Molecular Weight Calculator
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Molecular Weight Calculator
Enter the chemical formula for the substance. You can use standard element symbols and numbers for subscripts. For example: H2O, C6H12O6, NaCl.
Chemical Formula:
Calculate Molecular Weight
Understanding Molecular Weight
The Molecular Weight (also known as molar mass) of a chemical compound is the sum of the atomic weights of all atoms in one molecule of that compound. It is typically expressed in grams per mole (g/mol). This value is crucial in stoichiometry, analytical chemistry, and various other scientific fields for quantifying substances and predicting reaction outcomes.
To calculate the molecular weight, we need a reference table of atomic weights for each element. These atomic weights are based on the average mass of isotopes of an element, weighted by their natural abundance.
How it Works:
1. Identify Elements and Counts: The chemical formula is parsed to identify each unique element present and the number of atoms of that element in the molecule. For example, in water (H₂O), there are two Hydrogen (H) atoms and one Oxygen (O) atom.
2. Look Up Atomic Weights: The standard atomic weight for each identified element is retrieved from a reliable source (like the IUPAC periodic table).
3. Calculate Total Weight: For each element, multiply its atomic weight by the number of atoms of that element in the molecule.
4. Sum Results: Add up the contributions from all elements to get the total molecular weight of the compound.
Example Calculation (Water – H₂O):
Atomic Weight of Hydrogen (H) ≈ 1.008 g/mol
Calculation:
18.015 g/mol
Example Calculation (Glucose – C₆H₁₂O₆):
Atomic Weight of Carbon (C) ≈ 12.011 g/mol
Calculation:
180.156 g/mol
Use Cases:
Stoichiometry: Determining reactant and product quantities in chemical reactions.Solution Preparation: Calculating the mass needed to achieve a desired molar concentration.Analytical Techniques: Interpreting mass spectrometry data and other analytical results.Chemical Engineering: Designing and optimizing chemical processes.
// Atomic weights (approximate values, sufficient for most common calculations)
var atomicWeights = {
"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": 102.906, "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": 131.294,
"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 calculateMolecularWeight() {
var formulaInput = document.getElementById("chemicalFormula").value.trim();
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous result
if (!formulaInput) {
resultDiv.innerHTML = "Please enter a chemical formula.";
resultDiv.style.backgroundColor = "#ffc107"; // Warning yellow
return;
}
var totalWeight = 0;
var parsedFormula = parseFormula(formulaInput);
if (parsedFormula === null) {
resultDiv.innerHTML = "Invalid formula format. Please use standard element symbols and numbers (e.g., H2O, C6H12O6).";
resultDiv.style.backgroundColor = "#dc3545"; // Error red
return;
}
for (var element in parsedFormula) {
if (atomicWeights.hasOwnProperty(element)) {
totalWeight += atomicWeights[element] * parsedFormula[element];
} else {
resultDiv.innerHTML = "Unknown element '" + element + "' found in formula.";
resultDiv.style.backgroundColor = "#dc3545″; // Error red
return;
}
}
if (totalWeight > 0) {
resultDiv.innerHTML = totalWeight.toFixed(3) + " g/mol";
resultDiv.innerHTML += "
(grams per mole) ";
resultDiv.style.backgroundColor = "var(–success-green)";
} else if (Object.keys(parsedFormula).length === 0 && formulaInput.length > 0) {
resultDiv.innerHTML = "Could not parse the formula. Ensure correct formatting.";
resultDiv.style.backgroundColor = "#dc3545"; // Error red
}
}
function parseFormula(formula) {
var parsed = {};
var regex = /([A-Z][a-z]*)(\d*)/g;
var match;
var lastIndex = 0;
while ((match = regex.exec(formula)) !== null) {
// Check if the regex matched something unexpected at the beginning
if (match.index > lastIndex) {
return null; // Invalid characters found before the first element
}
var element = match[1];
var countStr = match[2];
var count = countStr === "" ? 1 : parseInt(countStr, 10);
if (isNaN(count)) {
return null; // Should not happen with the regex, but good for safety
}
if (parsed.hasOwnProperty(element)) {
parsed[element] += count;
} else {
parsed[element] = count;
}
lastIndex = regex.lastIndex;
}
// Check if the entire string was consumed by the regex matches
if (lastIndex !== formula.length) {
return null; // Trailing invalid characters or incomplete parse
}
// Handle cases where the input was empty or only contained invalid characters
if (Object.keys(parsed).length === 0 && formula.length > 0) {
return null;
}
return parsed;
}