Volume of a Drop of Water and the Number of Molecules it Contains
When we think about a drop of water, we often consider it a small amount, but have you ever wondered how many molecules are present in a single drop of water? To understand this, let's first explore the volume of a drop of water.
Volume of a Drop of Water
One milliliter (mL) of water is equivalent to 1,000 microliters (µL). A drop of water is approximately 0.05 mL or 50 µL in volume. This means that 1 mL of water contains approximately 20 drops.
Calculating the Number of Molecules in a Drop of Water
To calculate the number of molecules in a drop of water, we need to know the molecular weight of water (H2O) and Avogadro's number.
Molecular Weight of Water (H2O)
The molecular weight of water is 18.0153 g/mol. This value is the sum of the atomic weights of two hydrogen atoms (1.00794 u each) and one oxygen atom (15.9994 u).
Avogadro's Number
Avogadro's number is a fundamental constant in chemistry, defined as 6.022140857 × 10^23 particles (atoms or molecules). This number represents the number of particles in one mole of a substance.
Calculating the Number of Molecules in a Drop of Water
Now, let's calculate the number of molecules in a drop of water. Assuming a drop of water has a volume of approximately 50 µL (0.05 mL), we can calculate the number of moles of water as follows:
Number of moles of water = Mass of water (in grams) / Molecular weight of water = (Density of water * Volume of a drop of water) / Molecular weight of water = (1 g/mL * 0.05 mL) / 18.0153 g/mol ≈ 2.78 × 10^-5 mol
Now, we can calculate the number of molecules in a drop of water using Avogadro's number:
Number of molecules = Number of moles × Avogadro's number = 2.78 × 10^-5 mol × 6.022140857 × 10^23 molecules/mol ≈ 1.67 × 10^19 molecules
Therefore, a drop of water contains approximately 1.67 × 10^19 molecules. This is an enormous number, emphasizing the incredible complexity and beauty of the molecular structure of water.
