Grams to Moles Calculator
Convert between grams and moles for any chemical substance. Choose a common compound or enter a custom molar mass.
⚖️ Grams ↔ Moles Converter
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What Is a Mole?
A mole (symbol: mol) is the SI unit of amount of substance. One mole contains exactly 6.02214076 × 1023 elementary entities (atoms, molecules, ions, etc.). This number is known as Avogadro's number (NA).
The mole concept provides a bridge between the atomic scale and the macroscopic scale. While individual atoms and molecules are far too small to count directly, the mole allows chemists to work with practical quantities — grams of material — while knowing exactly how many particles are involved.
Grams to Moles Formula
The conversion between grams and moles is straightforward:
Where:
- n — Number of moles (mol)
- m — Mass of the substance (g)
- M — Molar mass of the substance (g/mol)
To convert in the reverse direction (moles to grams):
What Is Molar Mass?
The molar mass of a substance is the mass of one mole of that substance, expressed in grams per mole (g/mol). For elements, the molar mass is numerically equal to the atomic mass listed on the periodic table. For compounds, the molar mass is the sum of the atomic masses of all atoms in the formula.
Water has 2 hydrogen atoms and 1 oxygen atom:
M = 2 × 1.008 + 1 × 15.999 = 2.016 + 15.999 = 18.015 g/mol
How to Convert Grams to Moles
- Measure the mass of your sample in grams.
- Find the molar mass of the substance. For elements, use the periodic table. For compounds, add up all atomic masses in the chemical formula.
- Divide the mass by the molar mass: n = m / M.
Step 1: Mass = 100 g
Step 2: Molar mass of H2O = 18.015 g/mol
Step 3: n = 100 / 18.015 = 5.551 mol
This means 100 g of water contains 5.551 moles, or about 3.34 × 1024 water molecules.
Common Molar Masses
| Substance | Formula | Molar Mass (g/mol) |
|---|---|---|
| Water | H2O | 18.015 |
| Carbon Dioxide | CO2 | 44.009 |
| Sodium Chloride | NaCl | 58.44 |
| Glucose | C6H12O6 | 180.16 |
| Sulfuric Acid | H2SO4 | 98.079 |
| Sodium Hydroxide | NaOH | 40.00 |
| Ethanol | C2H5OH | 46.068 |
| Ammonia | NH3 | 17.031 |
| Calcium Carbonate | CaCO3 | 100.09 |
| Iron(III) Oxide | Fe2O3 | 159.69 |
Moles to Number of Particles
Once you know the number of moles, you can find the number of individual particles:
Why Are Moles Important in Chemistry?
- Stoichiometry: Chemical equations are balanced in terms of moles, not grams. Moles let you determine exactly how much of each reagent is needed and how much product will form.
- Solution preparation: Molarity (M) is defined as moles of solute per liter of solution. To prepare solutions, you must convert between grams and moles.
- Gas calculations: The ideal gas law (PV = nRT) uses moles. At STP, one mole of any ideal gas occupies 22.414 liters.
- Comparative analysis: Moles allow meaningful comparison between substances of different molecular weights.
Frequently Asked Questions
How many grams are in one mole?
This depends entirely on the substance. One mole of hydrogen gas (H2) has a mass of 2.016 g, while one mole of uranium (U) has a mass of 238.03 g. The mass of one mole is numerically equal to the molar mass in g/mol.
How do I find the molar mass of a compound?
Write the chemical formula, look up each element's atomic mass on the periodic table, multiply by the number of atoms of each element, and add them all together. For example, for Ca(OH)2: Ca (40.08) + 2 × O (15.999) + 2 × H (1.008) = 74.093 g/mol.
What is Avogadro's number?
Avogadro's number (NA) = 6.02214076 × 1023 mol−1. It is the number of entities in one mole. This exact value was defined in 2019 as part of the SI redefinition.