Molar mass is a fundamental property of a chemical substance, defined as the mass of one mole of that substance. It is expressed in units of grams per mole (g/mol). This value is numerically equivalent to the substance's atomic mass (in atomic mass units, amu) or molecular mass (in amu), but it represents a macroscopic quantity (one mole).
Calculating the molar mass of a compound is crucial in stoichiometry, a branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions. It allows chemists to determine how much of a substance is needed or produced in a reaction, ensuring accurate and efficient chemical processes.
How to Calculate Molar Mass
The molar mass of a compound is calculated by summing the molar masses of all the atoms present in its chemical formula. You need a periodic table to find the average atomic mass (which is numerically equal to the molar mass) of each element.
For example, to calculate the molar mass of water (H2O):
Find the molar mass of Hydrogen (H) from the periodic table: approximately 1.008 g/mol.
Find the molar mass of Oxygen (O) from the periodic table: approximately 15.999 g/mol.
Multiply the molar mass of each element by the number of atoms of that element in the formula:
For H: 2 atoms * 1.008 g/mol = 2.016 g/mol
For O: 1 atom * 15.999 g/mol = 15.999 g/mol
Sum these values: 2.016 g/mol + 15.999 g/mol = 18.015 g/mol.
Therefore, the molar mass of water is approximately 18.015 g/mol.
Common Use Cases
Stoichiometry: Converting between mass, moles, and volume in chemical reactions.
Solution Preparation: Calculating the mass of solute needed to create a solution of a specific concentration.
Chemical Analysis: Determining the composition of unknown substances.
Research & Development: Designing and optimizing chemical synthesis pathways.
About the Calculator
This calculator simplifies the process of determining molar mass. Simply enter the chemical formula of the substance, and it will calculate the total molar mass based on the atomic masses found in a standard periodic table. It supports chemical formulas with subscripts (e.g., H2O for water) and can handle elements with multiple atoms in their formula.
function calculateMolarMass() {
var formula = document.getElementById("chemicalFormula").value.trim();
var resultElement = document.getElementById("result").getElementsByTagName("span")[0];
resultElement.textContent = "N/A"; // Reset result
if (!formula) {
alert("Please enter a chemical formula.");
return;
}
// Simple periodic table data (simplified for common elements, more can be added)
var atomicMasses = {
"H": 1.008, "He": 4.0026, "Li": 6.94, "Be": 9.0122, "B": 10.81, "C": 12.011, "N": 14.007, "O": 15.999, "F": 18.998, "Ne": 20.180,
"Na": 22.990, "Mg": 24.305, "Al": 26.982, "Si": 28.085, "P": 30.974, "S": 32.06, "Cl": 35.45, "Ar": 39.948,
"K": 39.098, "Ca": 40.078, "Sc": 44.956, "Ti": 47.867, "V": 50.942, "Cr": 51.996, "Mn": 54.938, "Fe": 55.845, "Co": 58.933, "Ni": 58.693, "Cu": 63.546, "Zn": 65.38,
"Ga": 69.723, "Ge": 72.63, "As": 74.922, "Se": 78.971, "Br": 79.904, "Kr": 83.798,
"Rb": 85.468, "Sr": 87.62, "Y": 88.906, "Zr": 91.224, "Nb": 92.906, "Mo": 95.95, "Tc": 98, "Ru": 101.07, "Rh": 102.91, "Pd": 106.42, "Ag": 107.87, "Cd": 112.41, "In": 114.82, "Sn": 118.71, "Sb": 121.76, "Te": 127.60, "I": 126.90, "Xe": 131.29,
"Cs": 132.91, "Ba": 137.33, "La": 138.91, "Ce": 140.12, "Pr": 140.91, "Nd": 144.24, "Pm": 145, "Sm": 150.36, "Eu": 151.96, "Gd": 157.25, "Tb": 158.93, "Dy": 162.50, "Ho": 164.93, "Er": 167.26, "Tm": 168.93, "Yb": 173.05, "Lu": 174.97, "Hf": 178.49, "Ta": 180.95, "W": 183.84, "Re": 186.21, "Os": 190.23, "Ir": 192.22, "Pt": 195.08, "Au": 196.97, "Hg": 200.59, "Tl": 204.38, "Pb": 207.2, "Bi": 208.98, "Po": 209, "At": 210, "Rn": 222,
"Fr": 223, "Ra": 226, "Ac": 227, "Th": 232.04, "Pa": 231.04, "U": 238.03, "Np": 237, "Pu": 244, "Am": 243, "Cm": 247, "Bk": 247, "Cf": 251, "Es": 252, "Fm": 257, "Md": 258, "No": 259, "Lr": 266, "Rf": 267, "Db": 268, "Sg": 269, "Bh": 270, "Hs": 269, "Mt": 278, "Ds": 281, "Rg": 282, "Cn": 285, "Nh": 286, "Fl": 289, "Mc": 290, "Lv": 293, "Ts": 294, "Og": 294
};
var totalMolarMass = 0;
var regex = /([A-Z][a-z]?)(\d*)/g;
var match;
while ((match = regex.exec(formula)) !== null) {
var elementSymbol = match[1];
var count = match[2];
if (atomicMasses[elementSymbol] === undefined) {
alert("Unknown element symbol: " + elementSymbol);
return;
}
var elementMass = atomicMasses[elementSymbol];
var elementCount = parseInt(count) || 1; // Default to 1 if no number is present
totalMolarMass += elementMass * elementCount;
}
if (totalMolarMass > 0) {
// Round to a reasonable number of decimal places for typical chemistry calculations
var roundedMolarMass = totalMolarMass.toFixed(3);
resultElement.textContent = roundedMolarMass;
} else {
resultElement.textContent = "Error";
}
}