(Provide custom atomic masses for elements if needed, separated by commas. If blank, standard values will be used.)
Understanding Molar Mass
Molar mass is a fundamental property of a chemical substance. It represents the mass of one mole of that substance and is expressed in grams per mole (g/mol). This value is numerically equal to the atomic mass of an element (in atomic mass units, amu) or the molecular mass of a compound (in amu). The molar mass is crucial for stoichiometric calculations in chemistry, allowing scientists to relate the mass of a substance to the number of moles, and vice versa.
How Molar Mass is Calculated
The molar mass of a compound is determined by summing the molar masses of all the atoms present in its chemical formula. To do this, you need to know:
The chemical formula of the compound (e.g., H₂O for water).
The atomic mass of each element involved. These values are readily available on the periodic table.
The calculation involves multiplying the atomic mass of each element by the number of times that element appears in the chemical formula and then summing these values.
For example, to calculate the molar mass of water (H₂O):
Hydrogen (H): Atomic mass ≈ 1.008 g/mol. There are 2 hydrogen atoms.
Oxygen (O): Atomic mass ≈ 15.999 g/mol. There is 1 oxygen atom.
Molar Mass of H₂O = (2 * Atomic Mass of H) + (1 * Atomic Mass of O)
Molar Mass of H₂O = (2 * 1.008 g/mol) + (1 * 15.999 g/mol)
Molar Mass of H₂O = 2.016 g/mol + 15.999 g/mol
Molar Mass of H₂O = 18.015 g/mol
Using the Calculator
This calculator simplifies the process. Simply enter the chemical formula for the substance you are interested in. For instance, you can enter H2O for water, C6H12O6 for glucose, or NaCl for sodium chloride.
You also have the option to provide custom atomic masses for elements if you are working with specific isotopic compositions or require a higher degree of precision than commonly listed on standard periodic tables. Enter these values in the format ElementSymbol:AtomicMass, ElementSymbol:AtomicMass, for example, H:1.00794, O:15.994915. If this field is left blank, the calculator will use standard atomic masses.
Clicking "Calculate Molar Mass" will display the computed molar mass in g/mol.
Use Cases
The Molar Mass Calculator is a valuable tool for:
Students: Learning general chemistry and performing homework calculations.
Researchers: Quickly calculating molar masses for experiments and publications.
Lab Technicians: Preparing solutions and reagents accurately.
Educators: Demonstrating chemical calculations and principles.
// Standard atomic masses (can be expanded)
var standardAtomicMasses = {
"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, "Ni": 58.693, "Co": 58.933, "Cu": 63.546, "Zn": 65.38,
"Ga": 69.723, "Ge": 72.630, "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": 98.0, "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": 145.0, "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": 209.0, "At": 210.0, "Rn": 222.0
};
function calculateMolarMass() {
var formulaInput = document.getElementById("chemicalFormula");
var customDataInput = document.getElementById("molarMassData");
var resultDiv = document.getElementById("result");
var formula = formulaInput.value.trim();
var customDataString = customDataInput.value.trim();
var totalMolarMass = 0;
var errorMessages = [];
if (!formula) {
resultDiv.innerHTML = "Please enter a chemical formula.";
return;
}
var atomicMasses = standardAtomicMasses;
// Parse custom data if provided
if (customDataString) {
var customEntries = customDataString.split(',');
var parsedCustomMasses = {};
for (var i = 0; i 0) {
parsedCustomMasses[symbol.toUpperCase()] = mass;
} else {
errorMessages.push("Invalid custom mass for '" + symbol + "'.");
}
} else {
errorMessages.push("Invalid custom data format: '" + entry + "'.");
}
}
// Merge custom masses, prioritizing custom ones
atomicMasses = Object.assign({}, standardAtomicMasses, parsedCustomMasses);
}
// Regex to parse the chemical formula
// It looks for an uppercase letter followed by optional lowercase letters (element symbol)
// and then optional numbers (count). It accounts for parentheses for polyatomic ions.
var elementRegex = /([A-Z][a-z]*)(\d*)|(\()|(\))(\d*)/g;
var matches;
var currentFormulaStack = []; // To handle nested parentheses
var currentElementCounts = {}; // Temporary counts for elements within current scope
while ((matches = elementRegex.exec(formula)) !== null) {
if (matches[1] && matches[2] !== undefined) { // Element with count
var elementSymbol = matches[1];
var count = matches[2] ? parseInt(matches[2]) : 1;
if (atomicMasses.hasOwnProperty(elementSymbol)) {
currentElementCounts[elementSymbol] = (currentElementCounts[elementSymbol] || 0) + count;
} else {
errorMessages.push("Element '" + elementSymbol + "' not found in atomic mass data.");
}
} else if (matches[3]) { // Opening parenthesis
currentFormulaStack.push(currentElementCounts); // Save current counts
currentElementCounts = {}; // Reset for new scope
} else if (matches[4] && matches[5] !== undefined) { // Closing parenthesis with count
var count = matches[5] ? parseInt(matches[5]) : 1;
if (currentFormulaStack.length > 0) {
var outerCounts = currentFormulaStack.pop();
// Apply the count to elements within the parenthesis
for (var element in currentElementCounts) {
var value = currentElementCounts[element] * count;
outerCounts[element] = (outerCounts[element] || 0) + value;
}
currentElementCounts = outerCounts; // Restore outer scope counts
} else {
errorMessages.push("Mismatched closing parenthesis found.");
}
}
}
// After parsing, add remaining counts from the outermost scope (if any)
// This handles cases where the entire formula might not be enclosed in implicit outermost parentheses
// For example, if the formula was just 'H2O', currentElementCounts would hold H and O.
if (currentFormulaStack.length > 0) {
errorMessages.push("Mismatched opening parenthesis found.");
}
// Calculate total molar mass from the final element counts
for (var element in currentElementCounts) {
if (atomicMasses.hasOwnProperty(element)) {
totalMolarMass += atomicMasses[element] * currentElementCounts[element];
} else {
// This check is redundant if the parsing logic is correct and already pushed errors
// but kept for safety.
if (!errorMessages.some(msg => msg.includes("Element '" + element + "' not found"))) {
errorMessages.push("Element '" + element + "' not found in atomic mass data.");
}
}
}
if (errorMessages.length > 0) {
resultDiv.innerHTML = errorMessages.join("");
} else if (totalMolarMass > 0) {
resultDiv.innerHTML = totalMolarMass.toFixed(4) + " g/mol";
} else {
resultDiv.innerHTML = "Could not calculate molar mass. Please check input.";
}
}