Problem: The protein hemoglobin (Hb) transports O2 in mammalian blood. Each Hb can bind 4 O2 molecules. The equilibrium constant for the O2-binding reaction is higher in fetal hemoglobin than in adult hemoglobin. In discussing protein oxygen-binding capacity, biochemists use a measure called the  P50 value, defined as the partial pressure of oxygen at which 50% of the protein is saturated. Fetal hemoglobin has a P50 value of 19 torr, and adult hemoglobin has a P50 value of 26.8 torr. Use these data to estimate how much larger Kc is for the aqueous reaction 4 O2(g) + Hb(aq) ⇌ [Hb(O2)4](aq) in a fetus, comparedto Kc for the same reaction in an adult.

FREE Expert Solution

4 O2(g) + Hb(aq) ⇌ [Hb(O2)4](aq)


Kp → equilibrium units in terms of pressure of gaseous species

Kp=productsreactantsKp=1(PO2)4


Fetal hemoglobin:

Pfetal=19 torr×1 atm760 torr

Pfetal = 0.025 atm


Kp, fetal=1(0.025)4

Kp, fetal = 2.56x106


Adult hemoglobin:

Padult=26.8 torr×1 atm760 torr

Padult = 0.035 atm


Kp, adult=1(0.0353)4

Kp, adult = 6.44x105



Kp and Kc are related to one another by the following equation below: 

Kp=KcRTn

R = gas constant = 0.08206 (Latm)/(molK)
T = temperature, K
Δn = moles of gas products – moles of gas reactants


Δn = 0 moles gas – 4 moles gas
Δn = –4 mol


Kp=KcRTnKpRTn=KcRTnRTnKc=KpRTn


T = body temperature = 37°C + 273.15 = 310.15 K

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Problem Details

The protein hemoglobin (Hb) transports O2 in mammalian blood. Each Hb can bind 4 O2 molecules. The equilibrium constant for the O2-binding reaction is higher in fetal hemoglobin than in adult hemoglobin. In discussing protein oxygen-binding capacity, biochemists use a measure called the  P50 value, defined as the partial pressure of oxygen at which 50% of the protein is saturated. Fetal hemoglobin has a P50 value of 19 torr, and adult hemoglobin has a P50 value of 26.8 torr. Use these data to estimate how much larger Kc is for the aqueous reaction 4 O2(g) + Hb(aq) ⇌ [Hb(O2)4](aq) in a fetus, compared
to Kc for the same reaction in an adult.

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