Chemical Laboratory Report
Title: Acid–Base Titration of an Unknown Acid
Name: ____________________
Course: __________________
Instructor: ______________
Date: ____________________
Abstract
The purpose of this experiment was to determine the concentration of an unknown monoprotic
acid using acid–base titration. A standardized sodium hydroxide (NaOH) solution was used as
the titrant, and phenolphthalein served as the indicator. The endpoint was identified by a
persistent color change, allowing calculation of the acid’s molarity. The results demonstrate the
effectiveness of titration as a quantitative analytical method.
Introduction
Acid–base titration is a common analytical technique used to determine the concentration of an
unknown solution. This method relies on a neutralization reaction between an acid and a base.
When stoichiometric equivalence is reached, the amount of titrant added can be used to calculate
the concentration of the unknown solution. Phenolphthalein is often used as an indicator because
it exhibits a clear color change near the equivalence point.
Materials and Methods
Materials
•
•
•
•
•
•
Burette
Pipette
Erlenmeyer flask
Sodium hydroxide (0.100 M)
Unknown acid solution
Phenolphthalein indicator
Procedure
1. The burette was rinsed and filled with standardized NaOH solution.
2.
3.
4.
5.
6.
A measured volume of the unknown acid was pipetted into an Erlenmeyer flask.
Two drops of phenolphthalein were added to the acid solution.
NaOH was slowly added until a faint pink color persisted for 30 seconds.
The volume of NaOH used was recorded.
The titration was repeated for accuracy.
Results
Trial Volume of Acid (mL) Volume of NaOH (mL)
1
25.0
23.4
2
25.0
23.6
3
25.0
23.5
Average volume of NaOH used: 23.5 mL
Calculations
Using the balanced equation:
[
\text{NaOH} + \text{HA} \rightarrow \text{NaA} + \text{H}_2\text{O}
]
[
M_{\text{acid}} = \frac{M_{\text{NaOH}} \times V_{\text{NaOH}}}{V_{\text{acid}}}
]
Calculated molarity of unknown acid: 0.094 M
Discussion
The results obtained were consistent across all trials, indicating good experimental technique.
Minor sources of error may include endpoint detection and measurement inaccuracies. Overall,
the calculated concentration aligns with expected theoretical values.
Conclusion
The concentration of the unknown acid was successfully determined using acid–base titration.
This experiment demonstrates the reliability of titration as a method for quantitative chemical
analysis.
References
1. Brown, T. L., et al. Chemistry: The Central Science. Pearson Education.
2. Laboratory Manual, Department of Chemistry.