`color{green}(★)` Strength of acids and bases depends on the no. of `color{red}(H^+)` ions and `color{red}(OH^–)` ions produced respectively.

`color{green}(★)` With the help of a universal indicator we can find the strength of an acid or base. The universal indicator shows different colours at different concentrations of hydrogen ions in a solution.

`color{green}(★)` A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. The p in pH stands for ‘potenz’ in German, meaning power. On the pH scale we can measure pH generally from 0 (very acidic) to 14 (very alkaline).

`color{green}(★)` pH should be thought of simply as a number which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration, lower is the pH value.

`color{green}(★)` The pH of a neutral solution is 7. Values less than 7 on the pH scale represent an acidic solution. As the pH value increases from 7 to 14, it represents an increase in `color{red}(OH^–)` ion concentration in the solution, that is, increase in the strength of alkali (Fig. 2.6). Generally paper impregnated with the universal indicator is used for measuring pH.



Strong Acids give rise to more `color{red}(H^(+))` ions .

`color{red}(Eg. \ \ HCl , H_2SO_4 )` and `color{red}(HNO_3)`.

Weak Acids give rise to less `color{red}(H^(+))` ions.

`color{red}(Eg. \ \ CH_3COOH , H_2CO_3 ("Carbonic acid"))`

Strong Bases - Strong bases give rise to more `color{red}(OH^(-)) ` ions .

`color{red}(Eg.\ \ NaOH , KOH , Ca(OH)_2)`

Weak Bases ; gives rise to less `color{red}(OH^(-))` ions .

`color{red}(Eg. \ \ NH_4OH)`

`color{green}(★)` Our body functions between the range of 7.0 to 7.8 living organisms can survive only in the narrow range of pH change.

`color{green}(★)` Importance of pH in our digestive system – pH level of our body regulates our digestive system. In case of indigestion our stomach produces acid in a very large quantity because of which we feel pain and irritation in our stomach. To get relief from this pain antacids are used. These antacids neutralises the excess acid and we get relief. Magnesium hydroxide (Milk of magnesia), a mild base, is often used for this purpose.

`color{green}(★)` 𝐩𝐇 𝐨𝐟 𝐀𝐜𝐢𝐝 𝐑𝐚𝐢𝐧 : When pH of rain water is less than 5.6 it is called Acid Rain. When this acidic rain flows into rivers,the pH of river water lowers , which causes a threat to the survival of aquatic life.

`color{green}(★)` 𝐩𝐇 𝐨𝐟 𝐒𝐨𝐢𝐥 : Plants require a specific range of pH for their healthy growth. If pH of soil of any particular place is less or more than normal than the farmers add suitable fertilizers to it.

`color{green}(★)` 𝐓𝐨𝐨𝐭𝐡 𝐝𝐞𝐜𝐚𝐲 𝐚𝐧𝐝 𝐩𝐇 : Tooth enamel, made up of calcium phosphate is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Tooth decay starts when the pH of the mouth is lower than 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes being basic in nature are used for neutralizing the excess acid and prevent tooth decay.

`color{green}(★)` Bee sting or Nettle sting contains methanoic acid which causes pain and irritation. Use of a weak base like baking soda provides relief.


`color{red}("𝐉𝐔𝐒𝐓 𝐅𝐎𝐑 𝐂𝐔𝐑𝐈𝐎𝐔𝐒")`

`color{green}(★)` The atmosphere of venus is made up of thick white and yellowish clouds of sulphuric acid. Do you think life can exist on this planet?

`color{green}(★)` Nettle is a herbaceous plant which grows in the wild. Its leaves have stinging hair, which cause painful stings when touched accidentally. This is due to the methanoic acid secreted by them. A traditional remedy is rubbing the area with the leaf of the dock plant, which often grows beside the nettle in the wild. Can you guess the nature of the dock plant? So next time you know what to look out for if you accidentally touch a nettle plant while trekking. Are you aware of any other effective traditional remedies for such stings?