Introduction

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

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

 

ACID	OCCURS IN
acetic acid	vinegar
formic acid	ants sting
citric acid	citrus fruits like lemon, orange
lactic acid	curds
oxalic acid	spinach, tomato
ascorbic acid [vit c]	amla

                         Table 1: Acids and their natural occurrences

 

BASES	OCCUR IN
Calcium hydroxide	lime water
ammonium hydroxide	window cleaner
sodium or potassium hydroxide	soap
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

The acid reacts with the base to get salt and water; heat is always evolved [exothermic]. Salt can be basic, acidic, or neutral. This is called neutralization. Salts of a strong base and strong acid are neutral. Those of strong acid and weak base are acidic and strong base, a weak acid is 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, it’s iron and chromium, nickel, manganese, and carbon

Miscellaneous

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

To remove the 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. Sulfur 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 the 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.