What is the molarity of Fe2+ ions in an aqueous solution with a volume of 450.mL that contains 200. g of iron (II) chloride, FeCl2?
The Correct Answer and Explanation is:
To calculate the molarity (M) of Fe²⁺ ions in the solution, follow these steps:
Step 1: Write the chemical formula and dissociation
Iron(II) chloride (FeCl₂) dissolves in water as follows: FeCl2(s)→Fe2+(aq)+2Cl−(aq)\text{FeCl}_2 (s) \rightarrow \text{Fe}^{2+} (aq) + 2\text{Cl}^{-} (aq)FeCl2(s)→Fe2+(aq)+2Cl−(aq)
From this equation, 1 mole of FeCl₂ produces 1 mole of Fe²⁺ ions.
Step 2: Calculate molar mass of FeCl₂
- Fe: 55.85 g/mol
- Cl: 35.45 g/mol × 2 = 70.90 g/mol
- Molar mass of FeCl₂ = 55.85 + 70.90 = 126.75 g/mol
Step 3: Convert mass to moles
You are given 200. g of FeCl₂, so: Moles of FeCl2=200. g126.75 g/mol≈1.578 mol\text{Moles of FeCl}_2 = \frac{200. \text{ g}}{126.75 \text{ g/mol}} \approx 1.578 \text{ mol}Moles of FeCl2=126.75 g/mol200. g≈1.578 mol
Since 1 mole of FeCl₂ yields 1 mole of Fe²⁺: Moles of Fe2+=1.578 mol\text{Moles of Fe}^{2+} = 1.578 \text{ mol}Moles of Fe2+=1.578 mol
Step 4: Convert volume from mL to L
450. mL=0.450 L450. \text{ mL} = 0.450 \text{ L}450. mL=0.450 L
Step 5: Calculate molarity
Molarity (M)=moles of soluteliters of solution=1.5780.450≈3.51 M\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}} = \frac{1.578}{0.450} \approx \boxed{3.51 \, \text{M}}Molarity (M)=liters of solutionmoles of solute=0.4501.578≈3.51M
✅ Final Answer:
The molarity of Fe²⁺ ions in the solution is 3.51 M.
