Answer:
Step-by-step explanation:
To express 71.7 g of H2O in molecules to three significant figures, we need to use the concept of molar mass and Avogadro's number.
1) Molar mass of H2O: The molar mass of H2O can be calculated by adding up the atomic masses of its constituent atoms. Hydrogen (H) has an atomic mass of approximately 1 g/mol, and oxygen (O) has an atomic mass of approximately 16 g/mol. Therefore, the molar mass of H2O is 1 g/mol (2 hydrogen atoms) + 16 g/mol (1 oxygen atom) = 18 g/mol.
2) Moles of H2O: To find the number of moles in 71.7 g of H2O, we divide the given mass by the molar mass of H2O:
71.7 g H2O / 18 g/mol = 3.98 mol (rounded to three significant figures).
3) Avogadro's number: Avogadro's number is a constant that represents the number of particles (atoms, molecules, ions) in one mole of a substance. It is approximately 6.022 x 10^23 particles/mol.
4) Number of molecules: To convert moles of H2O to molecules, we multiply the number of moles by Avogadro's number:
3.98 mol x 6.022 x 10^23 molecules/mol = 2.40 x 10^24 molecules of H2O (rounded to three significant figures).
Therefore, 71.7 g of H2O is equivalent to approximately 2.40 x 10^24 molecules of H2O.