Molar Mass Calculator
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#molarMassResult {
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Molar Mass Calculator
Chemical Formula:
Enter the chemical formula (case-insensitive, e.g., H2O, CO2).
Calculate Molar Mass
Understanding Molar Mass Calculation
Molar mass is a fundamental property of a chemical substance. It represents the mass of one mole of that substance and is typically expressed in grams per mole (g/mol). Calculating molar mass is crucial in stoichiometry, which is the study of the quantitative relationships between reactants and products in chemical reactions.
To calculate the molar mass of a compound, you need to sum the atomic masses of all the atoms present in its chemical formula. The atomic mass of each element is found on the periodic table.
How to Calculate Molar Mass: Step-by-Step
Identify the Chemical Formula: Obtain the correct chemical formula for the substance you are analyzing. For example, water is H2O, glucose is C6H12O6, and sodium chloride is NaCl.
Count the Atoms: Determine the number of atoms of each element present in one molecule or formula unit of the compound. Subscripts in the chemical formula indicate the number of atoms. If no subscript is present, it means there is only one atom of that element.
For H2O: 2 Hydrogen (H) atoms, 1 Oxygen (O) atom.
For C6H12O6: 6 Carbon (C) atoms, 12 Hydrogen (H) atoms, 6 Oxygen (O) atoms.
For NaCl: 1 Sodium (Na) atom, 1 Chlorine (Cl) atom.
Find Atomic Masses: Look up the atomic mass for each element from the periodic table. Atomic masses are usually given in atomic mass units (amu), but for molar mass calculations, they are directly used in grams per mole (g/mol).
Multiply and Sum: For each element, multiply its atomic mass by the number of atoms of that element in the formula. Then, add up these values for all elements in the compound to get the total molar mass.
Example Calculation: Water (H2O)
Chemical Formula: H2O
Atoms: 2 Hydrogen (H), 1 Oxygen (O)
Atomic Masses (approximate): H = 1.01 g/mol, O = 16.00 g/mol
Calculation:
Hydrogen contribution: 2 atoms * 1.01 g/mol = 2.02 g/mol
Oxygen contribution: 1 atom * 16.00 g/mol = 16.00 g/mol
Total Molar Mass: 2.02 g/mol + 16.00 g/mol = 18.02 g/mol
Example Calculation: Glucose (C6H12O6)
Chemical Formula: C6H12O6
Atoms: 6 Carbon (C), 12 Hydrogen (H), 6 Oxygen (O)
Atomic Masses (approximate): C = 12.01 g/mol, H = 1.01 g/mol, O = 16.00 g/mol
Calculation:
Carbon contribution: 6 atoms * 12.01 g/mol = 72.06 g/mol
Hydrogen contribution: 12 atoms * 1.01 g/mol = 12.12 g/mol
Oxygen contribution: 6 atoms * 16.00 g/mol = 96.00 g/mol
Total Molar Mass: 72.06 g/mol + 12.12 g/mol + 96.00 g/mol = 180.18 g/mol
Common Atomic Masses (g/mol)
Element
Symbol
Atomic Mass (g/mol)
Hydrogen H 1.01 Carbon C 12.01 Nitrogen N 14.01 Oxygen O 16.00 Fluorine F 19.00 Sodium Na 22.99 Magnesium Mg 24.31 Aluminum Al 26.98 Silicon Si 28.09 Phosphorus P 30.97 Sulfur S 32.06 Chlorine Cl 35.45 Potassium K 39.10 Calcium Ca 40.08 Iron Fe 55.85 Copper Cu 63.55 Zinc Zn 65.38 Bromine Br 79.90 Silver Ag 107.87 Iodine I 126.90 Barium Ba 137.33 Gold Au 196.97 Lead Pb 207.2
This calculator automates the process by parsing your chemical formula and using a built-in set of common atomic masses.
// Approximate atomic masses of common elements
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': 39.95, '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': 98.0, '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, 'FR': 223.0, 'RA': 226.0, 'AC': 227.0, 'TH': 232.04,
'PA': 231.04, 'U': 238.03
};
function calculateMolarMass() {
var formulaInput = document.getElementById("chemicalFormula");
var formula = formulaInput.value.trim().toUpperCase(); // Ensure uppercase and remove whitespace
var totalMolarMass = 0;
var formulaError = false;
if (!formula) {
document.getElementById("molarMassResult").innerText = "Invalid Input";
document.getElementById("resultUnits").innerText = "";
return;
}
// Regular expression to find elements and their counts
// It looks for an uppercase letter (element symbol), optionally followed by
// a lowercase letter (for two-letter symbols), and then optionally followed by digits (count).
// Example: H2O -> H2, O1 (O is implicit 1)
// Example: C6H12O6 -> C6, H12, O6
var elementRegex = /([A-Z][a-z]?)(\d*)/g;
var match;
var tempFormula = formula; // Use a temporary variable to avoid issues with regex global flag
while ((match = elementRegex.exec(tempFormula)) !== null) {
var elementSymbol = match[1];
var countStr = match[2];
var count = 1; // Default count is 1
if (countStr) {
count = parseInt(countStr, 10);
}
if (atomicMasses.hasOwnProperty(elementSymbol)) {
var atomicMass = atomicMasses[elementSymbol];
totalMolarMass += atomicMass * count;
} else {
// Element not found in our dictionary
formulaError = true;
break; // Exit loop if an unknown element is found
}
}
// Check if the regex parsed the entire string. If not, it means there's an invalid part.
// For example, "H2O!" would leave "!" unparsed.
if (elementRegex.lastIndex !== formula.length) {
formulaError = true;
}
if (formulaError) {
document.getElementById("molarMassResult").innerText = "Error: Invalid Formula";
document.getElementById("resultUnits").innerText = "";
} else if (totalMolarMass === 0) {
// This can happen if the formula was empty or contained only invalid characters
document.getElementById("molarMassResult").innerText = "Invalid Input";
document.getElementById("resultUnits").innerText = "";
}
else {
// Format to 2 decimal places for typical chemical calculations
document.getElementById("molarMassResult").innerText = totalMolarMass.toFixed(2);
document.getElementById("resultUnits").innerText = "g/mol";
}
}