Short Notes: pH (Acid, Bases and Salts)

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:

  1. Neutral substance has the pH of exactly 7.  e.g. Pure water is neutral in nature it has the pH  7.
  2. Acidic substance has the pH less then 7 because the pH value will decrease with the increase in the conc. of hydrogen ion
  3. 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

pH Color Strength   pH Color Strength
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
7 Green Neutral

Some common substance, their pH value and their corresponding colors

Solutions pH Color Solutions pH Color
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:

  1. 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.
  2. 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.
    Image result for pH change and tooth decay
           Fig. 3: Tooth Decay
  3. 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.
Image result for bee sting
   Fig. 4: Bee Sting

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