ATI TEAS (Test of Essential Academic Skills) Version 7ScienceMedium
A technician is preparing a solution of hydrochloric acid (HCl) by diluting a 12 M stock solution to a final concentration of 0.5 M. If the desired final volume is 250 mL, what volume of the concentrated stock solution is needed?
- A4.17 mL
- B5.21 mL
- C20.8 mL
- D10.4 mL
Show answer & explanationAnswer & explanation
Correct answer: D. 10.4 mL
Using the dilution formula M1V1 = M2V2, where M1 = 12 M, V1 = ?, M2 = 0.5 M, and V2 = 250 mL. Solving for V1: V1 = (M2V2) / M1 = (0.5 M * 250 mL) / 12 M = 125 / 12 = 10.416 mL. Rounded to one decimal place, this is 10.4 mL.
Why the other options are wrong
- A. 4.17 mL is incorrect; likely a calculation error or inverse operation.
- B. 5.21 mL is incorrect; likely a calculation error.
- C. 20.8 mL is incorrect; possibly doubling the correct value or another calculation error.
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 and V1 are initial molarity and volume.
- M2 and V2 are final molarity and volume.
- Units for volume must be consistent (e.g., both mL or both L).
Memory trick: Mighty Vials Make More Volume.