The PH Scale is a measure of the strength of an acid or base. The PH of a solution is measured using a paper impregnated with a universal indicator.
In the previous articles, we have learned that acids produce hydrogen or hydronium ions in a solution. The strength of an acid is proportional to the concentration of the hydronium ions. Therefore, if we have a way to measure the concentration of hydronium ions, then we would be able to quantify the strength of an acid. Similarly, the strength of a base is directly proportional to the concentration of the hydroxide (OH) ions.
The PH Scale is the log of the hydronium ion concentration. An acid is any substance whose hydronium ion concentration is more that 10-7 moles/litre. Therefore, an acid will always have a PH of less than 7. As the strength of the acid increases, the PH decreases. For example, lemon juice has a PH for 2.3. The hydrochloric acid in our stomachs has a PH of 1.5-2, and the PH of concentrated hydrochloric acid is nearly 0.
The PH scale is also used to measure the strength of bases. In general, bases have a PH greater than 7. Stronger the base, more is its PH. The maximum value possible on the PH scale is 14. A concentrated solution of sodium hydroxide would have a PH value of 14.
So, what is the importance of the PH scale in the everyday file?
Most life processes can occur within a narrow range of PH. For example, the PH of blood is tightly regulated in the range of 7.2 to 7.4. Similarly, the PH value of the soil is of great importance in agriculture. Most food crops grow best at a PH of 7-7.8. The growth of plants suffers when the PH value is outside this range. The PH of soil is usually tightly regulated by the microflora present in the ground. However, excessive use of ammonia-based fertilisers can make the soil acidic.
Have you heard of acid rain? The atmosphere contains gasses like nitrous oxide and sulphur oxide. When these dissolve in rain, they produce nitric and sulphuric acid. If the concentration of these acids in high in rainwater, it can lower the PH value. Acid rain has a value of less than 5.6 on the PH scale. ?Acid rain is another cause of the increase in soil acidity.
The PH scale plays a critical role in the human body. Different parts of the human body have different PH. The mouth has a slightly alkaline PH while the stomach has a very acidic PH. The skin has a slightly acidic PH, and the PH in the Vagina is again very acidic. Why is this so?
The saliva in the oral cavity makes the PH of the mouth alkaline. The alkaline PH facilitates the action of salivary enzymes. It also prevents tooth decay. Why do we wash our mouth after eating anything? The sugars present in the food can ferment to produce acid. This acid can damage the enamel of the teeth, thus causing tooth decay.
The PH of the stomach is between 1.3 -2. The glands in the stomach secrete a hydrochloric acid that makes the PH of the stomach acidic. The acidic PH serves two functions- it kills any microorganisms, and it facilitates the action of enzymes like trypsin.
Similarly, the acidic PH of the skin and vagina prevent colonisation by bacteria, thus serving as a natural defence against infection.
Thus, the PH scale plays a crucial role in everyday life. Students are frequently asked to calculate the PH in the board exams. Therefore, the PH scale is an important topic that the students of class 10 science should master.
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