Chapter – 2 ACID, BASE AND SALT

In the previous chapter, we talked about chemical reactions. Here, we will discuss acid, base and their neutralization reaction that leads to the creation of salt.

2.1 What is acid?

Acid is a compound that breaks up in water to give of Hydronium (H+) ions.  That is, it has the potential of releasing hydrogen ion.

2.1.1. Characteristics of acid

Listed below are some of the characteristic that can help you identify acid. Have a look at them.

  • pH < 7
  • It contains replaceable H atom.
  • The taste is sour.
  • Acid turns blue litmus paper red and Methyl Orange colorless.
  • It liberates hydrogen gas when reacted with metal.
  • It liberates carbon dioxide gas when reacted with carbohydrate.
  • It liberates nitric oxide gas when reacted with nitrate. (Nitric oxide is recognized by brown fumes)
  • It liberates sulphur dioxide gas when reacted with sulphites.
  • It liberates hydrogen sulphide gas (pungent smell) when reacted with sulphides.

2.2 What is a base?

Unlike acid, base accepts hydrogen ion instead of releasing it. They neutralize acid to create salt. Bases are classified into the strong and weak base.

A base that completely ionizes water and releases a large amount of hydroxide ion is called strong base. The hydroxides of active metals like sodium, potassium, lithium, and others are considered as a strong base.

A base that partially ionizes water and releases a small amount of hydroxide ion is called weak base. The hydroxides of metals like aluminum, calcium, and others are considered as a weak base.

Listed below are some of the characteristics of a base.

  • pH > 7
  • Bases are a good conductor of electricity.
  • It is a compound of metal and has replaceable OH
  • It tastes bitter and is soapy in touch.
  • Turns red litmus paper blue
  • Oil and sulphur dissolves in bases.
  • Water soluble bases include metal hydroxides namely NaOH, KOH, Ca(OH)2
  • Water insoluble base includes metal oxides namely CuO, BaO, Fe(OH)

2.4 How do acid reacts with metals?

The various reaction of the acid with metal and its compounds are listed below.

2.4.1 Metal

Metal + Acid = Salt + Hydrogen gas

For Example :               H2SO4 + 2Ca = Ca2SO4 + H2

                                                                HNO3 + 2Na = Na2NO3 + H2

2.4.2 Metal Carbonate

Metal Carbonate/ Metal Hydrogen carbonate + Acid = Salt + Carbon Dioxide + Water

For Example :               CaCO3 + 2HCl = CaCl2 + CO2 + H2O

Ca(HCO3)2 + 2HCl = CaCl2 + 2CO2 + 2H2O

 

2.4.3 Metal Oxide

Metal Oxide + Acid = Salt + Water

For Example :               CaO + 2HCl = CaCl2 + H2O

K2O + H2SO4 = K2SO4 + H2O

2.4.4 Water

When dissolved in water acid produces H+ ion. However, hydrogen ion cannot exist alone, so, it exists in the combination of water, i.e., in the form of hydronium ion (H3O+).

The chemical reaction of the same is mentioned below.

HCl + H2O = H3O+ + Cl

The hydronium ion is a combination of water of hydrogen ion (H+).

H+ + H2O     =        H3O+

2.5 Reaction of Base with non-metallic elements and its compounds

Mentioned below are some of the reactions of a base with a non-metallic element and its compounds.

2.5.1 Reaction with water

Base dissociates in water to form hydroxide ion.

For example: Consider B is a base. So, following chemical reaction takes place with water.

B + H2O = BH+ + OH

Similarly,             KOH + H2O = K+(aq) + OH(aq)

 

2.5.2 Non-metallic Oxide

Non-metallic Oxide + Base = Salt + Water

For example :               Ca(OH)2 + CO2 = CaCO3 + H2O

2.5.3 Neutralization Reaction

Base reacts with acid to neutralize and vice-versa. The neutralization reaction produces salt and water.

Base + Acid = Salt + Water

For example :               2NaOH + H2SO4 = Na2SO4 + 2H2O

K2O + 2HCl = 2KCl + H2O

 

 2.6 Strength of Acid and Base

The scale for measuring the concentration of hydrogen is known as the pH scale. The strength of acids and bases is measured on the scale of 14. The pH value of the most acidic solution is 0 while that of the strongest alkaline is 17. The solution with pH 7 is said to be neutral. The pH value of pure water and blood is said to be 7.

 

2.7 Salt

Salts of a strong acid and strong base are 7. While when a strong acid is reacted with a weak base, then, the pH of the salt shifts from 7 to 0. Similarly, when a weak acid is reacted with a strong base, then, the pH of the salt shifts from 7 to 14.

Common Salt

The common salt sodium chloride (known as brine) used in every household is the combination of hydrochloric acid and sodium hydroxide.

The various reactions of the common salt are listed below.

2.7.1 Sodium Hydroxide

The aqueous solution of the sodium chloride, when reacted with water, produces sodium hydroxide and hydrogen and chlorine gas.

2NaCl + 2H2O = 2NaOH + H2 + Cl2

2.7.2 Baking Soda (NaHCO3)

NaCl + H2O + CO2 + NH3 = NH4Cl + NaHCO3

 

Uses of baking soda

  • Baking soda is used in used in baking cakes. The reaction with mild acid in presence of heat, it produces Carbon Dioxide that makes the bread soft and spongy                          H+ + NaHCO3 = Na2CO3 + H2O + CO2
  • It is used in antacid, in order to, reduce acidity in the stomach.
  • It is even used in soda-acid fire extinguisher.

2.7.3 Bleaching Powder (CaOCl2)

Ca(OH)2 + Cl2 = CaOCl2 + H2O

Uses of bleaching powder

  • It is used in an oxidizing agent
  • It is used for disinfecting drinking water
  • It is also used for washing clothes.

 

 

 

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