Molar mass is fundamentally derived from atomic mass; it's the sum of the atomic masses of all atoms within a molecule or compound.
Understanding the Connection
The key difference lies in what each term represents:
- Atomic Mass: Refers to the mass of a single atom of an element. It's typically expressed in atomic mass units (amu), although in practice, we often use grams per mole (g/mol) which is numerically equivalent.
- Molar Mass: Is the mass of one mole of a substance (element or compound) and is always measured in grams per mole (g/mol).
The link is that to calculate the molar mass of a compound, you sum the atomic masses of each individual atom within that compound's molecular formula.
Calculating Molar Mass
Here's how to determine molar mass from atomic masses:
- Identify the Molecular Formula: Know the chemical formula of the compound you are working with.
- Find Atomic Masses: Look up the atomic mass of each element in the compound from the periodic table.
- Multiply by Subscripts: Multiply each element’s atomic mass by its corresponding subscript in the molecular formula.
- Sum the Masses: Add up the values of all the elements to determine the molar mass of the compound.
Example: Let's calculate the molar mass of water (H₂O).
- Atomic mass of Hydrogen (H) ≈ 1 g/mol
- Atomic mass of Oxygen (O) ≈ 16 g/mol
Since there are two hydrogen atoms and one oxygen atom, the calculation is:
(2 1 g/mol) + (1 16 g/mol) = 18 g/mol. Therefore the molar mass of water is approximately 18 g/mol.
Key Takeaways
- Atomic mass is for individual atoms, while molar mass applies to one mole of a substance (either element or compound).
- The molar mass of a compound is the sum of the atomic masses of its constituent elements, considering the quantity of each element in its molecular formula.
- The reference confirms that atomic mass is for a single element while molar mass is for a compound which is calculated by summing atomic masses of all constituent elements in the compounds molecular formula. It also notes that both atomic mass and molar mass have units of g/mol.
Practical Implications
Understanding molar mass allows for accurate conversions between mass and moles in chemical reactions, and for performing stoichiometric calculations.
