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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.
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