A student dilutes 25.0 mL of an HCl solution to a final volume of 250.0 mL. The concentration of the diluted solution is found to be 0.15 M. What was the original concentration of the HCl solution before dilution?

• A. 1.50 M
• B. 0.25 M
• C. 2.50 M
• D. 0.040 M

Answer: (A)

Verified step by step guidance

1. Identify the known values: initial volume \( V_1 = 25.0 \text{ mL} \), final volume \( V_2 = 250.0 \text{ mL} \), and final concentration \( C_2 = 0.15 \text{ M} \). The initial concentration \( C_1 \) is what we need to find.
2. Recall the dilution equation which relates the concentrations and volumes before and after dilution: \[ C_1 \times V_1 = C_2 \times V_2 \]
3. Rearrange the equation to solve for the initial concentration \( C_1 \): \[ C_1 = \frac{C_2 \times V_2}{V_1} \]
4. Substitute the known values into the equation, making sure the volumes are in the same units (both are in mL, so no conversion needed): \[ C_1 = \frac{0.15 \text{ M} \times 250.0 \text{ mL}}{25.0 \text{ mL}} \]
5. Calculate the value of \( C_1 \) using the substituted values to find the original concentration of the HCl solution before dilution.