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Instantly compute the molar mass of any compound and see a detailed breakdown of its elemental mass percentages. Save time balancing your equations.
Last updated: March 3, 2026
(NH4)2SO4Remember to use correct capitalization. Formulas are case-sensitive to differentiate elements. For instance, Co represents Cobalt, while CO means Carbon Monoxide.
| Element | Atoms | Mass (g) | Percent |
|---|---|---|---|
O | 1 | 15.999 | 88.81% |
H | 2 | 2.016 | 11.19% |
Chemical compounds are combinations of different elements. A molecular weight calculation simply counts the combined weight of every atom in the molecule.
Grams per mole (g/mol) provides a bridge between two worlds: the microscopic world of atoms and the macroscopic world of laboratory scales. Because a single atom weighs practically nothing, chemists measure them in "moles" (groups of ~6.022 × 10²³ atoms).
Looking at the periodic table, Carbon has an atomic mass of ~12. That means one mole of Carbon weighs exactly 12 grams.
Whenever you see parenthesis in a chemical formula followed by a number, that number is a multiplier for everything inside.
Molecular weight (also called molar mass) tells you how heavy one mole of a compound is, usually in g/mol. It is a foundational step for chemistry problems like balancing equations, converting between grams and moles, and calculating mass percent composition for lab reporting.
To compute molar mass, you multiply each element's atomic mass by how many atoms of that element appear in the chemical formula, then sum everything up:
Atomic Mass
The periodic-table value for each element (in amu, numerically equal to g/mol).
Atom Count
Directly read from subscripts (e.g., H2) or expanded using parentheses multipliers (e.g., (SO4)2).
Sum All Contributions
Add each element's total mass contribution to get the compound's molar mass.
Mass percent tells you what fraction of the compound's total molar mass comes from each element. For an element X:
This is especially useful when analyzing formulas like salts, acids, and hydrates where lab results are reported in composition terms.
H: 2 × 1.008 = 2.016
O: 1 × 15.999 = 15.999
Molar mass ≈ 18.015 g/mol
N: 2 × 14.007 = 28.014
H: 8 × 1.008 = 8.064
S: 1 × 32.06 = 32.06
O: 4 × 15.999 = 63.996
Molar mass ≈ 132.134 g/mol
C: 6 × 12.011 = 72.066
H: 12 × 1.008 = 12.096
O: 6 × 15.999 = 95.994
Molar mass ≈ 180.156 g/mol
Total ≈ 18.015 g/mol. Hydrogen mass contribution ≈ 2.016 g, so H ≈ 11.2% and oxygen contribution ≈ 15.999 g, so O ≈ 88.8%.
Use this table as a quick mental guide for how molar mass is used across common chemistry contexts.
| Compound Type | Common Examples | Typical Molar Mass (g/mol) | Most Common Use |
|---|---|---|---|
| Small molecules | H2O, CO2, NH3 | ~10 to 60 | Stoichiometry & unit conversion |
| Salts & ionic compounds | (NH4)2SO4, NaCl | ~50 to 300 | Mass percent composition & lab calculations |
| Hydrates | CuSO4·5H2O | Varies widely | Moisture content & formula interpretation |
| Larger organics | C6H12O6, CH3COOH | ~60 to 250 | Reaction amounts & concentration conversions |
Help your classmates save time making calculations for titration and compound balancing homework.
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