To calculate the mass of 1.5E23 water molecules, we need to determine the number of moles and then multiply it by the molar mass of water.

Convert 1.5E23 to a decimal number: 1.5 x 10^23

The number of moles (n) can be calculated by dividing the number of molecules by Avogadro's number (Nₐ), which is approximately 6.022 x 10^23 molecules per mole.

n = (1.5 x 10^23 molecules) / (6.022 x 10^23 molecules/mole)

n ≈ 0.248 moles

Now, we can determine the mass (m) using the molar mass of water (M), which is approximately 18.015 grams per mole.

m = n × M

m ≈ 0.248 moles × 18.015 g/mole

m ≈ 4.47 grams

Therefore, the mass of 1.5E23 water molecules is approximately 4.47 grams.