20. Preparation of Ethene

Summary

This experiment focuses on the preparation and examination of ethene, a colorless gas, by dehydrating ethanol using aluminum oxide as a dehydrating agent and catalyst. The process involves heating ethanol in a boiling tube, collecting ethene gas over water, and observing its properties. Ethene's insolubility in water, combustion to form carbon dioxide and water, and reactivity with bromine water and potassium permanganate are demonstrated, confirming the presence of a carbon-carbon double bond.

Takeaways

• 🧪 The experiment involves preparing a sample of ethene gas by dehydrating ethanol using aluminum oxide (Al2O3) as a dehydrating agent and catalyst.
• 🔥 A Bunsen burner is used to gently heat the aluminum oxide, which initiates the dehydration reaction at the end of the boiling tube where ethanol is held by glass wool.
• 🌡️ The boiling tube is positioned horizontally to ensure the ethene gas produced can be collected over water.
• 💧 Ethene is insoluble in water, which is demonstrated by its ability to be collected over water without dissolving.
• 🔥 Ethene burns with a flame, indicating it is flammable, and when burned in air, it forms carbon dioxide and water.
• 🥛 The presence of carbon dioxide after burning ethene is confirmed by adding limewater, which turns milky due to the formation of calcium carbonate.
• 🌿 Bromine water is used to test for unsaturation in organic compounds; the disappearance of the yellow color indicates the presence of a carbon-carbon double bond in ethene.
• 🧪 The addition of bromine across the double bond in ethene results in the formation of a colorless compound, 1,2-dibromoethane.
• 🌿 Potassium permanganate (KMnO4) is also used as a test for unsaturation, and its decolorization upon reaction with ethene confirms the presence of a carbon-carbon double bond.
• 📚 The experiment concludes with a demonstration of the chemical properties of ethene, highlighting its reactivity due to the presence of a carbon-carbon double bond.

Q & A

What is the purpose of the experiment described in the transcript?

The purpose of the experiment is to prepare a sample of ethene gas by dehydrating ethanol using a chemical reaction and to examine its properties.

Which substance is used as a dehydrating agent and catalyst in the experiment?

Aluminium oxide (Al2O3) is used as a dehydrating agent and catalyst in the experiment.

How is the boiling tube positioned during the reaction?

The boiling tube is clamped near its mouth and positioned horizontally during the reaction.

What is the role of glass wool in the experiment?

Glass wool is used to hold the ethanol in place while the reaction takes place.

How is the gas collected in the experiment?

The gas is collected over water, indicating that ethene is insoluble in water.

What happens when ethene is burned?

When ethene is burned, it produces a flame and carbon dioxide, which turns limewater milky.

What is the significance of the color change in bromine water when added to ethene?

The disappearance of the yellow color in bromine water indicates the presence of unsaturation, such as a carbon-carbon double bond, in the ethene molecule.

How does potassium permanganate (KMnO4) test for the presence of a carbon-carbon double bond in ethene?

The disappearance of the purple color of potassium permanganate to give a colorless solution is evidence for the presence of a carbon-carbon double bond in ethene.

What is the expected product when bromine is added to ethene?

The expected product when bromine is added to ethene is a colorless oily compound called 1,2-dibromoethane.

Why is it important to remove the delivery tube from the water after collecting the gas?

It is important to remove the delivery tube from the water to prevent a siphoning effect, which could occur if the boiling tube cools and the water is sucked back into the tube, potentially causing it to crack.

What general rule is followed when organic compounds like ethene burn in air?

When organic compounds like ethene burn in air, they generally form carbon dioxide and water.

Outlines

00:00

🔬 Preparing Ethane Gas from Ethanol

In this segment, the experiment focuses on preparing a sample of ethane gas by dehydrating ethanol. Ethanol is dehydrated using a chemical reaction facilitated by aluminum oxide (Al2O3), which acts as both a dehydrating agent and a catalyst. The process begins with pouring ethanol into a boiling tube, adding glass wool to contain the liquid, and then placing aluminum oxide along the tube. The setup includes a Bunsen burner for heating and a collection apparatus for capturing the gas. The reaction is initiated by heating the aluminum oxide, which in turn heats the ethanol, causing it to vaporize and react with the aluminum oxide to form ethane gas. The gas is collected over water, indicating that ethane is insoluble in water. The experiment also involves careful handling to prevent air bubbles and to ensure the collection of pure ethane gas samples.

05:02

🔍 Investigating the Properties of Ethane

This part of the experiment investigates the physical properties of ethane, a colorless and odorless gas. The insolubility of ethane in water is demonstrated by its ability to be collected over water. The experiment proceeds to examine the combustion of ethane, noting that it burns with a characteristic flame and produces carbon dioxide, which is confirmed by the limewater turning milky. The presence of a carbon-carbon double bond in ethane is tested using bromine water and potassium permanganate (KMnO4). The addition of bromine water to ethane results in a colorless compound, indicating the formation of 1,2-dibromoethane, and the disappearance of the bromine water's yellow color signifies the presence of unsaturation in the ethane molecule. Similarly, the addition of potassium permanganate and its subsequent decolorization provides further evidence of the carbon-carbon double bond in ethane.

Keywords

💡Ethanol

Ethanol is an organic compound with the chemical formula C2H5OH, commonly known as alcohol. In the script, ethanol is used as a starting substance that undergoes a dehydration reaction to produce a hydrocarbon called ethylene. The process involves heating ethanol in the presence of a dehydrating agent to remove water molecules, which is a key step in the experiment described.

💡Dehydration

Dehydration in chemistry refers to the removal of water from a substance. In the context of the video, dehydration is a chemical reaction where ethanol is heated to remove water molecules, forming ethylene. This process is facilitated by a dehydrating agent, which in this case is aluminum oxide.

💡Aluminium Oxide (Al2O3)

Aluminium oxide, with the chemical formula Al2O3, is a white powdery substance used in the script as a dehydrating agent and catalyst. It plays a crucial role in the dehydration of ethanol, where it helps to remove water and catalyze the formation of ethylene. The script describes placing aluminium oxide in a boiling tube with ethanol to initiate the reaction.

💡Boiling Tube

A boiling tube is a piece of laboratory glassware used for heating small quantities of substances. In the script, a boiling tube is filled with ethanol and used to contain the reaction mixture. The tube is heated to facilitate the dehydration reaction, and its horizontal position is crucial for the proper collection of the resulting ethylene gas.

💡Glass Wool

Glass wool is a fibrous material made from glass that is used in laboratories to hold substances in place, especially during heating processes. In the script, glass wool is added to the boiling tube to hold the ethanol in place while the reaction occurs, preventing it from spilling or splashing out.

💡Bunsen Burner

A Bunsen burner is a type of gas burner used in laboratories to provide a controlled heat source. In the video script, a Bunsen burner is used to gently heat the aluminum oxide, which in turn heats the ethanol to initiate the dehydration reaction and produce ethylene.

💡Gas Collection Over Water

Collecting gas over water is a method used in laboratories to collect gases that are insoluble in water. In the script, ethylene gas is collected over water because it is insoluble in water, allowing it to be collected as bubbles without dissolving.

💡Bromine Water

Bromine water is a solution of bromine in water, which has a characteristic yellow color. It is used as a test for unsaturation in organic compounds, such as the presence of carbon-carbon double bonds. In the script, bromine water is added to ethylene to demonstrate its reactivity, as the disappearance of the yellow color indicates the formation of a new compound, dibromoethane.

💡Potassium Permanganate (KMnO4)

Potassium permanganate is a strong oxidizing agent with the chemical formula KMnO4. It is used in the script to test for the presence of carbon-carbon double bonds by adding it to ethylene. The disappearance of the purple color of the potassium permanganate solution upon reaction with ethylene confirms the presence of a double bond.

💡Carbon-Carbon Double Bond

A carbon-carbon double bond is a covalent bond between two carbon atoms where each carbon atom contributes two electrons to the bond. This type of bond is characteristic of alkenes, and in the script, the presence of such a bond in ethylene is confirmed through reactions with bromine water and potassium permanganate.

💡Lime Water

Lime water is a solution of calcium hydroxide in water, which turns milky in the presence of carbon dioxide due to the formation of calcium carbonate. In the script, lime water is used to test the combustion products of ethylene, where the formation of carbon dioxide is indicated by the cloudiness of the lime water.

Highlights

Preparation of a thin gas sample by dehydrating ethanol using a chemical reaction.

Use of aluminum oxide (Al2O3) as a dehydrating agent and catalyst in the reaction.

Ethanol is dehydrated to form a new substance over heated aluminum oxide.

Collection of the gas over water, indicating the gas is insoluble in water.

Burning of the gas produces a blue flame, indicating it is an alkene.

Addition of lime water turns milky, confirming the formation of carbon dioxide upon burning.

Bromine water decolorization upon reaction with the gas, indicating the presence of unsaturation.

Formation of a new colorless compound, 1,2-dibromoethane, upon addition of bromine.

Use of potassium permanganate to test for the presence of carbon-carbon double bonds.

Disappearance of purple color in potassium permanganate solution confirms the presence of a double bond.

General rule that organic compounds burn in air to form carbon dioxide and water.

Reactivity of alkenes due to the presence of carbon-carbon double bonds.

Bromine adds across the carbon-carbon double bond to form 1,2-dibromoethane.

Bromine water is commonly used as a test for unsaturation in compounds.

The study concludes with the successful identification of the properties of the alkene.

Transcripts

experiments to prepare eating and

examine its properties in this

experiment we will prepare a sample v

thin gas by dehydrating a substance

called ethanol others using a chemical

reaction to remove the elements of water

from ethanol a white powder called

aluminium oxide al2o3 is used in to

reaction this substance acts as a

dehydrating agent and also as catalyst

the reaction some ethanol was poured

into a boiling tube to a depth of about

two to three centimeters some glass wool

was added to soak up the ethanol glass

wool is used to hold the ethanol in

place while the reaction to produce at a

theme is a crane using a retort stand

the boiling tube is camp near its most

and in a horizontal position as shown

using a spatula a heap of aluminium

oxide is placed about halfway along the

boiling tube the apparatus collecting

gas is set up as shown and the gas is

collected over watering light the Bunsen

burner

adjusted to give a brief flame and

gently heat the aluminum oxide

at the aluminum oxide comes fast the

heat reaches the ethanol at the end of

the tube the a smell changes into a

vapor passes over the heart aluminium

oxide and is dehydrated form a scene if

the e teen is bubbling off T slowly

moved once in Burnet near the edge now

for a bridge moment allow the bubbles to

escape for a short one as these are

mainly bubbles of air displaced from the

apparatus

collect five tattoos of the gas

put a stopper on each test tube as it is

filled

when all the test Chiefs have been

filled leasing the boss head on the

reach our stand and raise the apparatus

up so that the delivery cheap is no

longer dipping into the water then turn

off the Bunsen burner if the delivery

cheap were simply left in the water

trust a suck lack of water would occur

since the boiling tube begins to cool as

soon as the Bunsen burner is turned off

the cold water could cause the hot

boiling tube to crack in the next part

of this experiment we will examine

proxies VP note the physical properties

of eating it is the colorless gas with

Swedish Sloan the fact that the gas can

be collected over water shows clearly

that is insoluble in water otherwise gas

would simply dissolve in the water

instead the bubble insurance we now

investigate what happens when we burn

easy remove the lid from one of the gas

chains and use the latest wax paper

apply a light the most of the gas turn

note that the gas burns would leave them

the flame allow the gas to burn when it

is soft burning add some lame water to

the gas sir

replace the lid and shake the gas share

a few times

limewater turns milky showing the carbon

dioxide has been formed when a teen

burns an area eating burns to form

carbon dioxide mortar accordance with

equations shown on screen as a general

rule or organic compounds burn and air

to form carbon dioxide and water

addition of bromine alkenes are more

reactive than alkenes because of the

presence of the carbon-carbon double

bond in alkenes

for example bromine adds across the

carbon-carbon double bond to form a

colourless oily compound called one to

die bromomethane a solution of bromine

and water is commonly called bromine

water let's see what happens if we add

some bromine water to a test tube of

eating replace the stopper and shake the

test tube a few times

note that the yellow color of the Birman

water solution disappears what happens

here is that a new colorless compound

called to bromo ethanol is formed the

loss of the yellow color from bromine is

standard test for unsaturation in a

compound in other words this test shows

us that there is either carbon carbon

double bonds or a carbon-carbon triple

bond in the ec molecule potassium

permanganate kmno4 is also used to test

for the presence of the carbon-carbon

double bond anything add about 1/10 of

test tube of dilute kmno4 to a test tube

of 18 shake the test tube a few times

the disappearance of prayerful colors to

give the colorless solution is evidence

for the presence of a carbon-carbon

double bond this concludes the study of

proxies movie theme

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