SUMMARY

 

1.    Acids are substances that have the following properties in aqueous solution.

                      i.        They have a sour taste.

                     ii.        Change the colour of litmus, from blue to red.

                    iii.        React with active metals (such as iron, tin and zinc) to liberate hydrogen gas.

                   iv.        React with bases to form salt (ionic compounds) and water.

                    v.        Their aqueous solutions conduct an electric current because they contain ions, they are electrolytes.

2.    Similarly bases are defined as substances that have the following properties, when dissolved in water.

                      i.        They have bitter taste.

                     ii.        Feel soapy and slippery on the skin.

                    iii.        Turn colour of litmus paper from red to blue.

                   iv.        React with acids to form salt and water.

                    v.        They give aqueous solutions which conduct an electricity, they are electrolytes.

3.    Arrhenius proposed that an acid is a substance that yields hydrogen (H+) ions in water solution, while base produces hydroxide (OH) ions.

4.    The Lewis theory defines a base, as any substance that has one or more pair of electrons for bond formation. A Lewis base is an electron-pair donor, while Lewis acid is electron-pair acceptor.

5.    Strong acid is one that ionizes in dilute solution almost completely and weak acid is one that ionizes only slightly. Thus a solution of strong acid has relatively high concentration of (H+) ions and a solution of weak acid has a relatively low concentration of (H+) ions. Similarly strong base is one that ionizes in dilute solution almost completely and weak base is one which ionizes only slightly. Thus a solution of strong base has a relatively high concentration of (OH) ions and a solution of weak base has a relatively low concentration of (OH) ions.

6.    Acids may be classified in terms of number of proton per molecule of acid that can given up in a reaction. Acids HClO4, HI, HBr, HCL, HNO3 and HCN that contain one ionizable hydrogen atom in a molecule of acid are called monoprotic acids. Di-protic acids contain two ionizable hydrogen atoms in one molecule of the acid, ionization of such acids occurs in two steps. Tri-protic acids, such as phosphoric acid, ionizes in three steps. Mono protic, Di-protic and tri-protic acids are commonly called mono basic, dibasic and tribasic. Similarly, bases that produce one (OH) ion per molecule are called mono-acidic bases that produces two (OH) ions per molecule are called di-acidic bases and that produce three (OH) ions per molecule are called tri-acidic bases.

7.    When acids react with bases, salt and water are formed, and is known as neutralization. Many of these reactions can be denoted by a single net-ionic equation.
                                    H+ + OH-
------à  H2O

Salts are formed by any positive ion except hydrogen, combined with any negative ion, except hydroxide ion. Salts are ionic substances which are completely dissociated in water solution and are known as electrolytes.

8.    The acidity of an aqueous solution is expressed by its pH, which is defined as the negative logarthim of the hydrogen ions concentration. (in moles per litre). The neutral solution has pH=7, acidic solution has a pH is less then 7 and basic solution has pH is more then 7 Nowadays pH of a solution is determined by pH-meter.

9.    Most salts are strong electrolytes and dissociates completely in to ions in aqueous solutions. The reaction of these ions, with water lead to the acidic or basic solution, called hydrolysis, the solution of strong acids and weak bases are acidic and the solutions of weak acids and strong bases are basic in nature, but the solutions of strong acids and strong bases are neutral because of the formation of equal concentration of strong acid and strong base.

10. Water is amphoteric because it is both an acid and a base. It undergoes self ionization to give small quantities of hydrogen ion (H+) and hydroxide ion (OH).

11. Standard solution is that whose concentration is known.

12. The concentration of solution is usually expressed as molarity (M), which is defined as the number of moles of solute dissolved per litre of solution. A solution of exact concentration can often be determined by titration. Titration is a chemical process by which we can determine the concentration of unknown (acid) solution by reacting it with a solution of known concentration of (base) solution.

 

 
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