Molar mass of lactic acid (C₃H₆O₃)

The molar mass of lactic acid (C₃H₆O₃) is 90.078 g/mol, summed from the IUPAC standard atomic weights of C x 3, H x 6, O x 3.

Mass of sample

Amount of substance

mol

Molar mass

90.078g/mol

= Exact Molar mass of lactic acid

Moles in the sample mass: 0.111 014 9 mol
Mass of that amount of substance: 90.078
Molecules in the sample mass: 6.68547e+22

Show the working

Mass of sample = 10
Amount of substance = 1
Molar mass = 12.011*3 + 1.008*6 + 15.999*3 = 90.078
Moles in the sample mass = 10 / 90.078 = 0.111 015
Mass of that amount of substance = 1 * 90.078 = 90.078
Molecules in the sample mass = 0.111 015 * NA = 6.68547e+22

Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.

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The formula

Molar mass = sum over elements of (atomic weight x number of atoms)
For C₃H₆O₃: 12.011 x 3 + 1.008 x 6 + 15.999 x 3 = 90.078 g/mol
Moles = mass / molar mass; mass = moles x molar mass
Molecules = moles x 6.02214076 x 10^23 (the Avogadro constant, exact by definition)

Molar mass in grams per mole is numerically equal to the molecular mass in daltons, so this figure doubles as the molecular weight.

Atomic weights are the IUPAC 2021 standard values. Several elements have a range rather than a single value because isotope ratios vary between sources; the conventional single value is used here.

Composition by mass

Element	Atoms	Atomic weight	Contribution (g/mol)	Share of mass
Oxygen (O)	3	15.999	47.997	53.284 %
Carbon (C)	3	12.011	36.033	40.002 %
Hydrogen (H)	6	1.008	6.048	6.7142 %

Contributions add to the molar mass of 90.078 g/mol. Atomic weights are the IUPAC 2021 standard values.

Frequently asked

What is the molar mass of lactic acid?

90.078 g/mol, for the formula C₃H₆O₃.

How do you convert grams of lactic acid to moles?

Divide the mass in grams by 90.078 g/mol. One gram of lactic acid is 0.0111015 mol.

How many grams are in one mole of lactic acid?

90.078 g, by definition of the molar mass.

Is molar mass the same as molecular weight?

Numerically yes, for the purposes of this calculation. Molecular weight is a dimensionless ratio and molar mass carries units of g/mol, but the digits are identical.

Where the numbers come from

IUPAC 2021 standard atomic weights; Avogadro constant fixed by the 2019 SI.