Question

Haemoglobin contains 0.33% of Fe by weight. If 1 molecule of haemoglobin contains 2 iron atoms, the molecular weight of haemoglobin will be nearby:
(Atomic weight of Fe = 56)
A. 67000
B. 34000
C. 17000
D. 20000

Answer 1

Hint: For this problem, we have to apply the formula mass per cent which is the ratio of the weight of iron to the molecular weight of the compound. And then the whole formula is multiplied by 100. We have to calculate the weight of the iron also.

Complete Step-by-step answer:
- In the given question, we have to find out the molecular weight of one molecule of haemoglobin which consists of two atoms of iron, among the given options.
- As we know that mass percentage is the formula to determine the percentage of a single element in a given mixture of two or more than two atoms.
- Mass percent is a unitless quantity.
- The formula is given by the ratio of a given weight of iron to the molecular weight of the compound and divided by 100 i.e.
$\text{Mass percent = }\dfrac{\text{Weight of Fe}}{\text{Molecular weight of compound}}\text{ }\times \text{ 100}$
Or $\text{Molecular weight of compound = }\dfrac{\text{Weight of Fe}}{\text{Mass percent}}\text{ }\times \text{ 100}$ ….. (1)
- As we know that it is given that in one molecule of haemoglobin 2 iron atoms are present so the weight of iron will be $2\text{ }\times \text{ 56 = 112g}$.
- Also, it is given that the mass present is 0.33% so putting all the values of in the equation (1) we get
$\text{Molecular weight of compound = }\dfrac{112}{0.33}\text{ }\times \text{ 100}$
The molecular weight of haemoglobin will be 34000.
Therefore, option B is the correct answer.

Note: Haemoglobin is an essential molecule in the human body because it makes all the blood. The red colour of the blood is also due to the presence of haemoglobin. In haemoglobin, there are four subunits, two alpha and two betas.