Chapter 22: ACID, BASES and SALTS


Acid [pH <7] – Sour, Base [14 > pH > 7] – bitter and soapy to touch. Water soluble base –alkali.

Turmeric, litmus [obtained from lichens], China rose are some natural indicators of acid, base. Vanilla, onions and clove are olfactory indicators.



acetic acid


formic acid

ants sting

citric acid

citrus fruits like lemon, orange

lactic acid


oxalic acid

spinach, tomato

ascorbic acid [vit c]


                         Table 1: Acids and their natural occurances



Calcium hydroxide

lime water

ammonium hydroxide

window cleaner

sodium or potassium hydroxide


magnesium hydroxide

milk of magnesia

                            Table 2: Bases and their natural occurrences

Acid Base tests

Turmeric turns red with soap as soap is basic. Soap is sodium or potassium salt of long chain carboxylic acids, this forms scum with hard water. However detergents are salts of ammonium or sulphonate salts, these don’t form scum with hard water and remain effective. China rose turns dark pink for acidic and green for basic. Phenolphthalein turns colorless with acid and pink with base.

Acid - Base Reactions

Acid reacts with base to get salt and water; heat is always evolved [exothermic]. Salt can be basic, acidic or neutral. This is called neutralization. Salts of strong base and strong acid are neutral. Those of strong acid and weak base are acidic and strong base, weak acid are basic. Blood is basic in nature.

Carbon dioxide turns lime water [calcium hydroxide] into milky [calcium carbonate]

Galvanization is depositing zinc on iron objects to prevent rusting as it cuts off contact of water vapor and oxygen with iron.  Stainless steel doesn’t rust, its iron and chromium, nickel, manganese and carbon


We take milk of magnesia [base] when we get indigestion due to excess hydrochloric acid in stomach.

To remove effect of ant bite [formic acid] we put moist baking soda [sodium bicarbonate] or calamine solution [zinc carbonate]. Nettle sting releases methanoic acid.

By adding excess fertilizers soil becomes acidic so we put quick lime [calcium oxide] or slaked lime [calcium hydroxide] to it. To make it less basic we add organic matter to it.

Acid rain is caused by carbon dioxide, nitrogen dioxide and sulfur dioxide which mix with water to become nitric acid, carbonic acid and sulphuric acid. Sulphur dioxide is emitted by coal based power plants.

Bleaching powder [calcium oxychloride] is used for bleaching clothes and disinfecting water. Washing soda is used for removing permanent hardness of water and as a cleaning agent.

Plaster of Paris or calcium hemihydrates [CaSO4, ½ H2O] is used as a plaster to support fractured bones in the right position. On mixing with water it becomes gypsum [CaSO4, 2H2O] which is hard.


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