Types of Hydrocarbons and Laboratory Cracking
This page delves deeper into the different types of hydrocarbons and provides a practical example of cracking in a laboratory setting.
Alkenes, such as propene, are a family of hydrocarbons similar to alkanes but with a distinctive double bond. The structural formula of propene is presented, highlighting its unsaturated nature.
Example: Propene (C₃H₆) structural formula:
H₂C=CH-CH₃
In contrast, alkanes like octane have only single bonds between carbon atoms and are considered saturated hydrocarbons.
Highlight: The presence of a double bond in alkenes makes them unsaturated, while alkanes with only single bonds are saturated.
The page then describes a laboratory setup for cracking liquid paraffin, a practical demonstration of the cracking process:
- Liquid paraffin is heated strongly in a porous pot.
- The resulting gases are passed through a delivery tube.
- One of the products, ethene, is collected and tested.
Vocabulary: Catalytic cracking involves the use of a catalyst to facilitate the breaking down of hydrocarbons, while thermal cracking relies solely on high temperatures.
The test for ethene involves its reaction with bromine water. When ethene is bubbled through bromine water, it causes the brown/orange color to become colorless. This reaction occurs because the double bond in ethene breaks and bonds with the bromine atoms.
Definition: The decolorization of bromine water by ethene is a characteristic test for unsaturated hydrocarbons, demonstrating the presence of a carbon-carbon double bond.
This practical experiment illustrates the conditions needed for cracking and provides a tangible example of how larger hydrocarbons can be broken down into smaller, more reactive molecules through the application of heat.
