In 1909 Sorenson devised a scale known as pH scale to measure the strength of acid solutions as well as basic solutions, could be represented by making use of hydrogen ions concentration in the sample. pH scale has value from 0 to 14.
pH has no unit.
Rules Of pH Value:
- Neutral substance has the pH of exactly 7. e.g. Pure water is neutral in nature it has the pH 7.
- Acidic substance has the pH less then 7 because the pH value will decrease with the increase in the conc. of hydrogen ion
- Basic substance has the pH more then 7 because of less concentration of hydrogen ion in it.
pH and Corresponding color and strength of Solution
|0||Dark Red||Strong Acid||8||Greenish Blue||Weak Base|
|1||Red||Strong Acid||9||Blue||Weak Base|
|2||Red||Strong Acid||10||Navy Blue||Weak Base|
|3||Orange Red||Strong Acid||11||Purple||Strong Base|
|4||Orange||Weak Acid||12||Dark Purple||Strong Base|
|5||Orange yellow||Weak Acid||13||Violet||Strong Base|
|6||Greenish Yellow||Weak Acid||14||Violet||Strong Base|
Some common substance, their pH value and their corresponding colors
|Conc. Hydrochloric Acid||0||Dark Red||saliva||7.4||Green|
|Dil. Hydrochloric Acid||1||Red||Blood||7.4||Green|
|Gastric Juices||1.4||Red||Eggs||7.8||Greenish Blue|
|Lemon Juice||2.5||Red||Toothpaste||8||Greenish Blue|
|Vinegar||4||Orange||Baking Soda Sol.||8.5||Greenish Blue|
|Tomato juice||4.1||Orange||Washing Soda Sol.||9||Blue|
|Coffee||5||Orange Yellow||Milk of magnesia||10.5||Navy Blue|
|Soft drinks||6||Greenish yellow||Household ammonia||11.6||Purple|
|Milk||6.5||Greenish Yellow||Dil. Sodium Hydroxide||13||Violet|
|Pure Milk||7||Green||Conc. Sodium Hydroxide||14||Violet|
Importance Of pH In Everyday Life:
- pH in our digestive system: Our stomach produce Dil. Hydrochloric Acid which helps in digesting our food without harming the stomach. When our stomach produce excess acid it causes indigestion and lower the pH of our stomach which cause pain and irritation. In order to cure indigestion we take a mild base known as ‘Antacid‘ which neutralize the acid in our stomach and bring its pH back to 5.
- pH change as the cause of tooth decay: After eating something the bacteria present in our mouth breaks down the sugar to form acids causing lowering the pH of mouth. Tooth decay starts when the pH of mouth falls below 5.5, at this point the acid become strong enough to to attack tooth enamel and corrode it. The best way to prevent tooth decay is to clean the mouth after eating and using a basic toothpaste which can neutralize mouths acid.
- Self Defense by animals and plants through chemical warfare: Many animals and plants protect themselves from their enemies by injecting painful acid or base into their skin. e.g. a honey bee inject an acidic liquid to the person’s body when it stings causing pain an irritation. Baking soda is used as a remedy because being a base it neutralize the injected acid and bring back the pH of human body to 7.4 again.
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