Molecular Weight

Molecular weight is a measure of the mass of a molecule. It is calculated by summing the atomic weights of all the atoms in a molecule. The molecular weight is expressed in atomic mass units (amu) or in grams per mole (g/mol).

Calculating Molecular Weight

To calculate the molecular weight of a molecule, you need to know the chemical formula of the molecule. For example, let's calculate the molecular weight of glucose (C6H12O6):

1. Find the atomic weights of each element in the molecule. The atomic weight of carbon (C) is 12.01 amu, hydrogen (H) is 1.008 amu, and oxygen (O) is 16.00 amu.
2. Multiply the atomic weight of each element by the number of atoms of that element in the molecule. In the case of glucose, there are 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.
3. Add up the products from step 2 to get the molecular weight:
   • (6 * 12.01 amu) + (12 * 1.008 amu) + (6 * 16.00 amu) = 72.06 amu + 12.096 amu + 96.00 amu = 180.156 amu

So, the molecular weight of glucose is 180.156 amu or 180.156 g/mol.

Significance of Molecular Weight

Molecular weight is important in various fields of science, especially in chemistry and biochemistry. It is used to determine the amount of a substance needed for a reaction, to calculate the concentration of a solution, and to understand the physical and chemical properties of a compound.

Practice Questions

1. Calculate the molecular weight of water (H2O).
2. Why is molecular weight important in biological research?
3. Explain how molecular weight is used in determining the concentration of a solution.