Acids, Bases and Salts-I

Acids, Bases and Salts

Acids and Bases – I

Acids: Acids are those chemical substances which have a sour taste. According to Arrhenius concept, “are substances that release H⁺ ions in an aqueous solution”.

Physical Properties of Acids

              1)      Acids have sour taste.

              2)      Acids acts as electrolytes (i.e. they conduct electricity in aqueous solution).

              3)      Acids are soluble in water.

              4)      Acids are corrosive in nature.

Classification of Acids

              1)      On the basis of source

                   i.     Inorganic acids – They are prepared from the minerals present in the earth’crust and are also called mineral acids. Example- HCl, HNO3

          ii. Organic acids- They are produced by plants and animals. Example, citric acid (lemon), maleic acid (apple), oxalic acid (tomato).

        2)      On the Basis of Ionisation

                                i.            Strong acids – The acids which ionize completely in an aqueous solution like 

                            inorganic acids.

                              ii.           Weak acids – The acids which ionise partially or to a lesser extent in an aqueous 

                           solution like organic acids.

             3)      On the basis of the concentration of acid present in aqueous solution

                            i.      Dilute acid – If the concentration of an acid is low in an aqueous solution, it is called as dilute acid.

                           ii.    Concentrated acid – if the concentration of an acid is high, it is called concentrated acid.

Bases: Bases are those chemical substances which have a bitter taste. According to Arrhenius concept, “are substances that release OH^- ions in an aqueous solution”.

Physical Properties of Bases

           1)      Bases have bitter taste,

           2)      Bases feel soapy to touch.

           3)      Bases act as an electrolyte in aqueous solution.

Classification of bases

          1)      On the basis of ionisation

                                i.            Strong bases- The bases which ionise completely are called strong bases. 
                            For example, KOH, NaOH.

                              ii.           Weak bases- The bases which ionise partially are called weak bases. 
                            For example,   Ca(OH)_{2 ,} Mg(OH)_2.

Alkali – Base that dissolves in water is called an alkali. All alkalies are bases, but all bases are not alkalies.

Indicators – Substances that changes their colour on adding them into an acid or a basic solution.

                                          i.        Natural indicators – These indicators are found in nature. For example, litmus solution is  a purple colour dye obtained from the lichen plant.

Indicator	Colour in acidic medium	Colour in basic medium
Litmus	Red	Blue
Red cabbage extract	Red	Green
Turmeric	Yellow	Reddish
Flowers of Hydrangea plant	Blue	Pink

                                          ii.            Synthetic indicators – The indicators which are synthesised in the lab.

Indicator	Colour in acidic medium	Colour in basic medium
Phenolphthalein	Colourless	Pink
Methyl orange	Red	Yellow

                                       iii.            Olfactory indicators – Those substances whose odour changes in acidic or basic 

                                 medium.

Olfactory indicator	Acid medium	Basic medium
Onion	Characteristics smell	No smell
Vanilla Essence	Retains smell	No smell
Clove oil	Retains smell	Loses smell

Prepared by Ms. Priti Maan