Hydrocarbons Archives

Classification of Hydrocarbons

The compounds containing only carbon and hydrogen in their molecules are called hydrocarbons.
Hydrocarbons are classified into two categories known as open chain hydrocarbons and closed chain hydrocarbons. Open chain hydrocarbons are also called aliphatic hydrocarbons or acyclic hydrocarbons.

Open and closed chain hydrocarbons
Let us observe the following structural formulae of different hydrocarbons.
1) CH₃–CH₂–CH₂–CH₂–CH₃ n-pentane, a straight chain compound.

Iso pentane, a branched chain compound

cyclo pentane, a cyclic compound or a ring compound

In the first example you will notice that all carbons are linked to one another resulting a linear structure, where as in the second example four carbons are linked in linear way and the fifth carbon is linked to the parent chain resulting a branch. In the third example we find that carbon chain is closed to form a ring. So, it is a closed chain hydrocarbon or ring hydrocarbon.

All hydrocarbons (both Aliphatic and cyclic hydrocarbons) are again classified as Alkanes, Alkenes and Alkynes:
1) Hydrocarbons containing only single bonds between carbon atoms are called Alkanes.
2) Hydrocarbons containing atleast one double bond between carbon atoms are called Alkenes, and
3) Hydrocarbons containing atleast one triple between carbon atoms are called Alkynes.

Saturated and unsaturated hydrocarbons
The hydrocarbons containing only C–C single bonds are known as saturated hydrocarbons. All alkanes are saturated hydrocarbons. The hydrocarbons that contain at least one double bond (C=C) or contain atleast one triple bond (C ≡ C) between the two carbon atoms are called unsaturated hydrocarbons. Alkenes and Alkynes are the examples for unsaturated hydrocarbons.
Straight chain, branched chain and closed chain hydro carbon compounds may be saturated or unsaturated. See the following examples.
Classification of Hydrocarbons 3

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What are carbon compounds?

Carbon compounds are compounds which contain the element carbon.
These compounds contain carbon and hydrogen only or carbon and hydrogen in combination with a few other elements such as oxygen, sulphur, nitrogen, halogens and phosphorus.

Organic compounds

Carbon compounds can be classified into two groups:
(a) Organic compounds
(b) Inorganic compounds
Chemists define organic compounds as carbon- containing compounds. However, some exceptions to this definition are
(a) oxides of carbon such as carbon monoxide, CO and carbon dioxide, CO₂
(b) carbonates such as calcium carbonate, CaCO₃
(c) hydrogen carbonates such as sodium hydrogen carbonate, NaHCO₃
(d) cyanides such as potassium cyanide, KCN
(e) metallic carbides such as aluminium carbide, Al₄C₃
Inorganic compounds include all non-carbon-containing compounds and the few carbon- containing compounds just mentioned.
Table shows examples of organic and inorganic compounds found in nature.
Most organic compounds contain the elements carbon and hydrogen. Hence, complete combustion of organic compounds produces carbon dioxide and water.
The following equation shows the complete combustion of glucose, C₆H₁₂O₆.

Complete combustion of organic compounds experiment

Aim: To investigate the complete combustion of organic compounds.
Materials: Ice, ethanol, palm oil, limewater, water.
Apparatus: Beaker, boiling tubes, rubber stoppers with two holes, delivery tubes, rubber tubing, filter funnel, filter pump, spirit lamp, Bunsen burner, thermometer, test tube holder, retort stand and clamps, wooden blocks.
Procedure:

A spirit lamp is filled with some ethanol and the apparatus is set up as shown below.
The spirit lamp is lit to let the ethanol burn. At the same time, the filter pump is turned on.
Changes taking place in boiling tubes A and B are noted and recorded.
After about 15 minutes, the filter pump is turned off and boiling tube A is removed.
The liquid inside boiling tube A is heated until it starts to boil. The boiling point of the liquid is recorded.
Steps 1 to 5 are repeated using palm oil to replace ethanol.

Observations:

The colourless liquid in boiling tube A boils at 100°C.
The limewater turns milky.

Discussion:

When an organic compound is burnt in excess oxygen,
(a) the carbon combines with oxygen to form carbon dioxide.
C + O₂(g) → CO₂(g)
(b) the hydrogen combines with oxygen to form water.
4H + O₂(g) → 2H₂O(g)
Carbon dioxide is detected through its ability to form a white precipitate with limewater.
When a liquid boils at 100°C and 1 atmospheric pressure, it is pure water.

Conclusion:
Complete combustion of an organic compound produces carbon dioxide and water.

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Hydrocarbons

Hydrocarbons are the simplest of all organic compounds, containing only carbon and hydrogen.
Hydrocarbons are classified into two groups:
(a) Saturated hydrocarbon
(b) Unsaturated hydrocarbon
Saturated hydrocarbon molecules are made entirely of carbon-carbon single bonds. Saturated hydrocarbons contain only single covalent bonds.
Unsaturated hydrocarbon molecules contain at least one carbon-carbon double or triple bond. Unsaturated hydrocarbons contain multiple bonds.
Example:
The most common natural sources of hydrocarbons are petroleum, coal, natural gas and certain trees such as the rubber tree.
Non-hydrocarbons are organic compounds in which some or all of the hydrogen atoms have been replaced by other atoms such as oxygen, nitrogen, phosphorus or halogens.
For example,

(a) sugar is a compound of carbon, hydrogen and oxygen.
(b) protein contains carbon, hydrogen, oxygen and nitrogen.
(c) tetrachloromethane contains carbon and chlorine.