Molar mass, also known as molecular weight, is the mass of one mole of a substance. It is calculated by adding the atomic masses of all the atoms in a molecule or formula unit. You can find the atomic masses of elements on the periodic table.
Here's how to calculate molar mass:
- Identify the chemical formula of the substance. This tells you the types of atoms and their quantities present in the molecule or formula unit.
- Look up the atomic mass of each element on the periodic table. The atomic mass is usually found below the element's symbol and is expressed in atomic mass units (amu).
- Multiply the atomic mass of each element by the number of atoms of that element in the formula.
- Add the results from step 3 to get the molar mass.
Example:
Let's calculate the molar mass of water (H2O).
- Step 1: The chemical formula for water is H2O, meaning it contains two hydrogen atoms and one oxygen atom.
- Step 2: The atomic mass of hydrogen (H) is 1.008 amu, and the atomic mass of oxygen (O) is 15.9994 amu.
- Step 3: (1.008 amu/H atom x 2 H atoms) + (15.9994 amu/O atom x 1 O atom) = 2.016 amu + 15.9994 amu
- Step 4: The molar mass of water is 18.0154 amu.
Note: Molar mass is usually expressed in grams per mole (g/mol). This is because one mole of any substance contains Avogadro's number of particles (6.022 x 1023).
Practical Insights:
- Molar mass is a fundamental concept in chemistry and is used in many calculations, such as determining the amount of reactant needed for a specific reaction or calculating the concentration of a solution.
- You can use online calculators or software to quickly calculate molar mass.
