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# The Concept and importance of pH Scale

May 29, 2018 11:29 IST
What is pH scale

pH stands for 'potential of Hydrogen' which measure the acidity or alkalinity of water soluble substances. It is measured with a logarithmic scale known as pH. In 1909, a danish biochemist S.P.L Sorenson devised a scale pH to represents the H+ ion concentration of an aqueous solution.
Do you know what is acid and base?
An acid is a substance that donates hydrogen ions that is when in a solution there are more hydrogen ions than hydroxide ions, the solution will be acidic.
A base is a substance that accepts hydrogen ions that is when in a solution there are more hydroxide ions than hydrogen ions, the soulution will be alkaline.
The pH value of any solution is numerically equal to the logarithm of the inverse of the hydrogen ion (H+) concentration. Hence, the pH of solution is referred to as the negative logarithm of hydrogen ion.

pH = -log [H+]

= log 1/ [H+]

Basic concept of pH value

• pH of Neutral Solution (Pure Water): pH of water is 7. Whenever the pH of a solution is 7, it will be a neutral solution. Such a solution will have no effect on any litmus solution or any other indicator.
• pH of an Acidic Solution: All the acidic solutions have a pH less than 7. So, whenever a solution has a pH less than 7, it will be acidic in nature and it will turn blue litmus into red as well as methyl orange pink and phenolphthalein colourless.
• pH of a basic solution: All the alkaline solution have a pH of more than 7. So, whenever a solution has more than 7 values then it will be basic in nature and it will turn red litmus to blue, methyl orange to yellow and phenolphthalein to pink.

Source: www.kangensui.us

 pH values of the common substance from our daily life Solution pH Solution pH Conic HCl Saliva (before meal) 7.4 Oil HCl 1.0 Saliva (after meal) 5.8 Gastric Juice 1.4 Blood 7.4 Lemon Juice 2.5 Eggs 7.8 Vinegar 4.0 Toothpaste 8.0 Tomato Juice 4.1 Baking Soda Solution 8.5 Coffee 5.0 Washing Soda Solution 9.0 Soft Drink 6.0 Milk of Magnesia 10.5 Milk 6.5 Household Ammonia 11.6 Pure Water 7.0 Dilute Sodium Hydroxide 13.0 Concentrated Sodium Hydroxide 14

Things to remember about pH Value and concentration

• An acid solution having low pH is stronger than another solution having higher pH values. A solution having pH of 2 is a stronger than a solution having pH of 5.
• An alkali solution having higher pH value is a stronger than a solution of pH 10.
•  Very Strong acids solution can have pH values less than zero and very strong basic solutions can pH greater than 14.

Universal Indicator of colour at pH scale

It is a mixture of different indicators (or dyes) which gives different colours at different pH values of the entire pH scale. The colour produced by universal indicators at various pH values are given in the table below:

 Colour pH Colour pH Dark Red Greenish Yellow 8 Red 1 Blue 9 Red 2 Navy Blue 10 Orange Red 3 Purple 11 Orange 4 Dark Purple 12 Orange Yellow 5 Violet 13 Greenish Yellow 6 Violet 14 Green 7

Importance of pH

• In Agriculture: By determining the pH of the soil. We can find whether it is acidic or alkaline. This helps in deciding the type of fertilizer to be used and the types of crops to sown.
• In Biological process: By knowing pH we can adjust the medium of biological processes like fermentation, enzyme hydrolysis, sterilization etc.
• In corrosion research: By measuring the pH of sea-water, the effect of alkaline sea-water on the material used for building ships and submarines is studied.

Buffer Solution

A Buffer Solution or a buffer is defined as a solution whose pH does not change when small amount of an acid or base is added in it. It is used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. Many life forms thrive only in a relatively small pH range so they utilize a buffer solution to maintain a constant pH. In nature, the bicarbonate buffering system is used to regulate the pH of blood. The solution of Sodium Acetete and Acetic acid is an example of an effective buffer solution. The solution in which buffer solution is accomodated that works like an extremely slow acid.

How Ionic Compounds are formed?

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