Question

Question:An osmotic pressure measurement taken on a solution containinghemoglobin shows that the molar mass of that protein is approximately $\mathbf{65}\mathbf{,}\mathbf{000}\mathbf{}{\mathbf{\text{gmol}}}^{\mathbf{-}\mathbf{1}}$. A chemical analysis shows it to contain 0.344% of iron by mass. How many iron atoms does each hemoglobin molecule contain?

Short answer

Each hemoglobin molecule contains four iron atoms.

Step-by-step solution

Hemoglobin

Hemoglobin is a type of protein which is present in the blood. It has a large amount of iron content in it.

Step 2: Calculation of number of iron atoms in a hemoglobin molecule

It is given that the molar mass of hemoglobin is $65000{\text{gmol}}^{-1}$and it contains $0.344\%$of iron by mass.

Let us consider 1 mol of hemoglobin.

Mass by mass percentage = 0.344%

$\text{Mass}\text{by}\text{mass}\%=\frac{{\text{m}}_{\text{Fe}}}{\text{M}}\times 100$ , where ${\text{m}}_{\text{Fe}}$is the amount of iron, M is the total mass of hemoglobin.

Substituting the values, we get

$0.344=\frac{{\text{m}}_{\text{Fe}}}{\text{65000}}\times 100$

${\text{m}}_{\text{Fe}}=\frac{0.344\times \text{65000}}{100}=223.6\text{g}$

Number of moles of iron, ${\text{n}}_{\text{Fe}}=\frac{{\text{m}}_{\text{Fe}}}{{\text{M}}_{\text{Fe}}}$, ${\text{M}}_{\text{Fe}}$is the molar mass of iron.

Substituting the values, we get

${\text{n}}_{\text{Fe}}=\frac{\text{223.6}\text{g}}{\text{55.845}{\text{gmol}}^{-1}}=4.00\text{mol}$

Now, we can say that one mole of hemoglobin has 4 moles of iron. Hence, each molecule of hemoglobin has four atoms of iron.