ATI TEAS (Test of Essential Academic Skills) Version 7ScienceMedium
A chemist needs to prepare 500 mL of a 0.25 M solution of sodium chloride (NaCl) from a 2.0 M stock solution. What volume of the stock solution is required?
- A62.5 mL
- B250 mL
- C500 mL
- D125 mL
Show answer & explanationAnswer & explanation
Correct answer: A. 62.5 mL
Using the dilution formula M1V1 = M2V2, where M1 = 2.0 M, V1 = unknown, M2 = 0.25 M, V2 = 500 mL. Solving for V1: V1 = (M2 * V2) / M1 = (0.25 M * 500 mL) / 2.0 M = 125 M·mL / 2.0 M = 62.5 mL.
Why the other options are wrong
- B. This would be the answer if the target molarity was 1.0 M.
- C. This would mean no dilution occurred or the stock solution was already 0.25 M.
- D. This would be the answer if the target molarity was 0.5 M.
Dilution Formula (M1V1=M2V2)
A mathematical equation used to calculate the volume or concentration of a solution when it is diluted. M1 and V1 are the initial molarity and volume, and M2 and V2 are the final molarity and volume.
- Molarity (M) is moles of solute per liter of solution.
- Volume (V) can be in liters or milliliters, as long as units are consistent.
- Assumes the amount of solute remains constant during dilution.
Memory trick: Mighty Vials Make More Volume.