Acidimetry
by Elaine Lai, DP2 Student, Class of 2026
In our recent chemistry practical experiment, my classmate and I carried out an acid-base titration to determine the concentration of an unknown sodium carbonate ( Na₂CO₃) solution. Titration is a technique used to identify the concentration of a solution by reacting it with another solution of accurately known concentration. In this experiment, we used hydrochloric acid (HCl) as the standard solution (1 M) and methyl orange as the indicator.
Acidimetry is not only used in school laboratories but is also essential in real industries. In the food and beverage sector, titration helps control acidity in products like vinegar, juices, yoghurt, and soft drinks, since acidity affects taste, safety, and shelf life. Environmental agencies use acidimetry to check the acidity of rainwater, wastewater, and industrial effluents, while water treatment facilities rely on pH control to ensure safe drinking water. Pharmaceutical companies also use precise titration to maintain the correct acidity of medicines, as pH influences stability and effectiveness. This experiment, therefore, mirrors the quality-control processes applied across many industrial fields.
To prepare for the titration, we ensured that all glassware was properly rinsed. The burette was washed first with distilled water and then with the HCl solution to prevent dilution errors. A pipette was used to transfer an exact 10 mL of the Na₂CO₃ solution into a conical flask, and a few drops of methyl orange indicator were added. This indicator is yellow in basic solutions and turns red when the solution becomes acidic, allowing us to visually identify the endpoint of the titration. We then slowly released HCl from the burette while swirling the flask, watching carefully for the permanent colour change signalling that all carbonate ions had reacted.
After carrying out three trials, we obtained an average titre of 0.9 mL. Using this value in our calculations, we determined that the concentration of the Na₂CO₃ solution was approximately 0.09 mol dm⁻³, while the theoretical concentration was 0.10 mol dm⁻³. This indicates a percentage error of roughly 10%. The endpoint was identified by the colour change from orange or yellow to red. One key improvement is ensuring all glassware is completely dry before starting, as leftover water can dilute the solutions. Handling the burette carefully would also help maintain consistency. Even so, our accuracy improved from 17% error to 10%, showing better control and technique.
To extend this experiment, we could repeat the titration with a different indicator, such as phenolphthalein, to compare endpoint accuracy. Testing several unknown carbonate samples would allow us to see how concentration affects precision. Using digital pH meters could minimize human error during endpoint detection, while investigating how temperature influences reaction rate and colour change would deepen our understanding of titration reliability. These extensions would strengthen our practical skills and connect our work further to real analytical chemistry practices.
