# Acids And Bases: General Properties

Acids are chemical substances which are characterized by a sour taste in aqueous medium. They have the tendency to turn blue litmus red.On the other hand, bases are chemical substances which are characterized by bitter taste and are slippery to the touch.Some of the bases are soluble in water while others are not. Water soluble bases are known as alkalis. They have the tendency to turn red litmus blue. Acids and bases react with a wide range of chemical compounds to form salts. Some of the chemical reactions of acids and bases are:

Reactions of acids and bases with metals: When a metal reacts with an acid, it generally displaces hydrogen from the acids. This leads to the evolution of hydrogen gas. The metals combine with remaining part of acids to form salt. For example: reaction of sulphuric acid with zinc.

$H_2SO_4 ~+~ Zn ~\rightarrow ~ZnSO4 ~+ ~H_2$

Alkalis (bases that are soluble in water) react with metal to produce salt and hydrogen gas. For example: reaction of zinc with sodium hydroxide.

$2~ NaOH~ +~ Zn ~\rightarrow~ Na_2ZnO_2 ~+~ H_2$

Reaction of metal carbonates/ metal bicarbonates with acids: Metal carbonates/metal bicarbonates react with acids to produce salt, carbon dioxide and water. For example: reaction of sodium carbonate/sodium bicarbonate with hydrochloric acid.

$Na_2CO_3~ + ~HCl~ (aq)~\rightarrow ~2NaCl ~(aq)~ +~ H_2O (l)~ +~ CO_2$

Reaction of metal oxide with acids: Metal oxides react with acids to produce salt and water. For example: reaction of copper oxide and dilute hydrochloric acid.

$CuO~ + ~2HCl ~\rightarrow~ CuCl_2 ~+~ H_2$

Reaction of non-metal oxide with bases: Non-metal oxides react with bases to produce salt and water. For example: reaction of carbon dioxide and lime water (calcium hydroxide)

$CO_2 ~+ ~Ca~ (OH)_2~ \rightarrow~ CaCO_3 ~+ ~H_2O$

Reaction between acids and bases: Acids react with bases to produce salt and water. The reaction between acids and bases to give salts is known as neutralization reactions. For example: reaction of sodium hydroxide with hydrochloric acid.

$NaOH ~+ ~HCl ~\rightarrow~ NaCl ~+ ~H_2O$

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#### Practise This Question

What is the colour change observed in dil. HCl solution when phenolphthalein is added to it?