To determine the number of atoms present in a given mass of a substance, you need to use Avogadro's number and the molar mass of the substance.
The molar mass of aluminum (Al) is approximately 26.98 grams per mole (g/mol). Avogadro's number is approximately 6.022 x 10^23 atoms per mole.
To find the number of moles of aluminum in 9.0 grams, you divide the given mass by the molar mass:
Number of moles = Mass / Molar mass = 9.0 g / 26.98 g/mol ≈ 0.334 moles
Next, to find the number of atoms, multiply the number of moles by Avogadro's number:
Number of atoms = Number of moles * Avogadro's number ≈ 0.334 mol * (6.022 x 10^23 atoms/mol) ≈ 2.011 x 10^23 atoms
Therefore, there are approximately 2.011 x 10^23 atoms in 9.0 grams of aluminum.