Molar Mass
Molar mass sums the atomic masses in a formula.
About this topic
Molar mass is the mass of one mole of a substance, in grams per mole (g/mol). It is found by adding the atomic masses of all atoms in the formula: water, H2O, is 2(1.008) + 16.00 = 18.02 g/mol, and sodium chloride is 22.99 + 35.45 = 58.44 g/mol. It is the conversion factor between mass and moles.
The numbers come directly from the periodic table, where each element's atomic mass in atomic mass units is the same number as its molar mass in grams per mole. For compounds, multiply each element's mass by its subscript, including those outside brackets: calcium hydroxide, Ca(OH)2, has 40.08 + 2(16.00 + 1.008) = 74.10 g/mol. The key formulas are moles = mass divided by molar mass, and mass = moles times molar mass.
Worked example: how many moles are in 100 g of calcium carbonate, CaCO3? Molar mass is 40.08 + 12.01 + 3(16.00) = 100.09 g/mol, so there is almost exactly 1.00 mol. Pharmacists, cooks of industrial chemicals, and lab technicians all use molar mass to measure out exact amounts.
Students often forget to multiply by the subscript, use atomic number instead of atomic mass, or confuse molar mass with molecular mass in units. Keep units: g/mol, and round sensibly.
Key ideas
- H₂O = 18 g/mol
- Units g/mol
- Used to convert grams to moles
Quick check
Use cases: where Molar Mass helps
- Homework: review the key idea behind Molar Mass before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Molar Mass without notes.
- Visual learning: play with the interactive lab to see how Molar Mass changes when you adjust its inputs.
- Teaching a friend: explain Molar Mass in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Molar Mass?
Molar mass sums the atomic masses in a formula.
What will I learn in Molar Mass?
H₂O = 18 g/mol. Units g/mol. Used to convert grams to moles.
Is Molar Mass part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Molar Mass lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Molar Mass?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.