Saturated Hydrocarbons – Alkanes
The alkanes are aliphatic hydrocarbons. They form a homologous series of saturated hydrocarbons which can be represented by the general molecular formula CnH2n+2. In each alkane number, all the carbon atoms are tetrahedrally bonded to the hydrogen and other carbon atoms. These hydrocarbons contain only C-C single bonds in their molecules are called alkanes. These include open chain as well as closed chain (cyclic) hydrocarbons. For example, ethane, propane cyclopentane.
Alkanes are further divided into:
- Open chain or acyclic (simple alkanes not having any closed chains). They have the general formula CnH2n+2. Examples are methane (CH4), propane (C3H8) and butane (C4H10).
- Cycloalkanes or cyclic alkanes (having a closed chain or rings in their molecules). They have the general formula CnH2n. Examples are cyclopropane (C3H6) and cyclobutane (C4H8)
The simplest Hydrocarbon is methane, CH4. This is the simplest member of a series of hydrocarbons. Each successive member of the series has one more Carbon atom than the preceding member. This is shown in the table below.
Methane
The simplest compound in the alkane series with the molecular formula of CH4. Besides being a component of petroleum gas, it is the major constituent of natural gas. Methane is produced during the decomposition of plant matter in the absence of air.
Laboratory Preparation
Methane is usually prepared by heating anhydrous sodium ethanoate with an alkali, usually soda lime (quick lime slaked with a concentrated solution of NaOH). Anhydrous sodium ethanoate is ground with an equal mass of soda lime and then heated in a hard glass test tube. Methane is given off and can be collected over water.
CH3COONa(s) + NaOH(s) →Na2CO3(s) + CH4(g)…
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