Accurate pH measurement is essential in laboratories, industry, and research.
Electrometric Methods
Principle:
Based on the measurement of the electromotive force (EMF) of a galvanic cell that includes a pH-sensitive electrode.
Components:
Glass Electrode: Sensitive to hydrogen ion activity; develops a potential proportional to pH.
Reference Electrode: Provides a constant potential; commonly a silver/silver chloride or calomel electrode.
pH Meter: Reads the potential difference and displays the pH.
Procedure:
Calibrate the pH meter using standard buffer solutions of known pH.
Rinse electrodes with distilled water.
Immerse electrodes in the test solution.
Record the stable pH reading.
Advantages:
High accuracy and precision.
Suitable for a wide pH range.
Can measure pH in colored or turbid solutions.
Applications:
Research laboratories.
Quality control in manufacturing.
Clinical diagnostics.
Colorimetric Methods
Principle:
Utilize pH indicators that change color depending on the pH of the solution.
Indicators:
Weak acids or bases with different colors in protonated and deprotonated forms.
Common indicators include litmus, phenolphthalein, methyl orange, and bromothymol blue.
Procedure:
Add a few drops of indicator to the test solution.
Observe the color change.
Compare the color to a standard pH color chart.
Advantages:
Simple and cost-effective.
Quick estimation of pH.
Limitations:
Less precise than electrometric methods.
Subjective interpretation of color.
Not suitable for colored or opaque solutions.
Applications:
Educational demonstrations.
Field testing where equipment is unavailable.