Av Michael Judge | Uppdaterad 30 augusti 2022
In chemistry, a mole is the unit that links the mass of a substance to the number of molecules or atoms it contains. One mole equals 6.022 × 10²³ entities—Avogadro’s number—making it an essential tool for quantitative analysis.
Start with the exact molecular formula of the compound. The formula tells you how many atoms of each element are present in one molecule. For example, water is H₂O, meaning each molecule contains two hydrogen atoms and one oxygen atom.
Consult a periodic table to find the atomic weight (also called atomic mass) of each element in the formula. Typical values are 1.008 g/mol for hydrogen and 16.00 g/mol for oxygen.
Multiply each element’s atomic weight by the number of atoms of that element, then sum the results:
(2 × 1.008) + (1 × 16.00) = 18.016 g/mol
This total, expressed in grams per mole, is the molar mass of the compound.
Divide the sample’s mass (in grams) by the molar mass to obtain the number of moles:
25 g H₂O ÷ 18.016 g/mol ≈ 1.39 mol
Follow these steps to calculate moles for any chemical, whether you’re working in a lab or studying chemistry coursework.
Att bemästra mullvadsberäkningar låser upp möjligheten att utföra exakta stökiometriska beräkningar, designexperiment och tolka analytisk data.
