HYDROCARBON PROPERTIES

Hydrocarbons are organic compounds that consist of only C and H atoms. They include the Alkanes, Alkenes, Alkynes and the Aromatic hydrocarbons. These compounds are also refers to as non-polar compounds , because of their nonpolarity, all hydrocarbons are insoluble in water. When these compounds (Hydrocarbons) burns in sufficient oxygen, carbon dioxide and water are the sole product.

These compounds are classified as Saturated or Unsaturated Hydrocarbons this classification only applies to the aliphatic compounds that is the straight or branch chain hydrocarbons depending on the number of bonds in between the carbon atom which is the basis of hydrocarbons structural differences. Thus hydrocarbons can be grouped into families based on their similar properties.

SOURCES OF HYDROCABONS.

Almost all useable supplies of hydrocarbons are obtained from fossil fuels – coal, petroleum, and natural gas. Through distillation crude oil is boiled and condensed over several fractions to give the desired mixture of compounds. Gasoline for example is a fraction boiling roughly between 40 and 200 oC. the vapor that are condensed in this fraction are mostly alkanes and have between 5 to 10 carbon atoms.

Since crude oil and natural gas are the major sources of Hydrocarbon then what is crude oil? Crude oil can be described as a mixture of many compounds, most of them hydrocarbons. Both crude oil and natural gas are mixtures of hydrocarbons; however, crude oil also contains minor amounts of other chemicals, such as sulfur, nitrogen, and oxygen while natural gas is a mixture of simple, small hydrocarbons only.

GENERAL PROPERTIES OF HYDROCARBONS

Hydrocarbons molecules vary a great deal as to how many atoms they contain. A molecule of methane – the main component of natural gas- consists of just one carbon and four hydrogen atoms, while a molecule of polyethylene is along chain of thousands of carbon and hydrogen atoms.

Below are some common simple hydrocarbons, with their molecular structures. Note that the last two have double bonds between their carbon atoms.

Methane H H – C - HCH4 HEthane H H H - C – C - HC2H6 H H Propane

C3H8 Butane

C4H10Propene

C3H6

Hydrocarbons have different boiling points, and can be solids, liquids or gases at room temperature. Small hydrocarbons with only a few carbon atoms have low boiling points and are gases at room temperature, while large hydrocarbons with many carbon atoms have boiling points and are solids at room temperature. e.g waxes and hydrocarbons with between 5 – 12 carbon atoms are usually liquids at room temperature.

TRENDS IN PROPERTIES

The higher the hydrocarbon molecule and more carbon atoms it contains The higher its boiling point. The less easily it turns into vapor i.e it is less volatile. The less easily it flows i.e its more viscous The less easily it ignites i.e it is less flammable.

These trends in properties of hydrocarbon is very important and mostly used in the separation of crude into various fractions, which is achieved by distillation, most widely used is the fractional distillation of crude which differ from the ordinary distillation process that can be used in the separation of pure liquid from a mixture of liquids with different boiling points while fractional distillation on the other hand separates mixtures of liquids for instance crude oil into a number of different parts, called fractions. Hydrocarbons burns in oxygen to produces carbondioxide and water the level of combustion depends on the amount of oxygen involves at this point you need to know what happen when fuels burns, and you may also be expected to know how the gases formed can harm the environment.

The products of combustion differ between complete and incomplete combustion. When hydrocarbons burn they react with oxygen in the air. Burning or combustion is an oxidation process, when they are completely burn the only product is water and carbon dioxide.but when hydrocarbons in a limited supply of air, that is the amount of oxygen is not enough to oxidized all the carbon dioxide. Some of the carbon released aas black soot. Some of it reacts with oxygen to form carbon monoxide, which is a poisonous gas with no smell.

Most fuels naturally contain some sulphur compounds. When the fuel burns, the sulphur reacts with oxygen to form sulphur dioxide. This is gas with a choking smell which dissolves in rain, making it more acidic.

Acid rain can damage rocks, building materials and trees. Plants and animals cannot survive in rivers and lakes that become too acidic from acid rain.

Still on the properties of hydrocarbons lets consider the major families

For example let’s consider some aliphatic hydrocarbons.

Open-chain alkanes (without rings) all have the general formula CnH2n + 2, where n equals the number of carbon atoms. The following table shows the structures and names for the first 10 unbranched, open-chain alkanes. Look at the trends in the boiling and melting points and the density of the alkanes as their mass increases.IUPACname

MolecularFormula

StructuralFormula

BoilingPoint (°C)

MeltingPoint (°C

Density(g/ml, 20°C)

Methane CH4 CH4 -161.5 -182.5Ethane C2H6 C2H6 -88.6 -183.3Propane C3H8

CH3CH2CH3 -42.1 -189.7Butane C4H10

CH3(CH2)2CH3 -0.5 -138.4Pentane C5H12

CH3(CH2)3CH3 36.1 -129.7 0.626Hexane C6H14

CH3(CH2)4CH3 68.7 -95.3 0.659Heptane C7H16

CH3(CH2)5CH3 98.4 -90.6 0.684Octane C8H18

CH3(CH2)6CH3 125.7 -56.8 0.703Nonane C9H20

CH3(CH2)7CH3 150.8 -53.5 0.718Decane C10H22

CH3(CH2)8CH3 174.1 -29.7 0.730

Alkyl Groups

An alkyl is basically an alkane minus one of its hydrogen atoms. For example:

CH4 CH3 - + H+

C2H6 C2H5- + H+

The Significant of the Alkyl group will be explained more latter.

IUPAC System of Naming Alkanes

The IUPAC (International Union of Pure and Applied Chemistry) is composed of chemists representing the national chemical societies of several countries. One committee of the IUPAC, the Commission on Nomenclature of Organic Chemistry, has set a system for naming organic compounds. The last syllable in the name of a compound designates the family to which it belongs. The alkanes all end in -ane. IUPAC Rules for Namining the Alkanes

To be explain further in the class.