21. Preparation of Ethyne

Summary

This educational video demonstrates the preparation and examination of ethyne (C2H2), a colorless gas with a pungent odor. Ethyne is synthesized from calcium carbide, which often contains impurities like calcium sulfide and phosphide. The resulting ethyne gas is purified by passing it through acidified copper sulfate to remove contaminants. The video outlines safety precautions, such as avoiding contact with calcium carbide and using no open flames. It also covers tests for ethyne's properties, including its insolubility in water, solubility in organic solvents, and its reactivity with bromine and potassium permanganate, which indicate the presence of a carbon-carbon triple bond.

Takeaways

• 🔬 Ethine (C2H2) is prepared by reacting water with calcium carbide (CaC2), also known as calcium dicarbide.
• ⚠️ Calcium carbide is often impure, containing contaminants like calcium sulfide, phosphide, and nitride, which can affect the purity of ethine.
• 🌬️ The ethine produced may contain impurities such as hydrogen sulfide, phosphine, and ammonia, which are removed by passing the gas through acidified copper(II) sulfate.
• 👐 Handle calcium carbide with care, using a spatula to avoid initiating the reaction with moisture from hands.
• 🚫 Keep naked flames away from the gas preparation apparatus due to the risk of explosion when ethine mixes with air.
• 🔗 Ensure the gas washing bottle is correctly connected to prevent impure gases from being collected.
• 💧 Add water slowly to calcium carbide to control the rate of ethine production.
• 🧪 Ethine is a colorless gas that may have an unpleasant smell if impurities are present, and it is insoluble in water but soluble in organic solvents.
• 🔥 Ethine burns with a luminous, smoky flame and produces soot, indicating the presence of unburned carbon.
• 🌐 The addition of bromine water to ethine decolorizes the solution, demonstrating the reaction of the carbon-carbon triple bond with bromine.
• 🟣 Acidified potassium permanganate solution also decolorizes in the presence of ethine, showing another test for unsaturation due to the reactive triple bond.

Q & A

What is ethine and what is its chemical formula?

Ethine is a compound with the chemical formula C2H2, also known as acetylene.

What is the primary reactant used to prepare ethine in the described experiment?

The primary reactant used to prepare ethine in the experiment is calcium carbide (CaC2), also known as calcium dicarbide.

Why is calcium carbide often contaminated with other substances?

Calcium carbide is often contaminated with substances like calcium sulfide, calcium phosphide, and calcium nitride because it cannot be obtained in a pure state.

What are the safety precautions when handling calcium carbide?

When handling calcium carbide, one should not touch it with bare hands to avoid initiating the reaction with moisture, and a spatula should be used for transferring it. Also, no naked flame should be brought near the gas preparation apparatus due to the risk of explosion.

How are impurities in ethine gas removed during the experiment?

Impurities in ethine gas are removed by bubbling the gas through acidified copper(II) sulfate.

What is the purpose of the gas washing bottle in the experiment setup?

The gas washing bottle is used to ensure that the ethine gas is clean and free of impurities before it is collected and tested.

What physical properties of ethine are mentioned in the script?

Ethine is described as a colorless gas that is insoluble in water but soluble in organic solvents.

How is the combustion test for ethine performed, and what is observed?

The combustion test is performed by bringing a lit taper to the mouth of a gas jar containing ethine. It burns with a luminous, smoky flame, and a great deal of soot is formed due to unburned carbon.

What happens when ethine reacts with bromine water, and why?

When ethine reacts with bromine water, the yellow color disappears because the very reactive carbon-carbon triple bond in ethine reacts readily with the bromine.

What is the purpose of adding acidified potassium permanganate to ethine, and what is observed?

Adding acidified potassium permanganate to ethine is used to test for unsaturation. The purple color of the potassium permanganate disappears, indicating a reaction with the carbon-carbon triple bond in ethine.

Why is it important to perform tests on ethine away from the apparatus?

Tests on ethine should be performed away from the apparatus because ethine gas forms an explosive mixture with air, and conducting tests near the apparatus could be dangerous.

Outlines

00:00

🔬 Preparation and Collection of Ethyne

The video script describes an experiment to prepare ethyne (C2H2) by reacting water with calcium carbide (CaC2), also known as calcium dicarbide. It is noted that calcium carbide is often contaminated with other compounds like calcium sulfide, phosphide, and nitride, which can contaminate the ethyne with gases such as hydrogen sulfide, phosphine, and ammonia. To purify the ethyne, the gas is bubbled through acidified copper(II) sulfate. The setup of the experiment is detailed, emphasizing safety precautions such as avoiding contact with calcium carbide and not using naked flames near the apparatus due to the explosive nature of ethyne when mixed with air. The process involves adding water slowly to calcium carbide to produce ethyne, which is collected in test tubes and gas jars. The reaction's equation is displayed on the screen.

05:13

🔍 Testing the Properties of Ethyne

This part of the script focuses on testing the physical properties and reactions of ethyne. It is observed that ethyne is a colorless gas, which may have an unpleasant smell if impurities are present. Unlike methane, ethyne is insoluble in water but soluble in organic solvents. A combustion test is conducted, where ethyne burns with a luminous, smoky flame, producing soot due to unburned carbon. The script also details tests for unsaturation in ethyne: the addition of bromine water, which decolorizes indicating a reaction with the carbon-carbon triple bond, and the addition of acidified potassium permanganate, which also decolorizes due to the same reactive bond. The script clarifies that the specific reaction equations and product names are not required knowledge for the course, and thus, they are not discussed further. The segment concludes with a summary of the study on the properties of ethyne.

Keywords

💡Ethine

Ethine, also known as acetylene, is an organic compound with the chemical formula C2H2. It is a colorless and highly flammable gas that is insoluble in water but soluble in organic solvents. In the video, ethine is prepared by reacting water with calcium carbide, and its preparation and properties are the central theme. The script describes how ethine is contaminated with other gases during its preparation, which are then removed through a purification process.

💡Calcium Carbide

Calcium carbide is a chemical compound with the formula CaC2. It is used industrially in the production of ethine. The script mentions that calcium carbide is often contaminated with other compounds such as calcium sulfide, calcium phosphide, and calcium nitride, which can affect the purity of the ethine produced. The video emphasizes the importance of handling calcium carbide with care, as it can initiate the reaction with moisture.

💡Copper(II) Sulfate

Copper(II) sulfate is a chemical compound that is used in the purification process of ethine. In the video, it is mentioned that ethine gas is bubbled through acidified copper(II) sulfate to remove impurities such as hydrogen sulfide, phosphine, and ammonia. This step is crucial for obtaining a purer form of ethine for further experimentation.

💡Combustion

Combustion is a chemical reaction that involves the reaction of a substance with oxygen, producing heat and light. In the context of the video, the combustion of ethine is demonstrated by igniting the gas in a jar, which results in a luminous, smoky flame and the formation of soot. This experiment illustrates ethine's flammability and the presence of unburned carbon in the form of soot.

💡Bromine Water

Bromine water is a solution of bromine in water, which is used as a test for unsaturation in organic compounds. In the script, bromine water is added to ethine to demonstrate its reactivity due to the presence of a carbon-carbon triple bond. The disappearance of the yellow color of bromine water indicates that a reaction has occurred, which is a key observation in the video.

💡Potassium Permanganate

Potassium permanganate is a strong oxidizing agent often used in chemical tests. In the video, it is used to test for the presence of unsaturation in ethine. The script describes how the purple color of potassium permanganate solution disappears when it is added to ethine, indicating a reaction has taken place due to the reactive triple bond in ethine.

💡Carbon-Carbon Triple Bond

A carbon-carbon triple bond is a covalent bond between two carbon atoms, consisting of three shared electron pairs. Ethine is characterized by having a triple bond, which makes it highly reactive. The video script describes how this bond reacts readily with bromine water and potassium permanganate, which are tests for unsaturation.

💡Flask

A flask is a type of laboratory glassware used for containing and mixing substances. In the video, a flask is used to hold calcium carbide during the preparation of ethine. The script cautions against touching the calcium carbide with hands to prevent premature reaction and emphasizes the use of a spatula for transferring the substance.

💡Fume Cupboard

A fume cupboard is a laboratory safety device that protects users from hazardous fumes by drawing them away from the user and into an exhaust system. In the script, the fume cupboard is mentioned as the location where the combustion test of ethine is performed, highlighting the importance of safety precautions when handling flammable gases.

💡Spatula

A spatula is a laboratory tool used for scooping, transferring, and spreading substances. The video script advises using a spatula to handle calcium carbide to avoid initiating a reaction with the moisture from hands, demonstrating the importance of proper laboratory techniques.

💡Impurities

Impurities refer to unwanted substances that are mixed with a main substance. In the context of the video, ethine prepared from calcium carbide often contains impurities such as hydrogen sulfide, phosphine, and ammonia. The script describes the process of removing these impurities to obtain purer ethine, which is essential for accurate experimental results.

Highlights

Ethine (C2H2) is prepared by the reaction of water with calcium carbide (CaC2).

Calcium carbide is contaminated with calcium sulfide, phosphide, and nitride, affecting ethine purity.

Impurities in ethine include gases like hydrogen sulfide, phosphine, and ammonia.

Acidified copper(II) sulfate is used to remove impurities from ethine gas.

Apparatus setup instructions emphasize safety, avoiding contact with calcium carbide and naked flames.

Ethine gas forms an explosive mixture with air, necessitating careful handling.

Gas washing bottle connections must be double-checked for safety.

The reaction equation for ethine formation is displayed during the experiment.

Physical properties of ethine include being colorless, smelling unpleasant if impure, and insoluble in water.

Ethine is soluble in organic solvents due to its chemical structure.

Combustion tests of ethine show a luminous, smoky flame with soot formation.

Bromine water test indicates ethine's unsaturation by the disappearance of the yellow color.

The addition of acidified KMnO4 to ethine results in a colorless solution, demonstrating unsaturation.

The carbon-carbon triple bond in ethine is very reactive and readily reacts with bromine and potassium permanganate.

Students are not required to know the reaction equations or product names for the bromine and KMnO4 tests.

The study concludes with an overview of ethine's properties and the experimental procedures.

Transcripts

[Music]

experiment to prepare ethine and examine

its

properties ethine C2 H2 is prepared by

the reaction of water with a substance

called calcium carbide

ca2 calcium carbide is also called

calcium

dicarbide calcium carbide cannot be

obtained in a pure state it is usually

contaminated with calcium sulfide

calcium phosphide and calcium nitride as

a result the ethine obtained from it

usually is contaminated with gases like

hydrogen sulfide phosphine and

ammonia these gases are removed by

bubbling the gas through acidified

copper 2

sulfate set up the apparatus as

shown do not touch the calcium carbide

with your fingers as moisture from your

hands could start the reaction

use the spatula when transferring the

calcium carbide to the

flask no naked flame should be brought

anywhere near the gas preparation

apparatus ethine gas forms an explosive

mixture with air tests on the gas should

be performed well away from the

apparatus

double check that you have connected the

gas washing bottle

correctly

using the dropping funnel Add Water

slowly to the calcium carbide to

maintain an even not too vigorous

evolution of

etin

collect some test tubes and a few gas

jars of the

gas

for

e

just

the equation for the reaction is shown

on the

screen note the formation of white

calcium hydroxide inside the flask place

your hand on the outside of the

flask when you perform this experiment

yourself

write down what you

notice in the next part of the

experiment we will carry out a number of

tests on the

gas note the physical properties of

ethine it is a colorless gas with the

smell if impurities are still present it

will not smell very

nice like methane and

ethine ethine is insoluble in water but

soluble in organic

solvents

combustion if your teacher allows it

bring the gas jar of ethine to the fume

cupboard remove the gas jar cover and

apply a lighted taper to the mouth of

the gas

chair note that it burns with a luminous

Smoky flame and a great deal of soot is

formed the so is formed as a result of

unburned

carbon addition of bromine as in the

case of the preparation of ethine

bromine can be used to test for

unsaturation at about 110 of a test tube

of broing water to a test tube of

ethine replace the stopper and shake the

test tube a few

times note that the yellow color

disappears the very reactive

carboncarbon triple bond reacts readly

with the

you are not required to know the

equation of the reaction or the names of

the products for this

course addition of acidified

km4 as in the case of the preparation of

ethane potassium permanganate can be

used to test for

unsaturation add about one1 of a test

tube of potassium permanganate to a test

tube of

e replace the stopper and shake the test

tube a few times

note that the purple color disappears

and a colorless solution is

obtained the very reactive carboncarbon

triple bond reacts readly with the

potassium

permanganate you are not required to

know the equation of this reaction are

the names of the products for this

course hence it will not be discussed

further this concludes the study of the

properties of

ethine

[Music]