What is the total number of ions in 0.250 mol of magnesium chloride, MgCl2? (Avogadro constant = 6.02 × 10^23 mol^-1)
Show the answer and explanation
Correct answer
A. 4.52 × 10^23
Principle or equation
Each formula unit of MgCl2 dissociates into 3 ions (1 Mg²⁺ and 2 Cl⁻). Total ions = moles × Avogadro constant × number of ions per formula unit.
Why this answer is correct
Number of ions per formula unit = 1 + 2 = 3. Total ions = 0.250 mol × 6.02 × 10^23 mol⁻¹ × 3 = 0.250 × 6.02 × 3 × 10^23 = 4.515 × 10^23, which rounds to 4.52 × 10^23.
Example
For 0.100 mol of CaCl2 (3 ions per formula unit): total ions = 0.100 × 6.02 × 10^23 × 3 = 1.806 × 10^23.
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