ACT (Enhanced)MathematicsHard
A chemist is preparing a solution. She needs to dilute a 25% acid solution to a 5% acid solution. If she has 200 mL of the 25% solution, how much water (in mL) must she add to achieve the desired concentration?
- A200 mL
- B800 mL
- C400 mL
- D600 mL
Show answer & explanationAnswer & explanation
Correct answer: B. 800 mL
Use the dilution formula M1V1 = M2V2. First, find the final volume (V2). Then, subtract the initial volume (V1) from V2 to find the amount of water to add.
Why the other options are wrong
- A. This is the initial volume, not the amount of water added.
- C. This results from a calculation error, possibly dividing by 2 instead of 5.
- D. This results from subtracting the final volume from the initial volume incorrectly.
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 of concentration and volume must be consistent on both sides.
Memory trick: M1V1 is M2V2, then subtract the start, what's new?