Sodium bicarbonate is commonly used in baking, cleaning, and as an antacid.
Understanding Molar Mass
Molar mass is the mass of one mole of a substance (6.022 × 10²³ particles, Avogadro's number). It is expressed in grams per mole (g/mol). For chemical compounds, the molar mass is the sum of the atomic masses of all atoms in the molecular formula.
How to Calculate Molar Mass
1
Write the chemical formula — Identify all elements present and their subscripts (e.g., H₂SO₄ has H×2, S×1, O×4)
2
Find atomic masses — Look up each element's atomic mass from the periodic table (e.g., H = 1.008 g/mol, S = 32.07 g/mol, O = 16.00 g/mol)
3
Multiply by subscripts — Multiply each element's atomic mass by its subscript count in the formula
4
Sum all contributions — Add up the mass contributions of all elements: H: 2×1.008 = 2.016, S: 1×32.07 = 32.07, O: 4×16.00 = 64.00
5
Record the result — The total is the molar mass: 2.016 + 32.07 + 64.00 = 98.09 g/mol
Molar Mass = Σ (Atomic Mass × Subscript) for each element
Sum of all atomic mass contributions in the chemical formula
Handling Special Cases
🔤 Parenthesized Groups
Groups inside parentheses like Ca(OH)₂ have their subscript applied to every element inside. Ca(OH)₂ = Ca × 1, O × 2, H × 2.
💧 Hydrated Compounds
Hydrates use a middle dot (·) like Na₂CO₃·10H₂O. The water molecules are treated separately and added to the total mass.
📐 Percentage Composition
% Element = (Mass contribution of element ÷ Total molar mass) × 100%. This tells you the mass fraction of each element.
⚛️ Significant Figures
Atomic masses are typically given to 4 significant figures. Round final molar mass to 2 decimal places for most practical purposes.
Periodic Table Reference
Common elements with their atomic masses (g/mol):
H
1.008
He
4.003
Li
6.941
Be
9.012
B
10.81
C
12.01
N
14.01
O
16.00
F
19.00
Ne
20.18
Na
22.99
Mg
24.31
Al
26.98
Si
28.09
P
30.97
S
32.07
Cl
35.45
Ar
39.95
K
39.10
Ca
40.08
Sc
44.96
Ti
47.87
V
50.94
Cr
52.00
Mn
54.94
Fe
55.85
Co
58.93
Ni
58.69
Cu
63.55
Zn
65.39
Br
79.90
Ag
107.9
I
126.9
Ba
137.3
Au
197.0
Hg
200.6
Pb
207.2
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Formula Parsing
Smart parser handles element symbols, subscripts, parentheses, and hydrated compounds with the · separator.
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Element Breakdown
See each element's count, atomic mass, total mass contribution, and percentage composition with visual bars.
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Accurate Masses
Uses IUPAC-standard atomic masses for all 118 elements with high precision calculations.
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Educational Guide
Learn how to calculate molar mass step-by-step with examples and a periodic table reference.
Molar mass is a fundamental concept in chemistry that represents the mass of one mole of a substance. One mole is defined as exactly 6.02214076 × 10²³ particles (atoms, molecules, ions, or formula units) — this is known as Avogadro's number. The molar mass of a compound is expressed in grams per mole (g/mol) and is numerically equivalent to the molecular weight of that compound.
The molar mass of any chemical compound is calculated by summing the atomic masses of all atoms present in its chemical formula. For example, water (H₂O) has a molar mass of approximately 18.02 g/mol — consisting of two hydrogen atoms (2 × 1.008 g/mol) and one oxygen atom (16.00 g/mol). This value tells us that one mole of water molecules (about 18 mL of liquid water) has a mass of 18.02 grams.
Understanding molar mass is essential for many chemical calculations, including: converting between mass and moles, preparing solutions of specific concentrations, determining stoichiometric ratios in chemical reactions, calculating empirical and molecular formulas, and analyzing percentage composition of elements within compounds.
Why Molar Mass Matters
Molar mass serves as a bridge between the microscopic world of atoms and molecules and the macroscopic world of grams and kilograms that we can measure in the laboratory. Every chemical reaction is governed by the mole ratios of reactants and products — and molar mass is what allows chemists to convert between the mass of a substance and the number of moles (and therefore the number of molecules) present. Without molar mass, quantitative chemistry would not be possible.
Percentage Composition Explained
The percentage composition of a compound tells you what fraction of the total mass each element contributes. This is calculated as: % Element = (Mass of element in one mole of compound ÷ Molar mass of compound) × 100%. For example, in water (H₂O), hydrogen contributes (2.016 ÷ 18.02) × 100% = 11.2% of the mass, while oxygen contributes (16.00 ÷ 18.02) × 100% = 88.8% of the mass. This information is valuable for determining the empirical formula of a compound from experimental data.
How to Use the Molar Mass Calculator
Using our Molar Mass Calculator is straightforward. Simply type or paste a chemical formula into the input field and click "Calculate Molar Mass." The calculator supports a wide range of chemical notation including:
🔤 Basic Formulas
Simple formulas like H₂O, CO₂, NaCl, H₂SO₄, C₆H₁₂O₆ — just type elements with their subscripts.
📦 Parenthesized Groups
Groups with parentheses: Ca(OH)₂, Mg(NO₃)₂, Al₂(SO₄)₃, Fe₂(CrO₄)₃ — the subscript applies to all atoms inside.
💧 Hydrates
Hydrated compounds: CuSO₄·5H₂O, Na₂CO₃·10H₂O, BaCl₂·2H₂O — use the middle dot (·) to separate the water molecules.
⚛️ Complex Ions
Polyatomic ions like NH₄NO₃, Na₂SO₄, KMnO₄, Ca₃(PO₄)₂ — the parser handles nested structures automatically.
Frequently Asked Questions
What is the difference between molar mass and molecular weight?
Molar mass and molecular weight are often used interchangeably, but there is a subtle difference. Molar mass is the mass of one mole of a substance (expressed in g/mol), while molecular weight (or molecular mass) is the mass of a single molecule (expressed in atomic mass units, amu or Da). Numerically, they are the same value — for example, water has a molecular weight of 18.02 amu and a molar mass of 18.02 g/mol. The distinction is simply one of units and scale.
For ionic compounds like NaCl, the term "formula mass" or "formula weight" is preferred since ionic compounds don't form discrete molecules.
How do I calculate the molar mass of a hydrated compound?
Hydrated compounds contain water molecules bound to their crystal structure. They are written with a middle dot (·) followed by the number of water molecules, like CuSO₄·5H₂O (copper(II) sulfate pentahydrate). To calculate the molar mass:
Step 1: Calculate the molar mass of the anhydrous compound (CuSO₄ = 63.55 + 32.07 + 4 × 16.00 = 159.62 g/mol). Step 2: Calculate the mass of the water molecules (5 × 18.02 = 90.10 g/mol). Step 3: Add them together: 159.62 + 90.10 = 249.72 g/mol.
What elements does the calculator support?
Our Molar Mass Calculator supports all 118 known chemical elements with their most up-to-date IUPAC-standard atomic masses. This includes the common elements (H, C, N, O, Na, Cl, etc.), transition metals (Fe, Cu, Zn, etc.), lanthanides, actinides, and all main group elements. Simply use the correct element symbol (first letter uppercase, second letter lowercase) and the calculator will recognize it.
Why do some elements have decimal atomic masses?
Atomic masses are not whole numbers because they represent the weighted average of all naturally occurring isotopes of an element. For example, chlorine exists as two stable isotopes: chlorine-35 (75.78% abundance) and chlorine-37 (24.22% abundance). The weighted average gives 35.45 g/mol. Similarly, carbon is 98.9% carbon-12 and 1.1% carbon-13, giving an average of 12.01 g/mol. This is why the periodic table shows decimal values rather than simple whole numbers.
How is molar mass used in real-world chemistry?
Molar mass is used throughout chemistry and related fields:
• Stoichiometry: Convert between masses of reactants and products in chemical reactions. • Solution Preparation: Calculate the mass of solute needed to prepare a solution of a given molarity. • Analytical Chemistry: Determine unknown concentrations through titration and gravimetric analysis. • Biochemistry: Calculate the molecular weight of proteins, DNA, and other biomolecules. • Pharmaceuticals: Determine correct dosages and formulation compositions. • Environmental Science: Analyze pollutant concentrations and chemical transformations in the environment.
What is Avogadro's number and how does it relate to molar mass?
Avogadro's number (6.02214076 × 10²³) is the number of particles (atoms, molecules, ions, or formula units) in exactly one mole of a substance. It was named after the Italian scientist Amedeo Avogadro. The relationship between molar mass and Avogadro's number is:
If one molecule of water has a mass of ~18.02 amu, then one mole of water (6.022 × 10²³ molecules) has a mass of 18.02 grams. This is why the numerical value of molar mass in g/mol is the same as the molecular mass in amu — Avogadro's number is the conversion factor between the atomic scale and the macroscopic scale.