Molar mass is a fundamental property of a chemical substance, defined as the mass of one mole of that substance. It is expressed in grams per mole (g/mol). Calculating the molar mass of a compound is essential in stoichiometry, allowing chemists to relate the mass of a substance to the number of moles, and vice versa. This is crucial for predicting product yields, determining reactant quantities, and understanding reaction proportions.
The molar mass of a compound is calculated by summing the molar masses of all the atoms present in its chemical formula. To do this, you need to:
Identify the Elements: Determine all the unique chemical elements present in the formula.
Count the Atoms: For each element, count the number of atoms indicated by its subscript in the chemical formula. If there is no subscript, it implies one atom of that element.
Find Atomic Masses: Consult a periodic table to find the atomic mass (also known as the atomic weight) of each element. These values are typically found in atomic mass units (amu) but are numerically equivalent to molar mass in grams per mole (g/mol).
Calculate Total Mass: Multiply the atomic mass of each element by the number of atoms of that element in the formula.
Sum the Masses: Add up the masses calculated in the previous step for all elements in the compound. The resulting sum is the molar mass of the compound in g/mol.
Example: Calculating the Molar Mass of Sulfuric Acid (H₂SO₄)
Let's calculate the molar mass of sulfuric acid (H₂SO₄):
Hydrogen (H): There are 2 hydrogen atoms. The atomic mass of Hydrogen is approximately 1.008 g/mol.
Calculation: 2 * 1.008 g/mol = 2.016 g/mol
Sulfur (S): There is 1 sulfur atom. The atomic mass of Sulfur is approximately 32.06 g/mol.
Calculation: 1 * 32.06 g/mol = 32.06 g/mol
Oxygen (O): There are 4 oxygen atoms. The atomic mass of Oxygen is approximately 16.00 g/mol.
Calculation: 4 * 16.00 g/mol = 64.00 g/mol
This calculator automates this process. Simply enter the chemical formula, and it will parse the elements and their counts to provide the molar mass. Note that for complex formulas with parentheses (e.g., Ca(OH)₂), this simple calculator may need further refinement. However, it handles common formulas effectively.
// Atomic masses (approximated for common elements)
var atomicMasses = {
'H': 1.008, 'He': 4.003, 'Li': 6.941, 'Be': 9.012, 'B': 10.811,
'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': 28.086, 'P': 30.974,
'S': 32.065, 'Cl': 35.453, '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': 72.630, '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': 102.905,
'Pd': 106.42, 'Ag': 107.868, 'Cd': 112.414, 'In': 114.818, 'Sn': 118.710,
'Sb': 121.760, 'Te': 127.60, 'I': 126.904, 'Xe': 131.293, 'Cs': 132.905,
'Ba': 137.327, 'La': 138.905, 'Ce': 140.116, 'Pr': 140.908, 'Nd': 144.242,
'Pm': 145.0, 'Sm': 150.36, 'Eu': 151.964, 'Gd': 157.25, 'Tb': 158.925,
'Dy': 162.500, 'Ho': 164.930, 'Er': 167.259, 'Tm': 168.934, 'Yb': 173.054,
'Lu': 174.966, 'Hf': 178.49, 'Ta': 180.948, 'W': 183.84, 'Re': 186.207,
'Os': 190.23, 'Ir': 192.217, 'Pt': 195.084, 'Au': 196.967, 'Hg': 200.59,
'Tl': 204.383, 'Pb': 207.2, 'Bi': 208.980, 'Po': 209.0, 'At': 210.0,
'Rn': 222.0, 'Fr': 223.0, 'Ra': 226.0, 'Ac': 227.0, 'Th': 232.038,
'Pa': 231.036, 'U': 238.029, 'Np': 237.0, 'Pu': 244.0, 'Am': 243.0,
'Cm': 247.0, 'Bk': 247.0, 'Cf': 251.0, 'Es': 252.0, 'Fm': 257.0,
'Md': 258.0, 'No': 259.0, 'Lr': 266.0, 'Rf': 267.0, 'Db': 268.0,
'Sg': 269.0, 'Bh': 270.0, 'Hs': 269.0, 'Mt': 278.0, 'Ds': 281.0,
'Rg': 282.0, 'Cn': 285.0, 'Nh': 286.0, 'Fl': 289.0, 'Mc': 290.0,
'Lv': 293.0, 'Ts': 294.0, 'Og': 294.0
};
function calculateMolarMass() {
var formulaInput = document.getElementById("chemicalFormula").value.trim();
var resultDiv = document.getElementById("result").querySelector("span");
if (!formulaInput) {
resultDiv.textContent = "N/A";
return;
}
var molarMass = 0;
var regex = /([A-Z][a-z]*)(\d*)/g;
var match;
// Basic parsing for simple formulas. Handles element followed by optional number.
// Does NOT handle parentheses or complex nested structures.
while ((match = regex.exec(formulaInput)) !== null) {
var element = match[1];
var countStr = match[2];
var count = countStr === " ? 1 : parseInt(countStr, 10);
if (isNaN(count)) {
// This case should ideally not be hit with the regex, but as a safeguard
resultDiv.textContent = "Invalid Formula";
return;
}
if (atomicMasses.hasOwnProperty(element)) {
molarMass += atomicMasses[element] * count;
} else {
resultDiv.textContent = "Unknown Element";
return;
}
}
// Check if any part of the formula was parsed correctly
// If the loop ran but molarMass is still 0 and formula wasn't empty,
// it might indicate an issue with formula format not caught by regex.
if (molarMass === 0 && formulaInput !== "") {
resultDiv.textContent = "Invalid Format";
return;
}
resultDiv.textContent = molarMass.toFixed(3); // Display with 3 decimal places
}