This document discusses pH and pH measurement. It defines pH as the negative log of hydrogen ion activity and explains that pH ranges from 0 to 14, with values below 7 being acidic and above 7 being basic. It describes how pH can be measured using a pH meter, which consists of a pH-sensitive glass electrode, reference electrode, and meter. Alternative measurement methods include pH paper (indicators) and digital pH meters. pH paper relies on color matching but is imprecise, while pH meters provide more precise readings but require rinsing and storing the electrode wet when not in use.

1. pH Meter
Presented by :
A.R. Deborah
I M. Sc. Applied Microbiology
Department of Microbiology
Sacred Heart College (Autonomous)
Tirupattur
Presented To :
Dr. K. Amala
Assistant Professor,
Department of Microbiology,
Sacred Heart College (Autonomous)
Tirupattur

2. pH
• pH is an abbreviation of the French word “pouvoir hydrogene” that represents “hydrogen power” and
was proposed by Danish scientist Soren Peter Lauritz Sorensen in 1909 in order to express the very
small concentrations of hydrogen ions.
• The pH is defined as the negative log of hydrogen ion activity. It does not indicates the hydrogen ion
concentration.
pH = - log (H+)
• pH is an important parameter because many of nature's processes are highly dependent on pH .
However, as most chemical and biological reactions are governed by the hydrogen ion activity.
• Every aqueous solution can be measured to determine its pH value. This value ranges from 0 to 14 pH.
Values below 7 pH exhibit acidic properties. Values above 7 pH exhibit basic (also known as caustic or
alkaline) properties. Since, 7 pH is the center of the measurement scale, it is neither acidic nor basic, it
is called "neutral."

3. pH MEASUREMENT:
pH in an aqueous solution can be measured in a variety of ways. The most common way uses a pH‐sensitive glass
electrode, a reference electrode and a pH meter.
Alternative methods for determining the pH of a solution are:
1) Indicators (pH Paper)
• Indicators are materials that are specifically designed to change color when exposed to different pH values.
• The color of a wetted sample paper is matched to a color on a color chart to infer a pH value.
• pH paper is available for narrow pH ranges.
• pH paper is typically used for preliminary and small volume measuring. It cannot be used for continuous
monitoring of a process.
• Though pH paper is fairly inexpensive, it can be attacked by process solutions, which may interfere with the
color change.

5. 2) pH (Digital meter)
• pH meter is an electronic instrument consisting of a special bulb that is sensitive to hydrogen
ions that are present in the test solution. The signal produced by the bulb is amplified and sent
to an electronic meter connected to the bulb, which measures and display the pH reading.
• After each single measurement, the bulb is rinsed with distilled water or deionized water to
remove any traces of solution being measured. Then the bulb is blotted with a blotting paper
to remove remaining water that could dilute the sample and alter the reading. When not in
use, the bulb must be kept wet at all times to avoid dehydration of the pH sensing membrane.
• pH meter gives more precise values than the pH papers.

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