The document discusses measuring pH using a pH meter. A pH meter uses a bulb sensitive to hydrogen ions to measure the pH of a solution. The pH meter gives a more precise reading than pH strips or indicators. For accurate readings, the pH meter must be calibrated with buffer solutions of known pH, such as pH 4 and pH 10, before each use. The bulb must also be rinsed with distilled water between measurements and kept wet when not in use. The document also defines a colloid as a mixture with dispersed particles between 1 and 1000 nanometers that remain evenly mixed throughout the solution.

1. Physiochemical principles
Senior Lecturer
UIMLT, FAHS
2nd Lecture

2. pH and its determination
How to measure the PH of a solution ?
pH of a solution is measured by using following:
pH strips
pH indicators
pH meter

3. pH meter is an electronic instrument consisting of a special bulb that
is sensitive to hydrogen ions, 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.
It gives more precise values than the pH papers.
pH meter

5. For very precise measurement, the pH meter should be calibrated
before each measurement.
The calibration should be performed with at least two buffer solutions
with known pH.
For general purposes, buffer solutions with pH 4 and pH 10 are
used. For more precise measurements, three buffer solution
calibrations are preferred.

6. 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.

7. The colloidal state
A colloid is one of the three primary types of mixtures, with the other
two being a solution and suspension.
A colloid is a solution that has particles ranging between 1 and 1000
nanometers in diameter, yet are still able to remain evenly
distributed throughout the solution. These are also known as colloidal
dispersions because the substances remain dispersed and do not settle
to the bottom of the container.

8. In colloids, one substance is evenly dispersed in another.
Depending on the degree of dispersion, the systems are classified as:
True solution
Colloidal solution
Suspension