What Is Difference Between Potentiometric Titration and Indicator Type Titration?

What Is Indicator Type Titration?

This is the traditional form of titration, where a chemical indicator is used to signal the endpoint of the titration. The indicator changes color based on the pH (or another property like redox potential) of the solution, signaling that the equivalence point has been reached.

• How it works:
  • You add a titrant (usually a strong acid or base) to the analyte (sample solution), and the indicator responds to changes in the properties (e.g., pH) of the solution.
  • When the endpoint is reached, the indicator changes color, and you can stop adding the titrant.
• Pros:
  • Simple and easy to perform.
  • Widely used for acid-base titrations, redox titrations, etc.
  • Inexpensive equipment.
• Cons:
  • Not suitable for all types of titrations (e.g., when the pH change is too subtle or the reaction is slow).
  • The endpoint is not always sharp or clear.
  • The choice of indicator is crucial and can introduce errors.
• Example:
  • Acid-base titration using phenolphthalein as an indicator. It changes from colorless to pink at the endpoint (usually around pH 7 for a strong acid and base).

What Is Potentiometric Titration?

In this method, the potential (voltage) of the solution is measured continuously throughout the titration. This is done using a pH electrode (or other suitable electrode) to measure the potential as the titrant is added. The endpoint is determined when there is a significant change in the potential.

• How it works:
  • A known volume of the sample solution is titrated with a titrant.
  • The potential (voltage) is measured with an electrode (e.g., pH meter for acid-base titrations or a redox electrode for redox titrations).
  • A graph of the potential vs. the volume of titrant added is plotted, and the endpoint is indicated by a sudden change in the slope of the curve.
• Pros:
  • More accurate and precise than indicator-based titration.
  • Can be used for a wider range of titrations, including those with subtle pH changes.
  • Less reliance on the choice of indicator, so it is less prone to errors.
  • Ideal for reactions where no clear color change occurs.
• Cons:
  • Requires more sophisticated equipment (pH meter or potentiometer).
  • Can be more expensive and time-consuming.
  • Requires some expertise in interpreting the titration curve.
• Example:
  • Acid-base titration using a pH meter to track the potential. The equivalence point is detected by a sharp change in pH, corresponding to the inflection point of the titration curve.

What Is Difference Between Potentiometric Titration and Indicator Type Titration?

Case Study: Determination of the concentration of Acetic Acid (CH₃COOH) in Vinegar

Background:

Vinegar contains acetic acid (CH₃COOH), a weak acid, dissolved in water. The concentration of acetic acid in vinegar can vary, and it is important to know the concentration to ensure quality control in food products. This experiment uses potentiometric titration with a strong base (sodium hydroxide, NaOH) to determine the acetic acid concentration accurately.

Objective: Determine the concentration of acetic acid in a vinegar sample using a potentiometric titration technique with NaOH as the titrant.

Experimental Setup:

1. Apparatus and Reagents:
   • Burette – to contain the NaOH solution.
   • Beaker – to hold the vinegar sample (acetic acid solution).
   • pH Electrode – to measure the pH of the solution.
   • pH Meter – to monitor the change in pH during titration.
   • NaOH Solution – standard solution of known concentration (e.g., 0.1 M).
   • Vinegar Sample – a known volume of vinegar with an unknown concentration of acetic acid.
2. Procedure:
   • Step 1: Measure a known volume (e.g., 25.00 mL) of the vinegar sample and pour it into a beaker.
   • Step 2: Calibrate the pH meter with standard buffer solutions (pH 4.00, 7.00, and 10.00).
   • Step 3: Insert the pH electrode into the vinegar solution and record the initial pH.
   • Step 4: Slowly titrate the vinegar solution with the NaOH solution from the burette while continuously stirring the solution.
   • Step 5: Record the pH after every fixed amount of NaOH added (e.g., 0.5 mL increments).
   • Step 6: Plot the pH values on the y-axis against the volume of NaOH added on the x-axis.

Results and Data Analysis:

As the titration progresses, the pH of the vinegar will increase gradually as NaOH is added. Initially, the pH will rise slowly, but as the endpoint (equivalence point) approaches, the pH will begin to increase rapidly.

Key Points on the Titration Curve:

1. Initial pH: The initial pH of vinegar (acetic acid solution) will be slightly acidic, typically around pH 2-3.
2. Buffer Region: As NaOH is added, acetic acid will react with NaOH to form water and acetate ions. During this phase, the pH increases gradually, but not sharply. This is because acetic acid is a weak acid and its dissociation is buffered.
3. Equivalence Point: The equivalence point will be identified as the steepest part of the curve, where there is a sharp rise in pH. For acetic acid, the equivalence point will be slightly basic, around pH 8.5 to 9 (because the acetate ion (CH₃COO⁻) is a weak base).
4. Post-Equivalence Point: After the equivalence point, the pH will rise slowly as excess NaOH is added.

Determining the Equivalence Point:

By analyzing the titration curve, you can find the equivalence point by locating the steepest slope, or by calculating the inflection point (where the change in pH per unit volume of NaOH is greatest). This is where all the acetic acid has reacted with NaOH, and any further addition of NaOH will result in a rapid increase in pH.

Calculation:

Once the equivalence point is determined, you can calculate the concentration of acetic acid in the vinegar sample using the formula:

Let’s assume the following data:

• Volume of vinegar sample: 25.00 mL
• Volume of NaOH used at equivalence point: 27.50 mL (0.0275 L)
• Molarity of NaOH: 0.1 M

Molarity of Acetic Acid = (0.1mol/L × 0.0275L)/0.025L = 0.11M

Thus, the concentration of acetic acid in the vinegar is 0.11 M

Conclusion

Potentiometric titration is typically preferred for more precise, automated, and complex titrations, while indicator titrations are simpler, cheaper, and widely used for routine analysis, especially when the endpoint is clearly visible with a color change.

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