ACT (Enhanced)ScienceHard
A chemist is performing a titration to determine the concentration of an unknown acid. They record the initial volume of the titrant (0.50 mL), the final volume of the titrant (23.75 mL), and the concentration of the titrant (0.100 M). If the chemist calculates the volume of titrant used as 23.25 mL, but the actual volume delivered by the burette was 23.35 mL due to a slight parallax error during reading, how would this error affect the calculated concentration of the unknown acid?
- AThe calculated concentration would be accurate if the error was consistent.
- BThe calculated concentration would be higher than the actual concentration.
- CThe calculated concentration would be lower than the actual concentration.
- DThe calculated concentration would be unaffected.
Show answer & explanationAnswer & explanation
Correct answer: C. The calculated concentration would be lower than the actual concentration.
If the calculated volume of titrant used (23.25 mL) is less than the actual volume delivered (23.35 mL), it means the chemist underestimated the amount of titrant needed. Since the concentration of the unknown acid is directly proportional to the volume of titrant used (M1V1 = M2V2), underestimating V2 (titrant volume) will lead to an underestimation of M1 (unknown acid concentration).
Why the other options are wrong
- A. Consistency in error (systematic error) allows for correction, but if uncorrected, it still leads to an inaccurate result. The question implies an uncorrected error.
- B. This would happen if the calculated volume was *greater* than the actual volume.
- D. The error directly impacts the volume measurement, which is a critical component of the concentration calculation.
Propagated Error (Titration)
The way in which errors in measured quantities (like volume in titration) affect the accuracy of a calculated result (like concentration).
- Errors can be systematic or random.
- Titration relies on precise volume measurements.
- Underestimating volume of titrant leads to underestimating unknown concentration.
Memory trick: Small measurement error, big calculation difference.