Question

Myoglobin stores oxygen for metabolic process in muscle. Chemical analysis shows that it contains 0.32% Fe by mass. If there is one Fe atom per molecule of myoglobin, what is the molar mass of myoglobin? [At. Mass of Fe = 56 u]

• A. 1.75 × 104 g/mol
• B. 3.5 × 105 g/mol
• C. 1× 104 g/mol
• D. 2.5 × 105 g/mol

Answer 1

Answer: (A)

1.75 × 104 g/mol

Answer 2

Given that myoglobin contains 0.32% Fe by mass and has one Fe atom per molecule,

The mass contribution of Fe is:

$$\text{Mass contribution of Fe} = 56\ \text{g/mol}$$

Let the molar mass of myoglobin be $M$. Then,

$$0.0032 \times M = 56 \quad \Rightarrow \quad M = \frac{56}{0.0032} = 1.75 \times 10^4\ \text{g/mol}$$