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Acids, Bases and Salts

Introduction

     Acids and bases can be better distinguished with the help of indicators. Indicators are substances that undergo a change of colour with a change of acidic, neutral or basic medium.

Understanding the Chemical Properties of Acids and Bases

     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.

Acids and Bases

     A base is a substance, which on dissolving in water yields hydroxyl ions (OH-) as the only negative ions.

How Strong are Acid or Base Solutions?

     An acid, which dissociates completely or almost completely in water, is classified as a strong acid.

More about Salts

     Generally, salts are obtained by treating an acid with a base. Salts consist of both positive ions or 'cations', and negative ions or 'anions'. The cations are called basic radicals and are mostly obtained from metallic ions.

pH of Salts

     Basic salts are stronger in their basic nature and show a pH greater than 7.

Sodium Chloride

     Sodium chloride is the commonly available salt and so is called common salt. Seawater is the main source of sodium chloride. Seawater contains about 3.5% of soluble salts, the most common of which is sodium chloride.

Sodium Carbonate

     Sodium carbonate exists as anhydrous (Na2CO3) and also as hydrated salt. The decahydrated salt (Na2CO3.10H2O) is known as washing soda while the anhydrous salt is called soda ash.

Sodium Hydrogen Carbonate

     Sodium hydrogen carbonate is also known as sodium bicarbonate or baking soda because it decomposes on heating to generate bubbles of carbon dioxide.

Sodium Hydroxide

     Sodium hydroxide is commonly called caustic soda because of its corrosive action on animal and vegetable tissues. Large quantity of sodium hydroxide is prepared by electrolytic process called the 'Chlor-alkali process'.

Water of Crystallization

     When crystals of certain salts are formed, they do so with a definite number of molecules of water, chemically combined in a definite proportion. Water of crystallization is the number of water molecules, chemically combined in a definite molecular proportion, with the salt in its crystalline state.

Plaster of Paris

     Calcium sulphate with half a molecule of water per molecule of the salt (hemi-hydrate) is called plaster of paris (plaster of paris).

Anhydrous Salts

     Certain substances like sodium chloride do not require the help of water to form their crystalline shape.

Effect of Heat on Hydrous Salt

     On heating, hydrous crystals lose their water of crystallization and turn into a powder. They are then said to be anhydrous. Sometimes they may also lose their colour.

Summary

     Strength of an acid depends on the concentration of hydronium ions present in a solution. Greater the numbers of hydronium ions present, greater is the strength of the acid.


Question and Answers

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Multiple Choice Questions

     



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