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Molar mass

One mole is 6.02·10²³ particles. The molar mass is the mass of one mole, in grams per mole, and numerically it equals the sum of the atomic masses in the formula. The atomic masses used here are H 1.008, C 12.01 and O 16.00. Add them with the right count of each atom. For water that is two hydrogens and one oxygen. For carbon dioxide it is one carbon and two oxygens. Rounding to two decimals is what the problems use.

M = \sum n_i M_i

molar mass from atomic masses

Symbols

$M$	molar mass	g/mol
$n_i$	count of that atom in the formula

Example

Water: $2 \cdot 1.008 + 16.00 \approx 18.02$ g/mol.

Carbon dioxide: $12.01 + 2 \cdot 16.00 = 44.01$ g/mol.

Count the atoms in the formula before you multiply. In Ca(OH)2 there are two oxygens and two hydrogens.

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Part of Chemistry 1: Amount of substance and concentration.