What is the molar concentration of the chloride ion (Cl⁻) in a solution prepared by diluting 25.0 mL of a 0.100 M CaCl₂ solution to a final volume of 250 mL?

• A. 0.010 M
• B. 0.020 M
• C. 0.050 M
• D. 0.040 M

Answer: (B)

Verified step by step guidance

1. Identify the initial concentration and volume of the CaCl₂ solution. The initial concentration is 0.100 M and the initial volume is 25.0 mL.
2. Calculate the number of moles of CaCl₂ in the initial solution using the formula: \( \text{moles} = \text{concentration} \times \text{volume} \). Convert the volume from mL to L by dividing by 1000.
3. Determine the number of moles of Cl⁻ ions produced. Since each molecule of CaCl₂ dissociates into one Ca²⁺ ion and two Cl⁻ ions, multiply the moles of CaCl₂ by 2 to find the moles of Cl⁻.
4. Calculate the final concentration of Cl⁻ ions after dilution. Use the formula: \( \text{final concentration} = \frac{\text{moles of Cl⁻}}{\text{final volume in L}} \). Convert the final volume from mL to L by dividing by 1000.
5. Verify the calculation by ensuring the units are consistent and the stoichiometry of the dissociation reaction is correctly applied.