Determination of pH (potentia Hydrogen) of water

The determination of pH is the most frequently used test in water chemistry.So all students must learn how to test pH of water for various purpose in their life irrespective of their branches.

Practically every phase of water and waste water treatment is pH dependent. pH is used in alkalinity and Co2 measurements and in many other acid-base equilibria.

Principle of ph of water

pH is the negative logarithm of Hydrogen ion concentration in a liquid. According to the law of mass action,Concentration of H+ ions X Concentration of OH- ions = a constant = 10-14 Concentration of undissociated HOH molecules

Determination of ph
Determination of ph in water

For convenience pH is taken from 0 to 14. The neutral water has a pH = 7. From pH 0 to 7, the water is said to be acidic and thereafter it is said to be alkaline.

The basic principle of electrometric pH determination is the measurement of activity of Hydrogen ions by potentiometric measurements using a standard hydrogen electrode and a reference electrode.

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pH is measured by a pH meter using a glass electrode which generate a potential varying linearly with the pH of the solution in which it is immersed. It is a Nerstrian concentration cell, with potential controlled by the activities of H+ ions on either side of a thin glass membrane.

A calomel or Ag/AgCl/KCl reference electrode is usually located around the glass electrode stem for sample operation.The reagents used are distilled water, buffer solution of pH 4.0,buffer solution of pH 7.0 and buffer solution of pH 9.2.

Reagents:

  1. Distilled water
  2. Buffer solution of pH 4.0
  3. Buffer solution of pH 7.0
  4. Buffer solution of pH 9.2

Procedure for how to test ph of water

  1. Standardize the pH meter as per the directions given by the manufacturer’s manual using buffer solutions of pH 4.0, 7.0 and 9.2.
  2. Clean the electrode using distilled water and wipe off.
  3. Insert the electrode in the sample. Wait for a steady reading. Note the pH.The reading will get directly from ph meter.
  4. Temperature of the sample is noted.

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The below video shows how to determine ph of water

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