The mass of a single molecule of water (H2O) can be calculated using its molecular weight. The molecular weight of water consists of the weights of two hydrogen atoms and one oxygen atom.
1. The atomic weight of hydrogen (H) is approximately 1 gram/mole. Since there are two hydrogen atoms in a water molecule, this contributes about 2 grams/mole (2 x 1).
2. The atomic weight of oxygen (O) is about 16 grams/mole. Therefore, for one water molecule, the total molecular weight is:
2 (from hydrogen) + 16 (from oxygen) = 18 grams/mole.
Since Avogadro’s number tells us that one mole contains approximately 6.022 x 1023 molecules, we can find the mass of a single molecule of water by dividing the molecular weight by Avogadro’s number:
Mass of one molecule of water = Weight of 1 mole of H2O / Avogadro’s number = 18 grams/mole / 6.022 x 1023 molecules/mole.
Calculating this gives:
Mass of one molecule of water ≈ 2.99 x 10-23 grams.
Thus, the mass of a single molecule of water is approximately 2.99 x 10-23 grams.