How is the molecular weight determined for a molecule?

How is the molecular weight determined for a molecule?

• A. Sum up the atomic weights of each atom in the molecule.
• B. Sum up the osmoles of each atom in a liter.
• C. Multiply the atomic weights of the atoms in the molecule.
• D. Multiply the osmoles of each atom in a liter.

Answer: (A)

Adding the atomic weights of all atoms present in the molecule gives its molecular weight. Each element has a standard atomic weight from the periodic table, and the molecular weight is the sum of those weights for every atom in the molecule. This value also serves as the molar mass when expressed in g/mol, so you can think of it as the mass of one mole of that molecule. For example, water has two hydrogens and one oxygen, so its molecular weight is about 2×1.008 + 15.999 ≈ 18.015 amu, which corresponds to a molar mass of 18.015 g/mol. The other options mix up different concepts: osmoles per liter measure particle concentration in solution, not mass, and multiplying weights or osmoles does not yield a correct molecular weight.

Adding the atomic weights of all atoms present in the molecule gives its molecular weight. Each element has a standard atomic weight from the periodic table, and the molecular weight is the sum of those weights for every atom in the molecule. This value also serves as the molar mass when expressed in g/mol, so you can think of it as the mass of one mole of that molecule. For example, water has two hydrogens and one oxygen, so its molecular weight is about 2×1.008 + 15.999 ≈ 18.015 amu, which corresponds to a molar mass of 18.015 g/mol. The other options mix up different concepts: osmoles per liter measure particle concentration in solution, not mass, and multiplying weights or osmoles does not yield a correct molecular weight.