Some important hydrocarbons and their compounds

Methane, ethane, propane and butane are among the simplest compounds made of carbon and hydrogen alone. A compound of just these two elements is called a hydrocarbon. In all four of these compounds, the carbon atoms are joined to each other by single covalent bonds only. Every other bond a carbon atom can make is taken up by a hydrogen atom, so there is no room left to add anything more. A hydrocarbon of this kind is called a saturated hydrocarbon, and these four belong to the family called alkanes.

The name of each gas tells you how many carbon atoms it has. The first part of the name counts the carbon atoms, and the ending "ane" tells you that the carbon atoms are joined by single bonds only.

• meth + ane = methane: 1 carbon atom
• eth + ane = ethane: 2 carbon atoms
• prop + ane = propane: 3 carbon atoms
• but + ane = butane: 4 carbon atoms

These four gases share several properties. All four are gases at room temperature. They have no colour and no smell. They do not dissolve in water, but they do dissolve in organic solvents such as ether and alcohol. All four give out heat when they burn, which makes them useful as fuels. Where they differ is in where each one is found and in what each one is used to make, so each is described separately below.

Methane is the simplest hydrocarbon. Its molecular formula is \( \mathrm{CH_4} \). Its molecule has one carbon atom in the middle, with four hydrogen atoms joined to it, each by a single bond.

When leaves and plants rot under water in marshy places, methane is formed and rises to the surface as bubbles. This is why methane is also known as marsh gas. Methane is also generally found underground, collected above deposits of mineral oil (petroleum). It is found in gobar gas, also called biogas, which is made when cattle dung rots in a closed tank, and in the gases given off by sewage.

Methane is colourless, odourless and tasteless. It does not dissolve in water, but it dissolves in organic solvents such as ether and alcohol. Because it does not dissolve in water, it escapes from marsh water as bubbles instead of staying in it.

• Methane is used for cooking food, as gobar gas or biogas, and as a fuel in industries.
• It is used to prepare carbon black, which is used to make printing ink, shoe polish and paint.
• It is used to prepare chloroform, carbon tetrachloride, methyl alcohol, formaldehyde and similar compounds.
• It is used in the industrial preparation of hydrogen gas.

The flame of a biogas stove in a village home comes from methane. Methane gives a lot of heat when it burns and produces little smoke. When methane burns with too little air, it leaves behind a fine black powder of carbon. This powder is carbon black, and it is what makes printing ink, shoe polish and black paint dark.

Ethane is also a saturated hydrocarbon. It has two carbon atoms joined by a single covalent bond, and each carbon carries three hydrogen atoms. Its molecular formula is \( \mathrm{C_2H_6} \).

Ethane is found mixed with methane in natural gas, in coal gas and in petroleum mines. Like methane, it is colourless, odourless and tasteless. It is insoluble in water but soluble in organic solvents such as ether and alcohol.

• Ethane produces heat when it burns, so it is used in metal welding.
• It is used to prepare carbon compounds such as ethyl chloride and nitroethane.

Welding joins two pieces of metal by heating their edges until they melt together. This needs a very hot flame, and the heat given out by burning ethane can supply it.

Propane is also a saturated hydrocarbon. Its molecule has three carbon atoms joined in a row by single bonds, with eight hydrogen atoms in all. Its molecular formula is \( \mathrm{C_3H_8} \).

Propane is also found in natural gas and in petroleum mines. It is a colourless and odourless gas. It is insoluble in water but soluble in organic solvents.

• Propane catches fire very easily, so it is used as a fuel.
• It is used to make different kinds of carbon compounds.
• It is used as a coolant in petroleum industries.

Butane is also a saturated hydrocarbon. Its molecule has four carbon atoms joined in a row by single bonds, with ten hydrogen atoms in all. Its molecular formula is \( \mathrm{C_4H_{10}} \).

Butane is also found in natural gas and in petroleum mines. It is a colourless and odourless gas. It is insoluble in water but soluble in organic solvents.

• It is used as a raw material for making synthetic rubber.
• It is mixed with methane in LPG (Liquefied Petroleum Gas), which is used as a fuel.

Butane changes into a liquid easily when pressure is applied. Because of this, a large amount of gas can be squeezed into a small cylinder as a liquid. This is the gas in the cooking cylinders used at home. When the regulator is opened, the pressure drops and the liquid turns back into gas that flows to the stove.