Question

In alkaline medium, which elements can produce hydrogen?
 (A)- Zn, Si
(B)- Cu, Ag
(C)-\[\text{Cu, }{{\text{N}}_{2}}\]
(D)- Al, C

Answer 1

Hint: The alkali (that includes the alkali metals and alkaline earth metals) on dissolving in water forms a solution called an alkaline solution. They are basic in nature and donate electrons readily.

Complete step by step answer:
The metals such as zinc, aluminium and metalloid such as silicon are amphoteric in nature as they react with both acid and base to produce hydrogen.

Reaction of zinc:
- Reaction of zinc in an alkaline medium produces sodium zincate and hydrogen.
 \[\text{Zn}\left( s \right)+\text{ 2 NaOH}\left( aq \right)\to \text{N}{{\text{a}}_{2}}\text{Zn}{{\text{O}}_{2}}\left( aq \right)+\text{ }{{\text{H}}_{2}}\left( g \right)\]
- Reaction of zinc in acidic medium produces zinc chloride(salt) and hydrogen gas as zinc is more reactive than hydrogen and displaces it in the reaction according to the reactivity series.
    \[\text{Zn}\left( s \right)+\text{ 2 HCl}\left( aq \right)\to \text{ZnC}{{\text{l}}_{2}}\left( aq \right)+\text{ }{{\text{H}}_{2}}\left( g \right)\]
Reaction of aluminium:
- Reaction of aluminium in an alkaline medium produces aluminate, hydrogen gas and sodium oxide.
\[2\text{ Al}\left( s \right)+\text{ 6 NaOH}\left( aq \right)\to \text{2 NaAl}{{\text{O}}_{2}}\left( aq \right)+\text{ 3 }{{\text{H}}_{2}}\left( g \right)+\text{ }2\text{ Na}{{\text{O}}_{2}}\left( aq \right)\]
- Reaction of aluminium in acidic medium produces aluminium chloride and hydrogen.
\[2\text{ Al}\left( s \right)+\text{ 6 HCl}\left( aq \right)\to \text{2 AlC}{{\text{l}}_{3}}\left( aq \right)+\text{ 3 }{{\text{H}}_{2}}\left( g \right)\]
Reaction of silicon:
- Reaction of silicon (acting as a reducing agent) in alkaline medium produces ortho silicate ang hydrogen.
 \[\text{Si}\left( s \right)+\text{ }4\text{ NaOH}\left( aq \right)\to \text{N}{{\text{a}}_{4}}\text{Si}{{\text{O}}_{4}}\left( aq \right)+\text{ }2\text{ }{{\text{H}}_{2}}\left( g \right)\]
 - Reaction of silicon in acidic medium produces silicon tetrachloride and hydrogen.
  \[\text{Si}\left( s \right)+\text{ 4HCl}\left( aq \right)\to \text{SiC}{{\text{l}}_{4}}\left( aq \right)+\text{ 2}{{\text{H}}_{2}}\left( g \right)\]
Whereas, silver and dinitrogen on reaction with alkaline medium produce water and only in acidic medium produce hydrogen
- \[\text{2 Ag}+2\text{ NaOH}\to \text{ A}{{\text{g}}_{2}}\text{O}+2\text{ Na}+{{\text{H}}_{2}}\text{O}\]
- \[{{\text{N}}_{2}}+4\text{ NaOH}\to \text{ N}{{\text{a}}_{3}}\text{N}+\text{NaN}{{\text{O}}_{2}}+\text{2 }{{\text{H}}_{2}}\text{0}\]
Also, copper itself does not react with an alkaline solution which is more basic and more reactive. Only in concentrated solution, the reaction will proceed.

Therefore, option (A)- Zn, Si are the elements which produce hydrogen in an alkaline medium.


Additional information: The alkaline earth metals constituting Group 2 elements have \[\left( +1 \right)\]nuclear charge greater than the alkali metals due to which size of atom decreases and its first ionization energy increases. This makes the alkaline earth metals less reactive than alkali metals.


Note: The reactivity series of metal allows the displacement of the less reactive metals in the down bottom of the series by the most reactive metals at the top. This is the reason why Hydrogen is being liberated on reaction with Zn and Si.