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.
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.
A base is a substance, which on dissolving in water yields hydroxyl ions (OH-) as the only negative ions.
An acid, which dissociates completely or almost completely in water, is classified as a strong acid.
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.
Basic salts are stronger in their basic nature and show a pH greater than 7.
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 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 is also known as sodium bicarbonate or baking soda because it decomposes on heating to generate bubbles of carbon dioxide.
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'.
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.
Calcium sulphate with half a molecule of water per molecule of the salt (hemi-hydrate) is called plaster of paris (plaster of paris).
Certain substances like sodium chloride do not require the help of water to form their crystalline shape.
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.
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.