Acidity and alkalinity of Hydrogen and its pH


All the chemicla substances based on their acidity ot alkalinity are given a rating called pH. pH or potential of hydrogen rating gives the measure of acidic or basic  nature of  the solution . In scientific terms it is explained as, pH is negitive logarithm of hydrogen-ion concentration in gram atoms per liter. The pH has a scale from 0 to 14, 7 being the center of the scale so a reading of 7 will mean the solution is neutral. The pH of pure water is exactly 7 (at 25 °C) which is neutral in nature. If the pH value of a substance is in between 0-7 it an acidic. If the pH value is greater than 7 it is alkali or base. 


The decrease in the pH value increases acidic nature, making it a strong acid. Automobile battery acid is an example of strong acid. Similarly increase in the pH value increases the basic nature, lye used in drain cleaners is a very alkaline chemical.


Why is  pH scale necessary?

pH measurement is must for all processes containing water. Most living things depend on a proper pH level to sustain life. For example,all animals and human beings rely on internal mechanisms to maintain the pH level of their blood. The blood flowing through our veins must have a pH between 7.35 and 7.45. Any increase in the pH levels could prove fatal. The pH of soil  plays an important role in improving the productivity of the crop. To attain high crop yields, farmers must condition their fields to the correct pH value.


Acid rain can be damage crop yields. pH of rain water  is typically around 5.6 but, in some areas, it increases to harmful levels ranging from  4.0 and 5.0 pH due to atmospheric pollutants. pH control prevents milk from turning sour and also prevents shampoo from stinging your eyes.  


 pH applications also include:

  • Neutralization of effluent in steel, pulp and paper, chemical, and pharmaceutical manufacturing
  • Hexavalent chromium destruction
  • Cyanide destruction
  • Odor scrubbers
  • Pharmaceutical manufacturing
  • Chemical and petrochemical manufacturing
  • Cooling tower control
  • Controlling Water run-off from coal mining operations
  • Food Processing, to neutralized waste material


How is pH measured?

To measure pH, hydrogen ion concentration must be determined. This is a tedious process. The alternative method to measure pH is to use colour indicators such as methyl violet, Congo red, methyl red, phenol red, litmus and phenolphthalein. These 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 standerd color chart to infer a pH value.


Devices such as Colorimeter are also used to measure pH. This colorimeter uses a vial filled with an appropriate volume of sample, to which a reagent is added. Addition of reagent results in a color change. The color of this solution is then compared to a color wheel or spectral standard to interpolate the pH value. The pH is also measured by using pH meters. This pH meters are consist of electrodes that generate electrical potentials depending on the pH specimen. These potentials are analysed by elcetrical circuritry to give the pH value.