Q2. * Preparation and properties of ethene Flashcards
In general how will you prepare ethene?
By dehydrating ethanol (removing the elements of water from ethanol)
What substance acts as the dehydrating agent in this experiment?
Aluminium oxide
What is the formula for aluminium oxide?
Al2O3
Describe the appearance of aluminium oxide.
A white powder
What is Al2O3?
Aluminium oxide
What acts as the catalyst for this experiment?
Aluminium oxide
What type of reaction is the dehydration of ethanol to produce ethene called?
An elimination reaction
What equipment is required for this apparatus?
4
Boiling tube
One-hole rubber stopper
Delivery tube
Trough
What chemicals are needed for this experiment?
6
Ethanol
Aluminium oxide
Limewater
Glass wool
Bromine water
Acidified potassium permanganate solution (very dilute)
What colour should the acidified potassium permanganate be?
It should be pale purple
Why is the acidified potassium permanganate you used pale purple?
Because it should be very dilute
What is the first step in this experiment?
Pour some ethanol into a boiling tube to a depth of about 2-3cm
Where should the ethanol be placed?
It should be poured into a boiling tube
What is the second step in this experiment, the ethanol has just been poured into the boiling tube.
(3)
Add some glass wool to soak up the ethanol
Use a glass rod to push the glass wool down the boiling tube
The glass wool is used to hold the ethanol in place while the reaction to produce ethene is occurring
What is used to soak up the ethanol?
Glass wool
How should the glass wool be placed in the boiling tube?
Use a glass rod to push the glass wool down the boiling tube
What is the function of the glass wool?
It is used to hold the ethanol in place while the reaction to produce ethene is occurring
What is the third step in this experiment, the glass wool has just been soaked in the ethanol?
Using a retort stand, clamp the boiling tube near its mouth and in a horizontal position
What should be used to clamp the boiling tube?
A retort stand
Where exactly should the retort stand clamp the boiling tube?
Near its mouth and in a horizontal position
What should the retort stand be used to clamp?
The boiling tube
What is the fourth step in this experiment, the boiling tube has just been clamped on the retort stand?
Using a spatula, place a small heap of aluminium oxide about halfway along the boiling tube
What should be used to place the aluminium oxide in the boiling tube?
A spatula
What should be placed halfway along the boiling tube?
Aluminium oxide
Where exactly should the aluminium oxide be placed?
It should be placed halfway along the boiling tube
What is the fifth step of this experiment, the aluminium oxide has just been placed in the boiling tube?
(6)
Set up the apparatus
Boiling tube clamping near the mouth horizontally by the retort stand
Place aluminium oxide halfway along the boiling tube
Stopper boiling tube with a one-hole rubber stopper
Connect the delivery tube to the rubber stopper and lead it to the upside down tube inside the trough of water
Light a Bunsen burner directly under the aluminium oxide
What is the sixth step of the experiment, the apparatus has just been set up?
(4)
Light the Bunsen burner and adjust it to give a blue flame and gently heat the aluminium oxide
As the aluminium oxide becomes hot, the heat reaches the ethanol at the end of the boiling tube
The ethanol changes into a vapour, passes over the hot aluminium oxide, and is dehydrated to form ethene
If the ethene is bubbling off too slowly, move the Bunsen burner nearer the ethanol for a brief moment
How should you adjust the Bunsen burner?
Adjust it to give a blue flame
What should the Bunsen burner be used to heat?
The aluminium oxide
What happens as the aluminium oxide becomes hot?
2
The heat reaches the ethanol at the end of the boiling tube
This causes the ethanol to change into a vapour which passes over the hot aluminium, and is dehydrated to form ethene
What should you do if the ethene is bubbling off too slowly?
You should move the Bunsen burner nearer the ethanol for a brief moment
What is the seventh step of this experiment, ethene gas is bubbling off?
(2)
Allow the bubbles to escape for a short while, as these are mainly bubbles of air displaced from the apparatus
Collect five test-tubes of the gas-put a stopper on each tube as it is filled
Why should you allow the bubbles to escape for a short while?
As these are mainly bubbles of air displaced from the apparatus
How many test-tubes of the gas should you collect?
Five test-tubes
How should you collect the gas?
Collect five test-tubes of the gas-put a stopper on each tube as it is filled
What is the eight step of this experiment, five test tubes of the gas have just been gathered?
(4)
When all the test-tubes have been filled, loosen the boss head on the retort stand and raise the apparatus up so that the delivery tube is no longer dripping into the water
Then turn off the Bunsen burner
If the delivery tube were simply left in the water trough, a suck-back of water would occur because 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
What should you do when all the tubes have been filled?
3
Loosen the boss head on the retort stand
Raise the apparatus up so that the delivery tube is no longer dripping into the water
Then turn off the Bunsen burner
Why should you raise the apparatus up so that the delivery tube is no longer dripping into the water?
If the delivery tube were simply left in the water trough, a suck-back of water would occur because the boiling tube begins to cool as soon as the Bunsen burner is turned off
What two things can be prevented by taking apart the apparatus properly?
(2)
You can prevent the suck-back of water into the boiling tube
You can prevent the glass of the boiling tube cracking from the cold water
What is the ninth step of this experiment, you have just taken apart the apparatus?
(5)
Note the physical properties of ethene
It is a colourless gas
Has a sweetish smell
Insoluble in water
Dissolves in organic solvents such as hexane or chloroform
List the physical properties of ethene
4
It is a colourless gas
Has a sweetish smell
Insoluble in water
Dissolves in organic solvents such as hexane or chloroform
What proves ethene is insoluble in water?
2
The fact that the gas can be collected over water shows clearly that it is insoluble in water
If it was soluble in water the gas would simply dissolve in water instead of bubbling through it
Give two substances that ethene dissolves in.
Hexane
Chloroform
What is the tenth step of this experiment, you have just noted the physical properties of ethene?
(6)
Combustion test
Remove the stopper from one of the test-tubes and, using a lighted wax taper, apply a light to the mouth of the test-tube
Note that the gas burns with a luminous flame
Allow the gas to burn
When it has stopped burning, add some limewater to the test-tube, stopper it and shake the test-tube a few times
The limewater turns milky, showing that carbon dioxide has been formed when ethene burns in air
How should you carry out the combustion test?
2
Remove the stopper from one of the test-tubes
Using a lighted wax taper, apply a light to the mouth of the test-tube
How does ethene burn?
It burns with a luminous flame
What should you do when the ethene stops burning?
Add some limewater to the test-tube, stopper it and shake the test-tube a few times
What happens when you add limewater is added to the test tube after the ethene has been burned?
The limewater turns milky
What does it mean if limewater turns milky?
The limewater turns milky, showing that carbon dioxide has been formed when ethene burns in air
What is the eleventh step of this experiment, you have just carried out the combustion test?
(3)
Add one-tenth of a test-tube of bromine water to a test-tube of ethene.
Replace the stopper and shake the test-tube a few times
Colour change from red to colourless
How much bromine water should you add to the ethene?
One-tenth of a test-tube
What colour change takes place when bromine water is added to ethene?
Red to colourless
What is the twelfth step of this experiment, you have just added bromine water to ethene?
(3)
Add one-tenth of a test-tube of acidified potassium permanganate to a test-tube of ethene.
Replace the stopper and shake the test-tube a few times
Colour change from pale purple to colourless
What colour change takes place when you add acidified potassium permanganate to a test-tube of ethene?
Colour change from pale purple to colourless
