Key Differences: Saturated vs Unsaturated Hydrocarbons
We are completely aware that an organic compound is made up of carbons and hydrogen atoms. But unsaturated carbons state that adjacent carbon atoms have formed either a double or triple bond with each other. To make them saturated, we need to add more hydrogen atoms to them.
These unsaturated ones can be in the form of straight-chain or branched chains or aromatic compounds. The ones which have at least one double bond between carbon atoms are known as alkenes. But if there is at least one triple bond between carbons in an organic compound, they are alkynes. Below you will understand different types, examples, and the uses of Unsaturated Hydrocarbons in detail.
What are Hydrocarbons? Give Examples.
An organic compound is a hydrocarbon when it contains carbon and hydrogen atoms in it. These can be either saturated or unsaturated. Saturated ones are those having a single bond between two carbon atoms or with a hydrogen atom. Unsaturated ones are those which have either a double or triple bond with two adjacent carbon atoms.
Some basic saturated hydrocarbon examples are methane and ethane. Unsaturated Hydrocarbon examples are Ethene and Ethyne.
What are Different Types of Unsaturated Carbon Compounds?
According to the basic unsaturated hydrocarbon definition, there are three different types. These are:
Alkenes
Alkynes
Aromatic
The classification is based upon the type of carbon-carbon bond in the compound. Also, it is defined by its basic structure.
If there is at least one double bond between two adjacent carbon atoms in a hydrocarbon, those are alkenes or olefins. Ethene is an example of such a type given by \[C_{2}H_{4}\]. These will have only one double bond with no functional groups. The basic formula is given by \[C_{2}H_{2n}\].
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In Alkynes, there is at least one triple bond between two adjacent carbon atoms. An example of such a kind is acetylene given by \[C_{2}H_{2}\]. The basic unsaturated hydrocarbon formula for alkynes is given by \[C_{2}H_{2n - 2}\].
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Aromatic hydrocarbons do not share common properties with other unsaturated carbon compounds. However, listed among these because these are relatively stable.
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If you want to check if a particular hydrocarbon is unsaturated, you can add bromine water to it. In case water turns decolourised, it is unsaturated. If it forms a precipitate, then it is phenol. Also, benzene is the one that will not decolorize bromine water.
What are the Different Uses of Unsaturated Carbon Compounds?
Uses of compounds listed among unsaturated category are:
It is the usual case of ripening fruits with the help of alkenes.
In chemistry, we include unsaturated carbons to synthesize various compounds. They are usually used as monomers in such areas.
Mustard gas is prepared with the help of alkenes which is often required for chemical warfare. It is poisonous.
Acetylene is the fuel used inside a torch that we generally use in a home project.
Unsaturated compounds are generally used in the manufacturing of plastics.
Alkenes are used in industries for synthesizing fuel, detergent, plastic, and alcohol.
The use of Polystyrene is generally for disposable cups, egg cartons, and other convenient products.
Physical Properties of Unsaturated Carbon
As talked about above, unsaturated compounds have either one double or triple bond. These are generally given by the formula \[C_{2}H_{2n}\] and \[C_{2}H_{2n - 2}\].
To make unsaturated as saturated compounds, we need to add hydrogen atoms to them. This will form more carbon and hydrogen bonds.
The carbon-carbon bond formed in a double bond of carbons will form 120 degree angles.
The carbon-carbon bond formed in the triple bond of carbons will form 180 degree angles.
Unsaturated compounds get through different reactions, including combustion reactions, addition reactions, oxidation reactions performed by alkenes, polymerization of alkenes.
Combustion reactions include the formation of carbon dioxide and water.
The addition reaction is either symmetrical or unsymmetrical.
Oxidation Reactions include either addition of oxygen in a molecule or the removal of hydrogen from a molecule.
If reactions are conducted under pressure at a particular temperature with the help of a catalyst, these are polymerization reactions. The molecules produced are polymers.
The most common example of aromatic compounds universally considered is benzene. It forms 120 degrees between constituent carbon atoms.
Saturated Vs Unsaturated Hydrocarbons:
Both the compounds are organic compounds i.e, made up of hydrogen and carbon atoms. The major difference between both is the type of bonds they form. Saturated hydrocarbons have one covalent carbon bond, for example, methane, propane, and butane are some of the saturated hydrocarbons as they have a single carbon covalent bond and unsaturated hydrocarbons on the other hand have either a double covalent carbon bond or a triple covalent carbon bond.
Unsaturated hydrocarbons are further divided into alkenes and alkynes based on the number of covalent bonds that the carbon atoms form. The hydrogenation reaction is the test used to figure out whether a compound is a saturated hydrocarbon or an unsaturated hydrocarbon. Hydrogenation is a type of reduction reaction where a hydrogen atom is added to a particular compound to know whether it is saturated or unsaturated. When the hydrogen atom is added to a compound it gets saturated and it tells us the previous stage of the compound.
The above article has discussed different properties, types, and uses of unsaturated hydrocarbons. Surely, this will help you understand and clarify your concepts on the topic.
FAQs on Unsaturated Hydrocarbons: Complete Guide for Students
1. What are unsaturated hydrocarbons?
Unsaturated hydrocarbons are organic compounds made entirely of carbon and hydrogen atoms, which contain at least one carbon-carbon double (C=C) or triple (C≡C) bond. Because of these multiple bonds, they have fewer hydrogen atoms than the maximum possible for their number of carbon atoms and can undergo addition reactions to become saturated. Common examples include ethene and propyne.
2. What is the main difference between saturated and unsaturated hydrocarbons?
The primary difference lies in the type of bonds between carbon atoms.
- Saturated hydrocarbons (like alkanes) contain only single covalent bonds between carbon atoms. They are relatively unreactive.
- Unsaturated hydrocarbons (like alkenes and alkynes) contain at least one double or triple covalent bond between carbon atoms. The presence of these multiple bonds, specifically the pi (π) bonds, makes them significantly more reactive than saturated hydrocarbons.
3. What are the main types of unsaturated hydrocarbons according to the CBSE syllabus?
As per the CBSE curriculum, the two main types of acyclic unsaturated hydrocarbons are:
- Alkenes: These hydrocarbons contain at least one carbon-carbon double bond. Their general formula is CₙH₂ₙ (for n ≥ 2). The simplest example is ethene (C₂H₄).
- Alkynes: These hydrocarbons are characterized by at least one carbon-carbon triple bond. Their general formula is CₙH₂ₙ₋₂ (for n ≥ 2). The simplest example is ethyne (C₂H₂).
4. What are some important examples and applications of unsaturated hydrocarbons?
Unsaturated hydrocarbons have several important real-world applications:
- Ethene (C₂H₄): Used as a raw material for producing polyethylene, a widely used plastic. It is also used as a plant hormone for artificially ripening fruits.
- Ethyne (C₂H₂): Commonly known as acetylene, it is used in oxy-acetylene torches for welding and cutting metals due to the high temperature of its flame.
- Propene (C₃H₆): A key component in the production of polypropylene plastic, used for making containers, car parts, and textiles.
5. How can you chemically test for unsaturation in a given hydrocarbon sample?
There are two common chemical tests to detect the presence of double or triple bonds:
- Bromine Water Test: When an unsaturated hydrocarbon is shaken with reddish-brown bromine water, the colour of the bromine water is discharged (it becomes colourless). This happens because the bromine undergoes an addition reaction across the multiple bond.
- Baeyer's Test: When an unsaturated hydrocarbon is treated with a cold, dilute, alkaline solution of Potassium Permanganate (KMnO₄), its pink colour fades and a brown precipitate of Manganese Dioxide (MnO₂) is formed.
6. How does the presence of double or triple bonds affect the reactivity of a hydrocarbon?
The presence of double (C=C) or triple (C≡C) bonds makes a hydrocarbon significantly more reactive. These multiple bonds consist of strong sigma (σ) bonds and weaker pi (π) bonds. The electrons in the pi bonds are more exposed and less tightly held, making them susceptible to attack by electrophiles. Consequently, unsaturated hydrocarbons readily undergo addition reactions, where the pi bond breaks and new atoms are added to the carbon atoms. Saturated hydrocarbons lack these pi bonds and are therefore much less reactive.
7. Why is ethene (C₂H₄) classified as an unsaturated hydrocarbon?
Ethene (C₂H₄) is classified as unsaturated because its structure contains a carbon-carbon double bond. According to the octet rule, a saturated two-carbon hydrocarbon (ethane) has the formula C₂H₆. Ethene has two fewer hydrogen atoms. To satisfy the valency of four for each carbon atom with only four hydrogens present, the two carbon atoms must share four electrons between them, forming a double bond. This double bond is the key feature of unsaturation, indicating that the molecule can potentially bond with more atoms.
8. What is the role of unsaturated hydrocarbons in biological systems like the human body?
In biological systems, the principles of unsaturation are crucial. Unsaturated fatty acids are key components of cell membranes and lipids. The 'kinks' created by cis-double bonds in their hydrocarbon chains prevent them from packing closely together. This increases the fluidity of cell membranes, which is essential for their proper function. Polyunsaturated fats, found in many oils, are considered healthier in diets compared to saturated fats for this reason.
9. Between an alkene and an alkyne with the same number of carbon atoms, which is more unsaturated and why?
An alkyne is more unsaturated than an alkene with the same number of carbon atoms. Unsaturation refers to the capacity to add more hydrogen atoms to become fully saturated.
- An alkene has one double bond (one pi bond) and can add one molecule of H₂ (two hydrogen atoms).
- An alkyne has one triple bond (two pi bonds) and can add two molecules of H₂ (four hydrogen atoms).
