Question

Molecular weight of haemoglobin is \(67200 .\) ]f haemoglobin contains \(0.33 \%\) of iron atoms, the number of iron atoms that are present in one molecule of haemoglobin is (At. wt. of iron \(=56\) ) (1) 2 (2) 4 (3) 6 (4) 8

Short answer

The number of iron atoms in haemoglobin is 4.

Step-by-step solution

- Determine the weight of iron in haemoglobin

Haemoglobin contains 0.33% of iron atoms. Therefore, the weight of iron in one molecule of haemoglobin can be calculated as follows: Weight of iron = (0.33/100) * 67200 = 221.76.

- Calculate the number of moles of iron

The atomic weight of iron (Fe) is 56. To find the number of moles of iron in haemoglobin: Number of moles of iron = Weight of iron / Atomic weight of iron = 221.76 / 56 = 3.96.

- Determine the number of iron atoms

Each mole of iron corresponds to one iron atom. Rounding the calculated 3.96 moles to the nearest whole number gives 4 moles. Thus, the number of iron atoms is 4.

Key concepts

molecular weight

Molecular weight is an important concept in chemistry. It refers to the total mass of a molecule and is calculated by summing the atomic weights of all the atoms in the molecule. For example, the molecular weight of haemoglobin is given as 67200. This value is particularly significant because it is used in further calculations to determine properties and quantities of the molecule.
To calculate the molecular weight of a molecule, here are the steps:

• Identify all the atoms in the molecule.
• Find the atomic weights of these atoms, which are often given in a periodic table.
• Multiply the atomic weight of each atom by the number of times that atom appears in the molecule.
• Add up these values to get the molecular weight.

This calculated weight helps understand the molecule’s composition and is fundamental in stoichiometry, which is the calculation of reactants and products in chemical reactions.

haemoglobin

Haemoglobin is a crucial protein found in red blood cells. It carries oxygen from the lungs to the rest of the body and returns carbon dioxide from the body to the lungs. Haemoglobin is complex, with a high molecular weight of 67200. This large molecular size is due to the numerous atoms that make up haemoglobin, including iron atoms, which play a vital role in binding oxygen.
Understanding haemoglobin’s function in the body is vital because:

• It illustrates the role of proteins in biological systems.
• It shows how molecular weight impacts biological activity.
• It highlights the significance of iron in cellular functions.

Knowing the molecular weight and composition of haemoglobin aids in understanding how it operates within the human body and its essential functions in maintaining life.

atomic weight of iron

The atomic weight of an element is the average mass of atoms of an element, measured in atomic mass units (u). For iron (Fe), the atomic weight is 56. This value is used to calculate the number of moles of iron in a given sample. Understanding the atomic weight is crucial because it serves as a fundamental unit in stoichiometry, the aspect of chemistry that deals with quantitative relationships.
For instance, in our exercise, to find out the weight of iron in a molecule of haemoglobin and finally determine the number of iron atoms present, we make use of this constant value for iron.
The steps are:

• Calculate the weight of iron in the molecule using its percentage composition.
• Divide this weight by the atomic weight of iron to get the number of moles.

Therefore, knowing the atomic weight helps in connecting the mass of substances to the number of particles, providing a deeper insight into the structure and behavior of chemicals.

percentage composition

Percentage composition refers to the percentage by mass of each element in a compound. It tells us how much of each element is present in a given mass of the compound. For haemoglobin, it is stated that iron constitutes 0.33% of its weight. This information is useful because it allows calculation of the actual mass of iron in a haemoglobin molecule.
If you have the molecular weight of a compound, you can find the mass of each element by:

• Finding the total molecular weight.
• Using the percentage composition to determine the weight contributed by each element.

In this way, the percentage composition not only gives a clear picture of the element's presence in a compound but also serves as a bridge to calculate moles and atoms, facilitating detailed chemical analysis.

number of moles

The concept of moles is central to understanding chemical quantities. A mole is a unit that measures the amount of a substance. One mole contains exactly Avogadro's number of particles (approximately 6.022 x 10^23). In our exercise, we calculate the number of moles of iron in haemoglobin by dividing the mass of iron by its atomic weight.
The steps involved are:

• Determine the mass of the element (iron in this case).
• Use the formula: Number of moles = Mass / Atomic weight.

For haemoglobin:

• Weight of iron = 221.76 grams (calculated from 0.33% of molecular weight 67200).
• Atomic weight of iron = 56.
• Number of moles of iron = 221.76 / 56 = 3.96, which we round to 4 moles.

Thus, understanding moles helps us translate mass into a countable number of atoms, molecules, or ions, making it easier to analyze and understand chemical reactions.