How do you calculate molecular is 45g of water?

To calculate the number of molecules in 45 grams of water (H₂O), first determine the molar mass of water, which is approximately 18 g/mol. Then, divide the mass of water by its molar mass: 45 g ÷ 18 g/mol = 2.5 moles of water. Finally, use Avogadro's number (approximately (6.022 \times 10^{23}) molecules/mol) to find the number of molecules: 2.5 moles × (6.022 \times 10^{23}) molecules/mol ≈ (1.51 \times 10^{24}) molecules.