Question

The ionic carbide is:
(A) ${\text{ZnC}}$
(B) ${\text{TiC}}$
(C) ${\text{SiC}}$
(D) ${\text{Ca}}{{\text{C}}_{\text{2}}}$

Answer 1

The term ‘carbide’ in chemistry is used to describe a compound which is composed of carbon and a metal. Carbides are generally classified by the type of chemical bonds present in them. These are salt-like or ionic carbides, covalent carbides, interstitial carbides and intermediate transition metal carbides.

Complete step by step answer:
The ionic carbides are also known as salt-like carbides or saline carbides. They consist of highly electropositive elements such as the alkali metals, alkaline earth metals and also group 3 elements. Ionic carbides contain discrete carbon anions of the forms ${{\text{C}}^{{\text{4 - }}}}$ called methanides as they are derived from methane, ${{\text{C}}_2}^{{\text{2 - }}}$ called acetylides and derived from acetylene, ${{\text{C}}_3}^{{\text{4 - }}}$ called allylides and derived from allene.
Since calcium is an alkaline earth metal, it forms an ionic carbide containing the acetylide anion ${{\text{C}}_2}^{{\text{2 - }}}$ which is calcium carbide having the formula ${\text{Ca}}{{\text{C}}_{\text{2}}}$ . Therefore, option D is correct.
Only two carbides are considered to be completely covalent and they are formed by the elements which are most similar to carbon in electronegativity and size. These are boron and silicon. Silicon carbide or ${\text{SiC}}$ is thus a covalent carbide. It is also known as carborundum and is prepared by the reduction of silicon dioxide with elemental carbon. Therefore, option C is not correct.
The interstitial or metallic carbides are formed by the elements of group 4, group 5 and group 6 transition metals. They have metallic properties and are also called as interstitial compounds. Titanium is a group 4 element and so its carbide ${\text{TiC}}$ is interstitial and so option B is not correct.
The zinc carbide contains zinc which is not a highly electropositive element. Therefore, it is not an ionic carbide and hence option A is wrong.

Note:
Calcium carbide acts as a source of acetylene in the chemical industry. Acetylene is formed by the reaction of calcium carbide with water.
${\text{Ca}}{{\text{C}}_{\text{2}}}{\text{ + 2}}{{\text{H}}_{\text{2}}}{\text{O}} \to {{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}{\text{ + Ca}}{\left( {{\text{OH}}} \right)_{\text{2}}}$
An important industrial reaction of calcium carbide is its reaction with nitrogen to form calcium cyanamide ${\text{CaC}}{{\text{N}}_{\text{2}}}$ as calcium cyanamide is extensively used as a fertilizer.
${\text{Ca}}{{\text{C}}_{\text{2}}}{\text{ + }}{{\text{N}}_2} \to {\text{CaC}}{{\text{N}}_{\text{2}}}{\text{ + C}}$