You find water molecules by first determining the mass of the water sample, then converting that mass to moles, and finally converting moles to the number of molecules.
Here's a step-by-step guide, incorporating information from the provided reference:
Steps to Find Water Molecules
- Determine the Mass (in grams): You need to know the weight of the water sample you're working with. This is usually measured in grams.
- Convert Grams to Moles:
- The reference mentions that you divide the grams of water by the molar mass of water to convert grams to moles.
- The molar mass of water (H₂O) is approximately 18.015 g/mol.
- Formula: Moles of water = (Mass of water in grams) / (18.015 g/mol)
- Convert Moles to Molecules:
- The reference states that once you have the number of moles, you multiply by Avogadro's number to get the number of molecules.
- Avogadro's number is approximately 6.022 x 10²³.
- Formula: Number of molecules = (Moles of water) x (6.022 x 10²³ molecules/mol)
Example
Let's say you have 36 grams of water:
| Step | Calculation | Result |
|---|---|---|
| 1. Find the mass | 36 grams (Given) | 36 grams |
| 2. Convert to Moles | 36 grams / 18.015 g/mol | Approximately 2 moles |
| 3. Convert to Molecules | 2 moles * 6.022 x 10²³ molecules/mol | Approximately 1.2044 x 10²⁴ molecules |
Key Concepts
- Molar Mass: The mass of one mole of a substance (in grams per mole).
- Moles: A unit of measurement for the amount of a substance.
- Avogadro's Number: The number of particles (atoms, molecules, etc.) in one mole of a substance, approximately 6.022 x 10²³.
In summary, by following these steps, you can calculate the number of water molecules present in a given sample of water, which is described in the reference as using molar mass and Avogadro's number.
