1. Find the molar mass of H₂O:
* H: 1.01 g/mol (x 2 = 2.02 g/mol)
* O: 16.00 g/mol
* Total: 18.02 g/mol
2. Convert grams to moles:
* Moles = (grams) / (molar mass)
* Moles = 3.5 g / 18.02 g/mol
* Moles ≈ 0.194 mol
3. Use Avogadro's number to find the number of molecules:
* Avogadro's number: 6.022 x 10²³ molecules/mol
* Number of molecules = (moles) x (Avogadro's number)
* Number of molecules ≈ 0.194 mol x 6.022 x 10²³ molecules/mol
* Number of molecules ≈ 1.17 x 10²³ molecules
Therefore, there are approximately 1.17 x 10²³ water molecules in 3.5 grams of H₂O.
