Question

How many atoms are in a sample of 72.8 grams calcium (Ca)? 1.76 × 1027 atoms 1.09 × 1024 atoms 4.85 × 10-21 atoms 3.02 × 10-24 atoms

Answer 1

You can find the number of atoms in calcium by multiplying a given mole of Calcium by Avogadro's number since each mole of a substance contains 6.03 × 10²³.

Now, mol of Ca = mass of Ca ÷ molar mass of Ca
mol of Ca = 72.8 g ÷ 40 g/mol
mol of Ca = 1.82 mol

⇒ atoms of Ca = 1.82 mol × (6.02 × 10²³ atoms/mole)
= 1.096 × 10²⁴ atoms [OPTION 2]