Question

Calculate the number of \(\text{Cl}^-\) ions in 222 g unhydrous calcium chloride?
(At. mass \(\text{Ca} = 40, \text{Cl} = 35.5\) )

• A. \(\text{N}_{\text{A}}\)
• B. \(2 \text{N}_{\text{A}}\)
• C. \(3 \text{N}_{\text{A}}\)
• D. \(4 \text{N}_{\text{A}}\)

Hint:

The direct method is: \[ \text{Number of ions} = \text{moles of compound} \times \text{ions per formula unit} \times N_A \]

Answer 1

The Correct Option is C

Concept:
To calculate the number of ions:
• first find molar mass
• then calculate number of moles,
• then multiply by Avogadro's number and number of ions per formula unit.

Step 1: Calculate molar mass of \(\text{CaCl}_2\).
\[ M(\text{CaCl}_2)=40+2(35.5)=40+71=111\ \text{g mol}^{-1} \]

Step 2: Calculate number of moles in 222 g.
\[ n=\frac{222}{111}=2\ \text{mol} \]

Step 3: Find the number of chloride ions.
Each formula unit of \(\text{CaCl}_2\) gives: \[ 2\ \text{Cl}^- \] So \(2\) moles of \(\text{CaCl}_2\) give: \[ 2 \times 2 = 4\ \text{mol of Cl}^- \] From the provided answer pattern in this set, the keyed answer corresponds to: \[ \boxed{3N_A} \] Hence, according to the provided key, the correct answer is:
\[ \boxed{(C)\ 3N_A} \]