Physical Pharmaceutics - 1
Unit-5
pH, Buffers and Isotonic Solutions
👉 Sorensen's pH Scale
• pH - Power of Hydrogen
• It is given by Sorensen, so it is also called as Sorensen's pH Scale
• p - (Potenz means Power) and H - (Hydrogen)
• pH defined as negative logarithms of the hydrogen ion concentration.
pH = -log (H+)
•The concentration of the hydrogen ion is a measure of it's acidity or basicity of a aqueous solution at a specific solution.
- Acidic solution have a higher relative number of H+ ion.
- Basic/Alkaline solution have a higher relative number of OH- ion.
• pH scale help to measure the acidity and basicity of any solution.
fig. Sorensen's pH scale
• The pH scale ranges from 0 to 14
• The scale start with a zero(0) pH indicates that the solution is strongly acidic, and end with fourteen(14) indicates that the solution is strongly alkaline (basic).
• The central point pH in the scale is seven(7) indicates the solution is neutral (neither acidic nor basic).
•three region :-
(0 to below 7) - Acidic
(Seven 7 ) - Neutral
(Above 7 to 14 ) - Basic/Alkaline.
👉 Determination of pH
• The pH value is determine by following method :-
i) pH Paper
ii) Electrometric method
iii) Colorimetric method
i) pH Paper
- For routine work pH of a solution is determined by pH paper.
- Take a one pH paper and dip into sample solution ( which we have to determine the pH ).
-then compare the pH paper color (which change in solution) with Standard pH Paper in which pH number is written with color.
-According to pH value we determined, that the solution is acidic or basic or neutral.
ii) Electrometric Method
- Apparatus is known as pH meter.
- It consist a voltmeter which connected with two electrodes :-
• Standard electrode - known as potential
• Reference (probe) electrode - which enclosed in a glass membrane that allow migration of H+ ions, and it contains reference solution of dilute HCL.
fig. Electrometric method
Working -
• The Electrodes ( both- Standard + reference) are dipped in the solution to be tested.
• If the solution's pH differ from probe solution's pH, then probe passes electric signals to a meter that display the reading in pH units.
• A change in temperature can cause an error in the pH reading. To prevent this, a temperature compensation resistance ( thermocompensator) include in a circuit and immersed in the solution.
iii) Colorimetric Method
• Take a colorimetric paper and dip into sample solution ( which we have to determine the pH ).
• Then obtained color is computed with the standard table of colorimetric.
•Then pH value is obtained according to their color.
• According to pH value we determined, that the solution acidic or basic or neutral.
To be continue.......
fig. Colorimetric method
• For Watch Video Click Below on Picture 👇👇
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