Question 1

What is molecular weight?

Accepted Answer

Molecular weight (also called molar mass) is the sum of the atomic masses of all atoms in a molecule, expressed in grams per mole (g/mol). It tells you how much one mole (6.022 × 10²³ particles) of the substance weighs.

Question 2

How do I calculate molecular weight from a formula?

Accepted Answer

Multiply each element's atomic mass by its subscript (number of atoms), then add all the results. For example, H₂O = 2(1.008) + 1(15.999) = 18.015 g/mol.

Question 3

What is the difference between molecular weight and formula weight?

Accepted Answer

Molecular weight applies to covalent (molecular) compounds, while formula weight applies to ionic compounds like NaCl that do not form discrete molecules. The calculation method is the same for both.

Question 4

Where do I find atomic masses?

Accepted Answer

Atomic masses are listed on the periodic table. They are weighted averages of all natural isotopes of each element. For example, carbon's atomic mass is 12.011 g/mol, not exactly 12, because it includes small amounts of carbon-13.

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