Question

Which of the following metals form ionic carbide when heated with carbon?
  (A) Na
  (B) K
  (C) Li
  (D) Cs

Answer 1

Hint: In chemistry the term carbide is normally used to describe a compound which is composed of a metal and carbon. They are generally classified by the type of chemical bonds present in between them such as ionic or salt like carbides, covalent carbides, interstitial carbides etc.

Complete step by step solution:
- Let’s start with the concept of carbides. They are the compounds which are composed of a metal and carbon atom. There are several types of carbides such as ionic or salt like carbides, covalent carbides, interstitial carbide and intermediate transition metal carbide.
- The ionic carbide or the salt like carbides consists of highly electropositive elements like alkaline earth metals, alkali metal, and also group three elements. The covalent carbides are usually found in carbides of boron and silicon. The cause why these two elements form covalent carbides is due to their comparable electronegativity and size to carbon and because of this, their association is completely covalent in character.
- We are asked to find the metal which forms an ionic carbide when heated with carbon. The metal is lithium. The lithium carbide which has the molecular formula $L{{i}_{2}}{{C}_{2}}$ is also known as dilithium acetylide and is a chemical compound composed of lithium and carbon, an acetylide. $L{{i}_{2}}{{C}_{2}}$ is an intermediate compound which is produced during radiocarbon dating procedures.
- The formation of lithium carbide from lithium and carbon can be represented as follows
\[2Li+2C\to L{{i}_{2}}{{C}_{2}}\]

Therefore the answer is option (C) Li

Note: Keep in mind that the ionic carbides have discrete carbon anions which are of the form ${{C}^{4-}}$. They are sometimes also called as methanides, because they can be viewed as being derived from methane molecules. Also, the carbides are used as abrasive substances, heating elements etc. in the industry.