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Molar Mass Calculator
Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is the cornerstone of stoichiometric calculations, allowing you to convert between mass and amount of substance. This calculator determines the molar mass of a compound from element symbols and atom counts. It supports three modes: calculating molar mass alone, finding the number of moles from a sample mass (n = m / M), and computing the mass for a given number of moles (m = n × M). The tool is ideal for chemistry students, teachers and laboratory professionals.
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How the molar mass calculator works
The calculator supports three calculation modes: • Molar mass mode: enter element symbols (e.g. H, O, C, N) and atom counts. The calculator sums atomic mass × atom count for each element and returns the result in g/mol. • Moles mode (n = m / M): enter the compound composition and sample mass in grams. The calculator returns n = m / M. • Mass mode (m = n × M): enter the compound composition and number of moles. The calculator returns the mass m = n × M in grams. The atomic mass table covers 27 elements. Unknown symbols are silently ignored. All results are rounded to 4 significant figures.
Example: water H₂O and sodium chloride NaCl
Water H₂O: H=2, O=1 M = 2 × 1.008 + 1 × 15.999 = 18.015 g/mol Sodium chloride NaCl: Na=1, Cl=1 M = 22.990 + 35.453 = 58.443 g/mol Carbon dioxide CO₂: C=1, O=2 M = 12.011 + 2 × 15.999 = 44.009 g/mol Moles mode example: 36 g of H₂O, M = 18.015 g/mol → n = 36 / 18.015 ≈ 2 mol Mass mode example: 3 moles of NaCl, M = 58.443 g/mol → m = 3 × 58.443 = 175.3 g
Frequently asked questions
What is molar mass?
Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). Numerically it equals the atomic or molecular mass expressed in atomic mass units (u). Example: the molar mass of water H₂O is approximately 18.015 g/mol.
How do I calculate the molar mass of a chemical compound?
Sum the atomic masses of all elements multiplied by their atom counts: M = Σ(nᵢ × Mᵢ). Example: M(CO₂) = 12.011 + 2 × 15.999 = 44.009 g/mol.
What is a mole and what is Avogadro's number?
A mole is the SI base unit of amount of substance. One mole contains exactly 6.02214076 × 10²³ particles — this is Avogadro's number (Nₐ). Example: 1 mole of water H₂O weighs 18.015 g and contains 6.022 × 10²³ molecules.
How do I calculate the number of moles from mass and molar mass?
Use the formula n = m / M, where m is the mass in grams and M is the molar mass in g/mol. Example: 36 g of water (M = 18.015 g/mol) gives n = 36 / 18.015 ≈ 2 mol.
How do I calculate the mass of a substance from the number of moles?
Use the formula m = n × M. Example: 3 moles of NaCl (M = 58.443 g/mol) weigh m = 3 × 58.443 = 175.3 g.
What are the atomic masses of the most common elements?
Common atomic masses: H = 1.008; C = 12.011; N = 14.007; O = 15.999; Na = 22.990; Mg = 24.305; S = 32.065; Cl = 35.453; Ca = 40.078; Fe = 55.845; Cu = 63.546. Values are from IUPAC tables.
Why is molar mass important in chemistry?
Molar mass is essential in stoichiometry — it converts between mass and amount of substance. It is used to calculate solution concentrations, reactant and product quantities in chemical reactions, and to interpret analytical laboratory results.
What is the difference between molar mass and molecular mass?
Molecular mass (relative molecular mass) is dimensionless and expressed in atomic mass units (u or Da). Molar mass is expressed in g/mol. Numerically they are equal: the molecular mass of water is 18.015 u, and its molar mass is 18.015 g/mol.
How do I use the molar mass calculator?
Choose the mode: 'Calculate molar mass' — enter element symbols and atom counts (e.g. H=2, O=1 for water H₂O); 'Calculate moles' — enter composition and sample mass in grams; 'Calculate mass' — enter composition and number of moles. The calculator accepts up to 5 different elements.
How many elements does the calculator support?
The calculator handles up to 5 different elements per compound and includes a table of 27 common elements: H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, K, Ca, Fe, Cu, Zn, Br, Ag, I, Au, Pb. Unrecognised symbols are silently ignored.
This calculator is for educational purposes. Atomic masses are sourced from IUPAC tables and rounded to three decimal places. Results may differ slightly from the most current IUPAC values.
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