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What is pH of Water? Methods of Determining pH of Water

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What is pH of Water?

pH of water is a measure of amount of hydrogen ions that is present in the water. It determines if the water is alkaline or acidic in nature. pH stands for potential of hydrogen. As per the World Health Organization (WHO), value of pH for the water is 6.5 to 8.5. pH can be calculated mathematically as

pH = -log [H]

This scale was developed by the scientist Sorenson in the year 1909. The below reaction implies that the water shows that the number of H+ and OH- ions are equal in amount experimentally. It has also been proved that the product of both the concentration is equal to a constant ‘K’. The value of this constant found to be between 10 and 14.

H2O –> H+ + OH-

For acids, the pH value is between 1 to 7. Alkaline will have pH value from 7 to 14.

Determination of pH of Water

There are two methods involved in the determination of pH value of water. They are:
  1. Colorimetric Method
  2. Electrometric Method
In environmental engineering experiments, every stage of water treatment is dependent on the pH value of the water. For example, the coagulation, disinfection, control of corrosion, acid-base neutralization and water precipitation.

Colorimetric Method for pH of Water

Take the pH standard solution and the water that is to be tested. Take the colorimetric paper. Dip this paper on the water sample. The obtained color is computed from the standard table and the respective pH value is recorded. This pH Value will conclude whether the sample of water is acidic or alkaline.

Fig.1. Standard pH Chart

Electrometric Method for pH of water

One of the most widely accepted method for the hydrogen ion determination (pH) is the electrometric method. This method is highly accurate and used in laboratory work and by researchers. The accuracy of the pH value is 0.1 to 0.0001.

Fig.1. Determination of pH of water by pH meter

Apparatus for pH Determination

The apparatus required for the determination of water pH are:

Procedure for pH Determination

The procedure of determination of pH of water involves the following steps:

Precautions and Tips

  1. The pH meter can be standardized by measuring the 7-pH buffer solution or any other solution of standard pH. Sometimes, the manufacturer of the pH meter may suggest other methods of standardizing, which too have to be followed.
  2. The electrodes have to be inserted into the water so that it does not touch the bottom of the beaker. Bottom contact with damage may cause damage to the electrodes.
  3. Any cause of slow response due to the polarization can be solved by washing the electrodes thoroughly.
  4. Periodic check has to be conducted to check the electrodes
  5. During the electrode storage, they have to be kept moist. And also follow the instructions of the manufacturer.
Read More: Characteristics of Water - Physical, Chemical and Biological Tests for Water Quality for Concrete Construction and Recommended Limits Quality of Water for Concrete Construction and its Specification
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