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Molar mass of ethanol

The molar mass of ethanol (C₂H₅OH) is 46.069 g/mol: the sum of the atomic weights 2 × 12.011 + 6 × 1.0080 + 15.999. School problems round it to 46 g/mol (C = 12, H = 1, O = 16).

C2H5OH ethanol

Also called ethyl alcohol

Molar mass

46.069 g/mol

For school problems (C = 12, H = 1, O = 16): 46 g/mol

Breakdown by element

M(C2H5OH) = 2 × 12.011 + 6 × 1.0080 + 15.999 = 46.069 g/mol

The result is rounded to the precision of the least precise atomic weight. Atomic weights from IUPAC (CIAAW). Agrees with PubChem: 46.07 g/mol. PubChem CID 702

What is ethanol?

Ethanol (ethyl alcohol) is a colourless, volatile liquid with a typical smell that mixes with water in any proportion. It is made by yeast fermenting sugars, and industrially also from ethene.

Ethanol is a solvent, a fuel and an antiseptic; it is the alcohol in alcoholic drinks and is poisonous in large amounts. It burns with a pale blue, almost invisible flame: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.

Properties

State at 25 °C
Liquid
Density
0.789 g/cm³ 20 °C
Melting point
−114.14 °C
Boiling point
78.2 °C
Solubility in water
mixes with water in any proportion

Sources: PubChem (HSDB, NIOSH), Wikipedia (CRC Handbook), NIST Chemistry WebBook; each value agrees in two of them.

Molar mass problems with ethanol

For school problems (C = 12, H = 1, O = 16): M(C₂H₅OH) = 46 g/mol

  1. Problem 1

    How many moles are in 92 g of C₂H₅OH?

    n = m ÷ M = 92 g ÷ 46 g/mol

    Answer: 2 mol

  2. Problem 2

    What is the mass of 0.2 mol of C₂H₅OH?

    m = n × M = 0.2 mol × 46 g/mol

    Answer: 9.2 g

  3. Problem 3

    What is the mass percentage of C in C₂H₅OH?

    w(C) = 2 × M(C) ÷ M(C₂H₅OH) = 2 × 12 ÷ 46 ≈ 0.522

    Answer: 52.2%

  4. Problem 4

    How many molecules are in 1.5 mol of C₂H₅OH?

    N = n × NA = 1.5 mol × 6.02 × 10²³ mol⁻¹

    Answer: 9.03 × 10²³

What is molar mass?

Molar mass M is the mass of one mole of a substance, about 6.022 × 10²³ of its particles. It is measured in grams per mole (g/mol).

To find it, add up the atomic weights of all the atoms in the formula: multiply each element’s atomic weight by its subscript, the number of its atoms. In g/mol, the molar mass equals the relative molecular mass Mr.

For water: M(H₂O) = 2 × 1.0080 + 15.999 = 18.015 g/mol.