Science calculator

Moles, grams and concentration.

Convert moles to grams, grams to moles, or work out the molar concentration you get from dissolving a weighed mass in a known volume. Grams and moles are not interchangeable units — every conversion between them needs the substance's molar mass, which is why this is a calculation rather than a unit conversion.

Relationship

Amount n

Sample mass m

Molar mass M

Amount nSolved

—

chemistry amount of substance

Number of entities nNₐ: —

Display precision

n = \frac{m}{M}

c = \frac{n}{V}

c = \frac{m}{M V}

n amount of substance · m sample mass · M molar mass · c amount concentration · V solution volume

Assumptions

Amount concentration uses the volume of the finished solution, not the volume of solvent you started with. Dissolving a solid changes the volume, which is why a volumetric flask is made up to the mark after the solid has gone in.
The sample mass belongs to the stated pure substance or formula units represented by the molar mass.
Molar mass uses the same chemical formula and isotopic convention as the sample.
Concentration means amount concentration in mol per volume of final solution, not mass concentration.
The entity count uses the exact Avogadro constant, 6.02214076 × 10²³ mol⁻¹.

How it works

One mole contains a fixed number of specified entities. Molar mass tells you the mass of one mole of those atoms, molecules, ions or formula units.

Amount concentration divides moles of solute by the total solution volume. A concentration of 1 mol/L is 1000 mol/m³ in SI units.

To convert moles to grams, multiply the amount by the molar mass. To convert grams to moles, divide the mass by it. Leave the value you want blank and the calculator does whichever rearrangement that implies.

Making up a solution combines both steps: c = m/(MV). Weigh the solid, note its molar mass, make up to a known volume, and leave the concentration blank. Leave the mass blank instead and it tells you what to weigh out for a target concentration.

Choose a relationship and leave one field blank. State the chemical entity alongside a numerical answer in assessed work.

Common questions this answers: how to convert moles to grams (multiply by the molar mass), how to convert grams to moles (divide by it), what 1 mole of water weighs (18.02 g, since M = 18.02 g/mol), and what concentration 5.844 g of sodium chloride makes up to 100 mL (1 mol/L).

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