The mathematical foundation of titration is based on the mole concept and the relationship , where is the number of moles, is the concentration in , and is the volume in .
During the reaction, the stoichiometry of the balanced equation dictates the ratio in which the reactants combine; for a 1:1 reaction, the moles of acid will equal the moles of base at the equivalence point.
For reactions with different ratios, such as , the calculation must account for the 1:2 molar ratio to find the correct concentration.
Indicators are weak acids or bases that change color at specific pH ranges; the choice of indicator depends on the expected pH at the equivalence point of the specific acid-base pair being titrated.
| Feature | Equivalence Point | End Point |
|---|---|---|
| Nature | Theoretical/Stoichiometric | Experimental/Observable |
| Detection | Calculated via stoichiometry | Signaled by indicator color change |
| Accuracy | Represents the exact reaction completion | Approximation of the equivalence point |
Pipette vs. Burette: A pipette is designed to deliver a single, fixed volume (e.g., ) with high accuracy, whereas a burette is designed to deliver variable volumes that can be measured to the nearest .
Universal vs. Specific Indicators: Universal indicator is unsuitable for titrations because it undergoes a gradual color change over a wide pH range, whereas specific indicators like phenolphthalein provide a sharp, distinct color change at the end point.
Reading the Meniscus: Always read the volume from the bottom of the curve (meniscus) at eye level to avoid parallax errors and ensure consistent measurements.
Calculating the Mean: When calculating the average titre, only include concordant results; the rough titration should be excluded unless it happens to be concordant with the precise runs.
Unit Conversion: Ensure all volumes are converted from to (by dividing by ) before using them in concentration formulas to avoid magnitude errors.
Sanity Check: If the volume of titrant required is significantly different from the rough run or previous trials, check for errors like air bubbles in the burette tip or incorrect indicator choice.
The Funnel Error: Leaving the funnel in the top of the burette after filling can lead to extra drops falling in during the titration, which artificially increases the recorded volume.
Air Bubbles: Failing to remove air bubbles from the burette tip before starting results in an inaccurate volume reading, as the bubble volume is counted as titrant delivered.
Over-titrating: Adding titrant too quickly at the end point can lead to 'overshooting' the color change, resulting in a calculated concentration that is higher or lower than the true value.
Swirling and Rinsing: Not swirling the flask or failing to rinse the sides with distilled water can leave unreacted droplets on the glass, leading to an inaccurate end point.
