What is Ethyne? Structure, Key Reactions & Real-World Uses
Build Your Concept By Referring to this Page Describing Ethyne
Organic chemistry is a universe of organic compounds. Studying their complex structures and behaviour is quite fascinating. In this segment, we will elaborately study Ethyne. It is also called acetylene. The triple bonded two carbon organic compound that behaves like gas at room temperature is called ethyne. The common name of ethyne is acetylene. The chemistry experts of Vedantu have scribed this concept page for the new learners. It falls in the hydrocarbon part of the organic chemistry chapters that should be properly studied to prepare a foundation. Refer to this page when you are studying ethyne and find an organized presentation of its structure, preparation, and chemical properties.
What is Ethyne or Acetylene?
Ethyne is the simplest triple-bonded 2 carbon organic compound, also known as acetylene. The IUPAC name of acetylene is ethyne. ‘Eth’ means ‘two’ and ‘yne’ means a triple bond between two carbon atoms. Together they make the IUPAC name and the meaning of ethyne. The acetylene formula is C2H2. As you can easily understand from the formula that it is a hydrocarbon as there are no elements other than carbon and hydrogen in the molecular structure.
Acetylene Structural Formula
The structure of ethyne makes it unstable in pure form. As per the structural formula of ethyne, the tension in the triple bond makes the carbon atoms increases as the bond angle is almost 180o. The length of the C-H bond is just 106 picometers whereas the C-C bond length is 120.3 picometers. It is an unsaturated hydrocarbon that cannot remain stable when stored in pure form. Every carbon atom is connected with a hydrogen atom at one end by a single bond and with another carbon atom with a triple bond. It is a symmetrical compound.
Another interesting aspect to learn on this concept page is the electron dot structure of ethyne. You will have to study and practice the electron dot structure of acetylene properly so that you can understand how the electrons are shared in every bond present in the molecule. Practising the electron dot structure will also help students understand how the compound is formed. This is also called the ethyne Lewis structure. This particular concept is ideal for students to understand how organic bonds are formed by sharing electrons. You will also learn how a carbon-hydrogen bond is formed and how the electrons are shared between two atoms of different elements.
Preparation of Ethyne
Now that you have studied the ethyne formula, let us move to the section where it is prepared. Study this section to understand how the triple bond is formed between the two carbon atoms. There are different ways to prepare acetylene. Ethyne can be prepared when methane is subjected to partial combustion at high pressure. Two methane (CH4) molecules connect forming a triple bond when the hydrogen atoms in the molecules get removed. The easiest way to prepare acetylene is by hydrolyzing calcium carbide (CaC2) simply in presence of water. Calcium carbide, also known as, calcium acetylide, quickly breaks in the presence of water due to the unstable bond and electron tension between the carbon molecules. The equation of this reaction is:
H2O + CaC2 → C2H2 + Ca(OH)2
If you consider the acetylene chemical formula, you will find that it is the final product along with calcium hydroxide. This is how acetylene is industrially produced on a large scale very easily and used for different purposes. You can now easily answer the question of how is ethyne prepared.
Properties of Acetylene/Ethyne
Let us proceed to the properties of ethyne. The physical and chemical properties of ethyne are:
The molecular mass or molar mass of this compound is 26.083 grams. You can also calculate it when you add the atomic mass of all the atoms in the molecular formula of acetylene.
Ethyne, under the standard condition of temperature and pressure (STP), behaves like a colourless gas. It also does not have any distinct odour.
The density of this gas is 1.097 g/l.
As you understood from the properties of ethyne that it is a gas, its melting point is -80.8°C or 192.3K.
Ethyne slightly dissolves in water.
FAQs on Ethyne: Preparation, Properties & Applications
1. What is ethyne, and what are its chemical formula and structure?
Ethyne, commonly known as acetylene, is the simplest alkyne with the chemical formula C₂H₂. Its structure features two carbon atoms connected by a triple bond (one sigma and two pi bonds) and each carbon atom is also bonded to one hydrogen atom. This results in a linear molecular geometry with a bond angle of 180°. The carbon atoms in ethyne are sp hybridised.
2. How is ethyne typically prepared in a laboratory setting?
In the laboratory, ethyne is most commonly prepared by the reaction of calcium carbide (CaC₂) with water. This process, known as hydrolysis, is straightforward and effective. When water is dripped onto lumps of calcium carbide, a vigorous reaction occurs, producing ethyne gas and calcium hydroxide as a by-product. The chemical equation for the reaction is: CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂.
3. What are the key physical and chemical properties of ethyne?
Ethyne has distinct physical and chemical properties that are important for students to know.
- Physical Properties: It is a colourless gas with a characteristic faint garlic-like odour when impure. It is sparingly soluble in water but highly soluble in organic solvents like acetone.
- Chemical Properties: Due to its triple bond, ethyne is highly reactive. It readily undergoes addition reactions (with hydrogen, halogens, hydrogen halides), shows a weak acidic character (reacting with strong bases like NaNH₂), and undergoes polymerisation reactions.
4. What are the most important applications of ethyne in industry?
Ethyne is a commercially important chemical with several key applications:
- Oxy-acetylene Welding and Cutting: When burned with pure oxygen, ethyne produces an extremely hot flame (around 3500°C), which is used for cutting and welding metals.
- Chemical Synthesis: It serves as a starting material for the synthesis of many organic compounds, including acetaldehyde, acetic acid, vinyl chloride (for PVC plastic), and acrylic acid.
- Artificial Ripening of Fruits: In some regions, ethyne gas is used as an artificial agent to ripen fruits like mangoes and bananas.
- Portable Lighting: Historically, it was used in carbide lamps for mining and other portable lighting applications due to its bright flame.
5. Why is ethyne significantly more acidic than ethene and ethane?
The higher acidity of ethyne compared to ethene and ethane is a direct result of its hybridisation. The carbon atoms in ethyne are sp hybridised, meaning they have 50% s-character. In contrast, ethene's sp² carbons have 33.3% s-character, and ethane's sp³ carbons have 25% s-character. The greater the s-character, the closer the electrons are held to the nucleus, increasing the electronegativity of the carbon atom. This increased electronegativity in ethyne pulls the C-H bond electrons closer to the carbon, making it easier for the hydrogen to be released as a proton (H⁺), thus making ethyne acidic.
6. How does the triple bond in ethyne influence its chemical reactivity compared to a double bond?
The triple bond in ethyne, consisting of one strong sigma (σ) bond and two weaker pi (π) bonds, is a region of high electron density. This makes ethyne highly susceptible to electrophilic addition reactions, similar to alkenes. However, alkynes are generally less reactive than alkenes towards electrophilic addition. This is because the sp hybridised carbons are more electronegative and hold the π electrons more tightly. Additionally, the formation of an intermediate vinylic carbocation is less stable. Thus, while ethyne undergoes addition reactions, it often requires more severe conditions or specific catalysts (e.g., mercuric sulphate for hydration).
7. Can you explain the polymerisation reaction of ethyne to form benzene?
Yes, ethyne can undergo cyclic polymerisation to form the aromatic compound benzene. This is a crucial reaction linking aliphatic and aromatic chemistry. When ethyne gas is passed through a red-hot iron tube at a high temperature of 873 K (600°C), three molecules of ethyne polymerise to form one molecule of benzene. This reaction is an important industrial method for synthesising benzene and its derivatives from non-aromatic precursors.
8. Why must ethyne be stored dissolved in acetone under pressure instead of being compressed directly as a gas?
Ethyne is a highly unstable and endothermic compound. When compressed on its own, it can decompose explosively into its constituent elements (carbon and hydrogen), releasing a significant amount of energy. To handle it safely, ethyne is dissolved in a solvent like acetone within a cylinder packed with a porous material. Acetone can dissolve large volumes of ethyne gas under pressure without the risk of explosive decomposition, making it stable and safe for transport and use in applications like welding.
