What are the general properties of carbides?

What are the general properties of carbides?


1 Answers

askIITIians Expert
21 Points
14 years ago

General Properties of carbides are as follows:

(i)    Alkali metal carbides are usually soft and transparent when pure, and are easily decomposed by water or acids with the formation of aliphatic hydrocarbonds. They are non-conductors of electric current in the solid state.

(ii)    Coinage metal carbides are coloured e.g. Cu2C2 (dark brown), Ag2C2 (white) and Au2C2 (yellow) and all are explosive powders.

(iii)    Alkaline earth metal carbides are decomposed by dilute acids or water to yield acetylene gas. They combine with nitrogen when heated in it.

        CaC2 + 2H2O → Ca(OH)2 + C2H2
        CaC2 + N2 →CaCN2 + C

They reduce magnesium oxide to magnesium.

        3MgO + CaC →3Mg + CaO + 2CO

They react with ammonia and bromine as:

        CaC2 + 4NH3  → CaCN2 + NH4CN + 4H2
        CaC2 + 4Br2  → CaBr2 + C2Br6

Beryllium carbide is a brick red coloured compound, hard enough to scratch glass and quartz.

(iv)    Aluminium carbide is pale yellow hard crystalline substance m.p. 2200oC and is decomposed by water liberating methane. It reacts with nitrogen at 1800oC to form AI5C3N and with oxygen to form alumina.

        AI4C3 + 6O2  → 2AI2O3 + 3CO2

(B)    Covalent Carbides : Hydrocarbons (CH4, C2H6, C6H6 …….) and other compounds such as CS2, CCI4 etc. are also called carbides. But true covalent carbides are those of boron, B4C silicon, SiC.

(C)    Metallic or Interstitial Carbides : The carbides of the metals of group IVB, VB and VIB of the periodic table constitute a related group of compound remarkable for their refractory nature and true metallic properties. They are known as interstitial carbides.

The interstitial carbides are formed by transition metals which have atomic radii large enough to permit the accommodation of carbon atoms in the octahedral holes of the close packed metallic lattice. They have sodium chloride type structure.

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