The density of water at room temperature is 1.0 g/mL. How many molecules are there in a drop of water if its volume is 0.05 mL?

To find the number of molecules in a drop of water, we need to use the given density and volume of water.

Step 1: Convert the volume of water from milliliters (mL) to liters (L). Given: Volume of water = 0.05 mL To convert mL to L, divide by 1000: 0.05 mL ÷ 1000 = 0.00005 L

Step 2: Use the density of water to find the mass of the water. Given: Density of water = 1.0 g/mL Mass = Density × Volume Mass = 1.0 g/mL × 0.05 mL Mass = 0.05 g

Step 3: Convert the mass of water from grams (g) to moles (mol). To convert grams to moles, we need to know the molar mass of water. The molar mass of water (H2O) is approximately 18.015 g/mol. Moles = Mass ÷ Molar mass Moles = 0.05 g ÷ 18.015 g/mol Moles ≈ 0.00277 mol

Step 4: Use Avogadro's number to find the number of molecules. Avogadro's number is approximately 6.022 × 10^23 molecules/mol. Number of molecules = Moles × Avogadro's number Number of molecules ≈ 0.00277 mol × 6.022 × 10^23 molecules/mol Number of molecules ≈ 1.67 × 10^21 molecules

Therefore, there are approximately 1.67 × 10^21 molecules in a drop of water with a volume of 0.05 mL.