Question

The oxygen-carrying protein known as haemoglobin is 0.335% Fe by mass and contains four Fe atoms per haemoglobin molecule. Calculate the molecular weight of this protein.

• A. $66 \,g\, mol^{-1}$
• B. $66.6 \,g\, mol^{-1}$
• C. $6.6683 \times10^4\,g\, mol^{-1}$
• D. $666 \,g\, mol^{-1}$

Answer 1

Answer: (C)

Percentage by mass of Fe in haemoglobin is 0.335%.
So, $\frac{4\times At\, wt \,of\, Fe}{Mol \,wt\, of\, haemoglobin}\times100=\%\,Fe$
or $\frac{4\times55.847}{Mol \,wt\, of\, haemoglobin}\times100=0.335$
or Mol. wt. of haemoglobin $=\frac{400\times55.847}{0.335}=66683\,g\,mol^{-1}$