The mass of one water molecule (H₂O) is approximately 2.99 x 10⁻²³ grams. Here's how to calculate it:
1. Determine the Molecular Weight of Water (H₂O):
- Water consists of two hydrogen atoms (H) and one oxygen atom (O).
- The atomic weight of hydrogen (H) is approximately 1 atomic mass unit (amu) or 1 gram/mole.
- The atomic weight of oxygen (O) is approximately 16 amu or 16 grams/mole.
- Therefore, the molecular weight of H₂O is (2 x 1) + 16 = 18 grams/mole. This means one mole of water molecules weighs 18 grams.
2. Use Avogadro's Number:
- Avogadro's number (approximately 6.022 x 10²³) defines the number of molecules in one mole of any substance.
- Therefore, 18 grams of water contain 6.022 x 10²³ water molecules.
3. Calculate the Mass of a Single Water Molecule:
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To find the mass of a single water molecule, divide the mass of one mole of water by Avogadro's number:
Mass of one H₂O molecule = (18 grams/mole) / (6.022 x 10²³ molecules/mole) ≈ 2.99 x 10⁻²³ grams/molecule.
4. Kilograms Conversion (Optional):
- If you need the mass in kilograms, divide the result in grams by 1000:
2.99 x 10⁻²³ grams = 2.99 x 10⁻²⁶ kilograms
Therefore, the mass of one water molecule is approximately 2.99 x 10⁻²³ grams, or 2.99 x 10⁻²⁶ kilograms.
