Understanding pH: Measurement and Meter

Study Notes

The pH of a solution is the negative logarithm of the hydrogen ion concentration.
pH is a scale from 0 to 14, where below 7 is acidic and above 7 is alkaline.
Neutral pH is 7.

Two main methods are used: Paper strip method and Electrometric Method (pH meter).
The paper strip method uses strips that change color in response to different pH values. This method provides only a general estimation of pH and is not very precise.
The electrometric method uses a pH meter, which offers a more accurate reading of pH.

The pH meter uses an electrode that is sensitive to hydrogen ions.
The meter measures the voltage difference between the reference electrode and the pH electrode to determine hydrogen ion concentration.
The pH meter needs to be calibrated with solutions of known pH before any measurements are taken.

A glass electrode is used, containing a silver wire coated in AgCl paste which is dipped in 0.1 NHCl.
This serves as the internal reference electrode.

A pH measuring electrode (glass electrode) measures the acidity of a sample based on the number of H+ ions.
A reference (calomel) electrode does not change with the activity of hydrogen ions and has a fixed pH.

Turn on the meter.
Rinse the electrode with distilled water.
Set the temperature knob to room temperature if available.
Calibrate the meter using a pH 7 buffer standard.
Rinse the electrode with distilled water again, being careful not to damage the tip.
Place the electrode in the solution you want to test.
Swirl the solution until the pH display stops changing.
Note the pH reading.
If the solution is very acidic or basic, use a pH 4 buffer (acid) or a pH 10 buffer (base) to slope the meter after calibrating it with pH 7.

Enzymatic reactions in all living organisms occur at a specific pH.
Soil pH is important for the growth of crops.
Blood pH is maintained within a normal range through homeostasis, and pH determination is crucial for diagnosing and monitoring acid-base imbalances.
pH is used in industries like leather and food processing.