Chemistry (NTSE/Olympiad)  

4. Acid Bases & Salts

Points to Remember

Points to Remember
♦ Everything that tastes sour contains an acid.
♦ Acetic acid, citric acid, tartaric acid are a few organic acids. Sulphuric acid, nitric acid and hydrochloric acid are examples of inorganic acids.
♦ Acids turn blue litmus red, whereas bases turn red litmus blue.
♦ When a solution of an acid contains larger amount of the acid, it is said to be concentrated, while that containing smaller amount of the acid, is said to be dilute.
♦ Metals like sodium, potassium and calcium react with an acid to liberate hydrogen gas.
♦ Acids react with bases to produce salts and water.
♦ Acids react with the carbonates and the hydrogencarbonates to give carbon dioxide gas.
♦ The hydrogen atoms of an acid which can be partially or completely replaced by an atom or a group of atoms are called replaceable hydrogen atoms. They are also called acidic hydrogen.
♦ The number of replaceable hydrogen atoms present in a molecule of the acid is known as the basicity of the acid.
♦ A compound that reacts with an acid to form a salt and water is called a base.
♦ Bases that are soluble in water are called alkalis. All alkalis are bases, but all bases are not alkalis.
♦ The reaction between an acid and a base is called neutralization reaction. In such a reaction, the acid and the base destroy the properties of each other.
♦ The number of hydroxyl groups (OH) present in a molecule of the base is called the acidity of the base.
♦ A salt is a compound formed by the reaction of an acid with a base.
♦ Na2SO4, CaSO4 and Na3PO4 are normal salts, and NaHSO4, NaHCO3, Na2HPO4 are acid salts.
♦ A strong acid is one which gets almost completely dissociated when dissolved in water to give hydrogen ions, whereas a weak acid gets only partially dissociated in water to give hydrogen ions.
♦ A strong base gets almost completely dissociated when dissolved in water to give hydroxide ions (OH–) , whereas a weak base, when treated as such, gets only partially dissociated to provide hydroxide ions.


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