Acids, Bases and Salts - Part I

Introduction
All the elements in nature fall into three classes : metals, non-metals and gases. Non-metals are also sometimes called metalloids. The compounds formed by combination of the elements can also be classified as organic and inorganic compounds. Organic compounds are formed from a combination of carbon and hydrogen; they are also sometimes known as hydrocarbons. (Carbon has a unique place in our lives. Each living cell, food, wood, paper, petro-chemicals, cooking gas, perfumes, etc are all made up of carbon). Inorganic compounds are those that are made up of combination of all other elements that do not fall into the category of hydrocarbons. In addition to this, all these compounds taste either sour, bitter or salty.  The sour tasting substances are known as acids. Bitter tasting compounds are generally soapy to feel also; they are known as bases or alkalis.

What we will study in this chapter :
1. ions and radicals
2. acids and bases
3. pH of a solution
4. neutralization and salts

1. Ions and radicals
Atom is electrically neutral. But if it is stripped of electrons it gets a positive charge. This is because there is an imbalance of positive and negative charges. Similarly if an atom attracts extra electrons, it becomes negatively charged. The charged atoms are called ions. 

      Na                                           Na ⁺                 +                   e^-        
     (neutral sodium atom)                          (positive sodium ion)                     (electron)         

    Cl                +               e^-                                      Cl^- 
     (neutral chlorine atom)            (electron)                           (negative chlorine ion)

Sometimes in a chemical reaction of compounds the constituent elements are not released, but there may be a group of atoms sticking together. These groups are called radicals. Thus a radical is a component of a compound consisting of groups of atoms. Radicals can be positively as well as negatively charged. To simplify the jargons, ions are called simple radicals and groups of atomic radicals are called compound radicals. For example (OH) is called a radical and is negatively charged. Hence it is written as (OH)^-, Other common compound radicals are (SO₄)^--, (NO₃) ^--, etc.

2. Acids and bases
In a solution, if  a chemical compounds leads to excess H⁺ions, the solution is termed as an acid solution. Table below lists some of the common acids available in our everyday lives.

All acids taste sour and are mostly derived from oxides of non-metals dissolved in water.  *

On the other hand, if there are excess of (OH)^- ions when a compound is dissolved in water, the solution is called a base or an alkaline solution. A base is generally a metal hydroxide solution. Table below lists some of the common alkalis available in our everyday lives.

(OH)^- is called the hydroxyl radical. All alkalis feel soapy and taste bitter. Some oxides of metals may not be soluble in water, but display all characteristics of bases. They are not called as alkalis. CuO, MgO are some of the metal oxides which fall in the category of bases.

Acids and alkalis have one very distinguishable property. They change colour of certain chemicals, when they are brought in contact. In an acidic medium a litmus paper turns red; in an alkaline medium a litmus paper turns blue. Thus litmus paper is known as an indicator. 

Thus an indicator is a chemical that shows by means of sharp change in color the acidity/alkalinity of a solution. Many other indicators change color when the acidity/alkalinity of the medium fluctuates. One such is phenolphthalein. It is deep pink in an alkaline medium and the pinkness reduces as the alkalinity reduces. It is colorless in an acidic medium.



*Never Taste An Acid - They Are Potentially Harmful.

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