Final answer:
To calculate the number of atoms in a sample of gallium, divide the mass by the molar mass and then multiply by Avogadro's number.
Step-by-step explanation:
To calculate the number of atoms in a sample of gallium, we need to use Avogadro's number which is 6.022 × 10²³ atoms/mol. First, we need to convert the mass of gallium to moles by dividing it by the molar mass of gallium which is 69.723 g/mol.
So, (2.85 × 10³ g) / (69.723 g/mol) = 40.9105 mol.
Finally, we multiply the moles by Avogadro's number: 40.9105 mol × 6.022 × 10²³ atoms/mol = 2.460 × 10²⁵ atoms. Therefore, there are approximately 2.460 × 10²⁵ atoms in 2.85x10³ g of gallium.