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Molar mass of methane

The molar mass of methane (CH₄) is 16.043 g/mol: the sum of the atomic weights 12.011 + 4 × 1.0080. School problems round it to 16 g/mol (C = 12, H = 1).

CH4 methane

Molar mass

16.043 g/mol

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

Breakdown by element

M(CH4) = 12.011 + 4 × 1.0080 = 16.043 g/mol

The result is rounded to the precision of the least precise atomic weight. Atomic weights from IUPAC (CIAAW). Agrees with PubChem: 16.043 g/mol. PubChem CID 297

What is methane?

Methane is the simplest hydrocarbon and the main component of natural gas. It is a colourless, odourless gas, lighter than air; a smell is added to household gas on purpose so that leaks can be noticed.

Methane burns with a blue flame: CH₄ + 2O₂ → CO₂ + 2H₂O. It forms when plant and animal matter rots without air, in swamps for example, and it is a greenhouse gas.

Properties

State at 25 °C
Gas
Density
0.717 g/L 0 °C
Melting point
−182.5 °C
Boiling point
−161.5 °C
Solubility in water
practically insoluble 22 mg/L, 25 °C

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

Molar mass problems with methane

For school problems (C = 12, H = 1): M(CH₄) = 16 g/mol

  1. Problem 1

    How many moles are in 8 g of CH₄?

    n = m ÷ M = 8 g ÷ 16 g/mol

    Answer: 0.5 mol

  2. Problem 2

    What is the mass of 0.25 mol of CH₄?

    m = n × M = 0.25 mol × 16 g/mol

    Answer: 4 g

  3. Problem 3

    What is the mass percentage of C in CH₄?

    w(C) = M(C) ÷ M(CH₄) = 12 ÷ 16 = 0.75

    Answer: 75.0%

  4. Problem 4

    How many molecules are in 4 mol of CH₄?

    N = n × NA = 4 mol × 6.02 × 10²³ mol⁻¹

    Answer: 2.408 × 10²⁴

  5. Problem 5

    What volume does 48 g of CH₄ take up at STP?

    n = m ÷ M = 48 g ÷ 16 g/mol = 3 mol

    V = n × Vm = 3 mol × 22.4 L/mol

    STP here: 0 °C and 1 atm (101.3 kPa).

    Answer: 67.2 L

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.