ATI TEAS (Test of Essential Academic Skills) Version 7ScienceMedium
A technician is preparing a solution for an experiment. They need to dilute a 2 M stock solution of hydrochloric acid (HCl) to a final concentration of 0.5 M in a total volume of 500 mL. What volume of the stock solution is required?
- A50 mL
- B250 mL
- C125 mL
- D100 mL
Show answer & explanationAnswer & explanation
Correct answer: C. 125 mL
This is a dilution problem, which can be solved using the formula M1V1 = M2V2. Given M1 = 2 M, V2 = 500 mL, and M2 = 0.5 M. We need to find V1. (2 M) * V1 = (0.5 M) * (500 mL) V1 = (0.5 M * 500 mL) / 2 M V1 = 250 mL / 2 V1 = 125 mL
Why the other options are wrong
- A. Incorrect calculation. This would be 0.25 M in 200 mL.
- B. Incorrect calculation. This would result in a final concentration of 1 M.
- D. Incorrect calculation. This would be 0.4 M in 500 mL.
Dilution Formula (M1V1=M2V2)
A formula used to calculate the volume or concentration of a solution before or after dilution, assuming the amount of solute remains constant.
- M1 = initial concentration, V1 = initial volume.
- M2 = final concentration, V2 = final volume.
- Units for volume must be consistent (e.g., both mL or both L).
Memory trick: Many Volumes Make Many Volumes.