Question

Identify the correct order of acidic strength of $C{O_2},\,CuO,\,CaO,\,{H_2}O$ .
(A) $CaO < CuO\, < \,{H_2}O < C{O_2}$
(B) ${H_2}O < CuO\, < \,CaO < C{O_2}$
(C) $CaO < {H_2}O\, < \,CuO < C{O_2}$
(D) ${H_2}O < \,C{O_2} < \,CaO < CuO$

Answer 1

Hint: All the given compounds are oxides of different elements with the oxidation state of oxygen as $ - 2$ . These elements do not belong to the same group also. The tendency of any compound to accept electrons is called acidity of the compound.

Complete step by step answer:
It can be stated that the more electropositive is the central atom the more basic is the oxide and reverse. Here, the electropositive character follows the order
$Ca > Cu > H > C$
Thu, the acidic strength of the given compounds can be written as:
$CaO < CuO\, < \,{H_2}O < C{O_2}$
Hence option ‘A’ is correct.
Additional information: An oxide which reacts with water to give an acid is called acidic oxide and the one which reacts with water to give a base is called basic oxide. The acidic strength of oxides of different elements will depend on the tendency of oxygen atoms to accept electrons. If oxygen is attached to some electropositive element its tendency to gain electrons decreases as the electropositive elements tend to lose electrons and its basic strength increases. When the oxygen atom is attached to some electronegative element its acidic character increases as the electronegative element pulls the electrons towards its side. In the periodic table the electropositive character decreases from right to left across a period and increases down the group. In general, the oxides of metals are basic oxides and those of non-metals are acidic oxides.

Note:
The order of electronegativity of the central atom should not be confused. It’s easy, more electropositive nature, more basic character. More is the electronegative nature more is the acidic character.