Question

Which best compares 1 mol of sodium chloride to 1 mol of aluminum chloride?
Both have the same molar mass.
Both have the same number of ions.
Both are made up of 6.02 mc014-1.jpg 1023 molecules.
Both are made up of 6.02 mc014-2.jpg 1023 formula units.

Answer 1

Both are made up of 6.02 × 10^23 formula units.

Reason: one mole of any substance contains Avogadro's number of its basic units. For ionic compounds those are formula units (not molecules). NaCl and AlCl3 therefore each contain 6.02×10^23 formula units, but they differ in molar mass and in number of ions per formula unit (NaCl → 2 ions; AlCl3 → 4 ions).