Acids, Bases and SaltsSCIENCE AND TECHNOLOGY176NotesMODULE - 2Matter in our Surroundings(b) Acid RainWhen the pH of rain water falls below 5.6, it is called acid rain. When acid rainflows into rivers, the pH of the river water also falls and it become acidic. As a result,the survival of aquatic life become difficult.(c) pH in plantsPlants have a healthy growth only when the soil has a specific pH range which shouldbe neither highly alkaline nor highly acidic.(d) In digestive systemOur stomach produce hydrochloric acid which helps in digestion of food. Whenwe eat spicy food, stomach produces too much of acid which causes ‘acidity’ i.e.irritation and sometimes pain too. To get rid of this we use ‘antacids’ which are baseslike ‘milk of magnesia’ (suspension of magnesium hydroxide in water).(e) Self defence of animals and plantsBee sting causes severe pain and burning sensation.It is due to the presence of methanoic acid in it. Useof a mild base like baking soda can provides relieffrom pain.Some plants like ‘nettle plant’ have fine stinging hairwhich inject methanoic acid into the body of anyanimal or human being that comes in its contact. Thiscauses severe pain and buring sensation. The leavesof dock plant that grows near the nettle plant whenrubbed on the affected area provides relief.