1. The problem is to convert the given weight/volume percentage expression into an equation. 2. The formula for weight/volume percentage (% w/v) is: $$\%\ \mathrm{w/v} = \frac{\text{mass of solute (g)}}{\text{volume of solution (mL)}} \times 100\ \mathrm{mL}$$ 3. Given: mass of Fe = 0.1123 g, volume of solution = 25.0 mL. 4. Substitute the values into the formula: $$\%\ \mathrm{w/v} = \frac{0.1123\ \mathrm{g}}{25.0\ \mathrm{mL}} \times 100\ \mathrm{mL}$$ 5. Calculate the division: $$\frac{0.1123}{25.0} = 0.004492$$ 6. Multiply by 100 mL: $$0.004492 \times 100 = 0.4492\%$$ 7. Rounded to three significant figures, the % w/v is 0.449%.