Question

Hemoglobin, a protein in red blood cells, carries O2 from the lungs to the body's cells. Iron (as ferrous ion, Fe2+) makes up 0.33 mass % of hemoglobin. If the molar mass of hemoglobin is 6.8 × 104 g/mol, how many Fe2+ ions are in one molecule?

Answer 1

Answer: The number of $Fe^{2+}$ ions in one molecule of hemoglobin are 4.

Explanation:

According to mole concept:

1 mole of an element contains $6.022\times 10^{23}$ number of atoms.

We are given:

Mass of 1 mole of hemoglobin = $6.8\times 10^4g$

• Using above equation:

$6.022\times 10^{23}$ number of molecules have a mass of $6.8\times 10^4g$

So, 1 molecule of hemoglobin will have a mass of $\frac{6.8\times 10^4g}{6.022\times 10^{23}}\times 1=1.129\times 10^{-19}g$

It is also given that 0.33 mass % of hemoglobin has $Fe^{2+}$ ions

So, mass of $Fe^{2+}$ ions will be = $\frac{0.33}{100}\times 1.129\times 10^{-19}g=3.7257\times 10^{-22}g$

• To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Given mass of iron ion = $3.7257\times 10^{-22}g$

Molar mass of iron ion = 55.85 g/mol

Putting values in above equation, we get:

$\text{Moles of }Fe^{2+}\text{ ion}=\frac{3.7257\times 10^{-22}g}{55.85g/mol}=6.67\times 10^{-24}mol$

• Using mole concept:

1 mole of an element contains $6.022\times 10^{23}$ number of atoms.

So, $6.67\times 10^{-24}$ moles of hemoglobin will contain = $6.022\times 10^{23}\times 6.67\times 10^{-24}=4$

Hence, the number of $Fe^{2+}$ ions in one molecule of hemoglobin are 4.