Mass divided by molar mass gives the number of moles of a substance.
Understanding Moles and Molar Mass
To fully grasp this concept, let's define key terms:
- Mole: A mole is a unit of measurement used in chemistry to express amounts of a chemical substance. It is defined as exactly 6.02214076 × 1023 elementary entities (like atoms, molecules, ions) of a given substance.
- Molar Mass: The molar mass of a substance is the mass of one mole of that substance. It's usually expressed in grams per mole (g/mol). Each substance has a unique molar mass. According to the reference, the molar mass of a substance is fixed for a given substance.
Calculation: Mass Divided by Molar Mass
The calculation is straightforward:
This ratio is used frequently in chemistry for converting between mass and the number of moles.
Example:
Let's say you have 36 grams of water (H2O). The molar mass of water is approximately 18 g/mol.
- Number of moles of H2O = 36 g / 18 g/mol
- Number of moles of H2O = 2 mol
This means that 36 grams of water contain 2 moles of water molecules.
Why is This Important?
Knowing the number of moles is crucial in chemistry because:
- It allows us to relate the mass of substances to the number of particles (atoms, molecules, etc.).
- It's essential in stoichiometry for calculating reactant and product amounts in chemical reactions.
- It's key for understanding the composition of mixtures and solutions.
- According to the provided reference, "the ratio of the given mass of the substance to its molar mass gives the total number of moles of the substance."
Summary
| Term | Definition |
|---|---|
| Mass | Amount of a substance usually in grams (g) |
| Molar Mass | Mass of one mole of a substance, usually in grams per mole (g/mol) |
| Number of Moles | Amount of a substance measured in moles (mol) |
In conclusion, dividing the mass of a substance by its molar mass directly yields the number of moles of that substance.
