Molar Mass Calculator

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Molar Mass Calculator

Calculate the molar mass (molecular weight) of any chemical compound by entering its molecular formula.

Chemical Formula

Use standard element symbols. Parentheses supported. Case-sensitive (e.g. Co not CO).

Calculate Molar Mass Enter a formula above and click Calculate.

const MOL_WEIGHTS = { H:1.008,He:4.0026,Li:6.941,Be:9.0122,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:95.96,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:262,Rf:267,Db:268,Sg:271,Bh:272,Hs:270, Mt:276,Ds:281,Rg:280,Cn:285,Nh:284,Fl:289,Mc:288,Lv:293,Ts:294,Og:294 };

function molParseFormula(formula) { // Recursive parser: returns {element: count, ...} function parseAt(str, pos) { let counts = {}; while (pos = '0' && str[pos] = 'A' && str[pos] = 'a' && str[pos] = '0' && str[pos] = '0' && str[pos] Please enter a chemical formula.'; return; }

// Basic validation: only allowed characters if (!/^[A-Za-z0-9()[]]+$/.test(formulaInput)) { resultDiv.innerHTML = 'Invalid characters in formula. Use letters, digits, and parentheses only.'; return; }

let counts; try { counts = molParseFormula(formulaInput); } catch(e) { resultDiv.innerHTML = 'Parse error: ' + e.message + ''; return; }

if (Object.keys(counts).length === 0) { resultDiv.innerHTML = 'No elements found in formula.'; return; }

// Check all elements are known let unknownEls = []; for (let el in counts) { if (!(el in MOL_WEIGHTS)) unknownEls.push(el); } if (unknownEls.length > 0) { resultDiv.innerHTML = 'Unknown element symbol(s): ' + unknownEls.join(', ') + '. Check capitalisation (e.g. use Co for cobalt, not CO).'; return; }

// Calculate molar mass let totalMass = 0; let breakdown = []; // Sort elements: C first, H second, then alphabetical (Hill system) let elements = Object.keys(counts); let sorted = []; if (elements.includes('C')) { sorted.push('C'); elements = elements.filter(e => e !== 'C'); } if (elements.includes('H')) { sorted.push('H'); elements = elements.filter(e => e !== 'H'); } elements.sort(); sorted = sorted.concat(elements);

for (let el of sorted) { let n = counts[el]; let w = MOL_WEIGHTS[el]; let contrib = n * w; totalMass += contrib; breakdown.push({el, n, w, contrib}); }

// Build breakdown table let rows = breakdown.map(b => '' + b.el + '' + b.n + '' + b.w.toFixed(4) + '' + b.contrib.toFixed(4) + '' ).join('');

resultDiv.innerHTML = 'Molar Mass of ' + formulaInput + ' = ' + totalMass.toFixed(4) + ' g/mol' + '' + '' + 'Element' + 'Count' + 'Atomic Mass (g/mol)' + 'Contribution (g/mol)' + '' + rows + '' + '' + 'Total Molar Mass' + '' + totalMass.toFixed(4) + ' g/mol' + ''; }

document.getElementById('mol-formula').addEventListener('keydown', function(e) { if (e.key === 'Enter') molCalc(); });

#### Formula

Molar Mass (M) = Σ (ni × Ai)

Where ni is the number of atoms of element i in the formula unit, and Ai is the standard atomic weight of element i in g/mol. The result is expressed in grams per mole (g/mol), also written as Da (daltons) or u (unified atomic mass units) for a single molecule.

Elements are listed using the Hill system: carbon first, hydrogen second, then all remaining elements alphabetically.

#### Assumptions & References

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