
`\frac{[HCO_^(-){3}]}{[CO_(2)]}` = ?

According to Henderson-Hasselbalch equation,

pH =
`pK_(a) + log_(10) ([Salt])/([Acid])`

Hence, putting the given values into the above equation as follows.

pH =
`pK_(a) + log_(10) ([Salt])/([Acid])`

or, pH =
`pK_(a) + log_(10) ([HCO^(-)_(3)])/([H_(2)CO_(3)])`

7.40 = 6.10 +
`log_(10) ([HCO^(-)_(3)])/([H_(2)CO_(3)])`

`log_(10) ([HCO^(-)_(3)])/([H_(2)CO_(3)])` = 1.30

`([HCO^(-)_(3)])/([H_(2)CO_(3)])` = antilog (1.30)

= 20

Since, it is given that
`[H_(2)CO_(3)]` =
`[CO_(2)]`.

Therefore,
`([HCO^(-)_(3)])/([H_(2)CO_(3)])` or
`([HCO^(-)_(3)])/([CO_(2)])` =
`(20)/(1)`

Thus, we can conclude that the bicarbonate (HCO3-) : carbon dioxide ratio for a normal blood pH of 7.40 is 20:1.