Question

What happens when metallic aluminum reacts with concentrated solution of potassium hydroxide?
(a) $K Al{{(OH)}_{4}}$formed
(b) $Al{{(OH)}_{3}}$formed
(c) $A{{l}_{2}}{{O}_{3}}$formed
(d) None of these

Answer 1

Hint: When aluminum is made to react with the concentrated potassium hydroxide , it undergoes redox reactions with aluminum undergoing oxidation and change in oxidation state is from 0 to +3 and hydrogen undergoing reduction with change in oxidation state from +1 to 0. Now solve it.

Complete step by step solution:
- Aluminum is a metal having atomic number as 13 and mass number as 26 and belongs to the boron family and comes under the category of the p-block elements. On the other hand, potassium hydroxide is a strong base having pH more than seven and turns red litmus blue.
- When metallic aluminum is reacted with the concentrated solution of potassium hydroxide , it undergoes redox reaction ( i.e. those chemical reactions in which the reactants undergo change in their oxidation states by either losing the electrons or by the gain of electrons). The resultant of the redox reaction is the formation of the potassium aluminum hydroxide and there is the evolution of hydrogen gas along with it. The reaction occurs as;
\[2Al+2KOH+6{{H}_{2}}O\to 2KAl{{(OH)}_{4}}+3{{H}_{2}}\]
- In this reaction, aluminum metal undergoes oxidation and its oxidation state increase from 0 to +3 in the potassium aluminate i.e.$ K Al{{(OH)}_{4}}$ and the hydrogen in potassium hydroxide undergoes reduction and its oxidation state decreases from +1 to 0 in the hydrogen gas.

So, the correct answer is option (a).

Note: Potassium aluminate i.e.$ K Al{{(OH)}_{4}}$ formed is an inorganic substance and when this reacts with sulphuric acid , it results in the formation of potassium alum which is used for antiseptic purposes. The reaction occurs as;
\[K Al{{O}_{2}}++2{{H}_{2}}S{{O}_{4}}\to K Al{{(S{{O}_{4}})}_{2}}+2{{H}_{2}}O\]