Final answer:
To find the mass of 1.8 x 10²³ molecules of H₂O, convert the number of molecules to moles using Avogadro's number and then multiply by the molar mass of H₂O (18.015 g/mol) to get the mass in grams, which is approximately 5.386 grams.
Step-by-step explanation:
To calculate the mass in grams of 1.8 x 10²³ molecules of H₂O (water), we first need to determine how many moles this number of molecules represents. We'll use Avogadro's number (6.022 x 10²³ mol¹), which is the number of molecules in one mole of any substance.
First, divide the given number of molecules by Avogadro's number to find the number of moles:
Number of moles = 1.8 x 10²³ molecules / 6.022 x 10²³ molecules/mol = 0.299 moles
Next, using the molar mass of water, which is 18.015 g/mol, we can calculate the mass:
Mass of H₂O (in grams) = 0.299 moles x 18.015 g/mol = 5.386 g
Thus, 1.8 x 10²³ molecules of H₂O have a mass of approximately 5.386 grams.