The density of water is 1.00 g/ml at 4°c. how many water molecules are present in 2.56 ml of water at this temperature?

             8.55 × 10²² Molecules

Solution:

Step 1: Calculate the Mass of Water as;

                       Density  =  Mass ÷ Volume

Solving for Mass,

                       Mass  =  Density × Volume

Putting values,

                       Mass  =  1 g.mL⁻¹ × 2.56 mL

                       Mass  =  2.56 g

Step 2: Calculate Moles of Water as,

                       Moles  =  Mass ÷ M.Mass

Putting values,

                       Moles  =  2.56 g ÷ 18 g.mol⁻¹

                       Moles  =  0.142 mol

Step 3: Calculate Number of Molecules of Water as,

                       # of Molecules  =  Moles × 6.022 × 10²³

Putting value of mole,

                       # of Molecules  =  0.142 × 6.022 × 10²³

                       # of Molecules  =  8.55 × 10²² Molecules