|
As acids and bases are highly corrosive and reactive substances it is important to understand their reaction and responses on substances commonly found around us. It helps us to understand the outcomes of using them in daily life. Let see the different acids and bases.
Some common acids that are found in laboratories are Hydrochloric acid (HCl), Sulphuric acid (H2SO4) and Nitric acid (HNO3). Some of the lesser used acids are Acetic acid (CH3COOH), Hydrofluoric acid (HF), Carbonic acid (H2CO3). Hydrofluoric acid is a highly corrosive acid and is used to etch glass. Some acids are found in nature, like citric acid in certain fruits. These acids are called 'organic acids'. Examples are:
- Citric acid (from citrus fruits and vegetables,)
- Ascorbic acid (vitamin C, as from certain fruits)
- Acetic acid (Vinegar)
- Lactic acid (in buttermilk)
- Tartaric acid (Tamarind)
- Oxalic acid (Tomatoes)
Commonly found bases in laboratories and in our daily life are: Caustic soda, NaOH; Caustic potash, KOH; Milk of magnesia, Mg(OH)2; Liquor ammonia, NH3; Washing powder, Tooth paste.
One can familiarize with the acid base nature of some of the common substances by using litmus solution.
Make solutions of the following substances:
'Borax', 'Blood', 'Milk', 'caustic soda', 'Lemon Juice', 'Bleaching powder', 'Tomatoes', 'Vinegar', 'detergent', 'Pure Water', 'Coffee', Baking Soda'.
Put a drop of each of the above solutions on a watch-glass and test by adding a drop of litmus to it.
Suggested answer:
Lemon juice, vinegar, tomatoes, coffee and milk turn litmus colour red indicating the acidic nature of these substances.
Pure Water does not show any change in colour of the litmus indicating its neutral character.
Blood, baking soda, borax, detergent, household ammonia, bleaching powder, caustic soda turn litmus colour blue showing the basic nature of these substances.
Let us do more activities to understand the chemical nature of acids and bases.
Action on Metals
Let us look at the way acids react with metals.
a) All metals above hydrogen in the metal reactivity series generally react with dilute acids to form their respective salt and liberate hydrogen.
Metal + Acid  Salt + Hydrogen
b) Very active metals like potassium, sodium and calcium also react similarly, but tend to explode when combining with acids.
c) Nitric acid (of various concentrations) usually exhibits oxidizing property, rather than acidic properties. Metals such as magnesium combine with extremely dilute (1%) nitric acid to liberate hydrogen.
Acids react with carbonates and hydrogen carbonates (bicarbonates) to form their respective salt, water and carbon dioxide.
Carbonate/Bicarbonate + Acid  Salt + Water + Carbon dioxide
Acids and bases are the chemical 'opposites' of each other and the action of an acid and a base nullifies the effect of one on the other. This is known as a neutralization reaction.
Neutralization
In a neutralization reaction an acid combines with a base, neutralizing the power of acid with a base and forms a molecule of water and the respective salt.
In general, a neutralization reaction can be written as:
Base + Acid ® Salt + Water
Examples:
Action with Basic Oxides
Oxides that can add on hydroxyl ions (OH-) to their molecules are called basic oxides. These oxides get neutralized when they react with acids.
Basic oxide + Acid  Salt + Water
Action with Basic Hydroxides
Acids undergo neutralization reaction with basic hydroxides to form salt and water.
Basic hydroxide + Acid  Salt + Water
Calcium hydroxide, which is a base, reacts with carbon dioxide to produce a salt and water. Since this is similar to the reaction between a base and an acid, we can conclude that nonmetallic oxides are acidic in nature.
Action of Alkalis/Base with Ammonium Salts
Alkalis combine with ammonium salts to liberate ammonia.
Alkali + Ammonium salt  Salt + Water + Ammonia
| 
