The difference between a mole and gram molecular mass lies in what they represent: a mole is a number of molecules, while gram molecular mass is the mass of that specific number of molecules (one mole) expressed in grams.
Here's a breakdown:
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Mole: A mole (symbol: mol) is a unit of measurement for the amount of a substance in chemistry. It represents a specific number of particles (atoms, molecules, ions, etc.). This number is Avogadro's number, which is approximately 6.022 x 1023. Think of it like "a dozen," which always means 12 of something, regardless of what that something is. A mole always represents 6.022 x 1023 entities.
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Gram Molecular Mass: Gram molecular mass (also known as molar mass) is the mass of one mole of a particular molecular substance expressed in grams. It's numerically equal to the molecular weight of the substance but has units of grams per mole (g/mol). The gram molecular mass is obtained by adding up the atomic masses of all the atoms in the molecule, as found on the periodic table, and expressing the result in grams.
To illustrate:
- Consider water (H2O).
- The molecular weight of water is approximately 18.015 atomic mass units (amu). This is calculated by adding (2 x atomic mass of Hydrogen) + (1 x atomic mass of Oxygen) = (2 x 1.008 amu) + (1 x 16.00 amu) ≈ 18.015 amu.
- Therefore, the gram molecular mass (or molar mass) of water is 18.015 grams per mole (g/mol).
- One mole of water contains 6.022 x 1023 water molecules and has a mass of 18.015 grams.
In summary:
| Feature | Mole | Gram Molecular Mass (Molar Mass) |
|---|---|---|
| Definition | A unit for amount of substance | The mass of one mole of a substance in grams. |
| Represents | A specific number of entities (Avogadro's Number) | A specific mass corresponding to one mole of the substance. |
| Units | mol | g/mol |
| Value | 6.022 x 1023 entities | Varies depending on the substance. |
