Science - Chemistry - Organic Chemistry - 2 Hydrocarbons
(P7171100)
2.5 The characterization of ethine
Experiment by: anouch
Printed: Feb 20, 2014 10:23:55 AM
interTESS (Version 13.12 B214, Export 2000)
Task
Task
What is meant by the term "unsaturated" hydrocarbons? (2)
Prepare acetylene and examine some of its properties.
Use the space below for your own notes.
Logged in as a teacher you will find a button below for additional information.
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Additional Information
Learning objectives
• Acetylene can be prepared by the reaction of calcium carbide with water.
• Acetylene is an "unsaturated" and therefore relatively reactive hydrocarbon, which
belongs to the alkyne group.
Notes on setup and procedure
Preparation:
The reaction proceeds more slowly when sodium chloride solution is used instead of
water. With older calcium carbide which shows little reaction, hydrochloric acid can
be used instead of water. Prepare fresh potassium permanganate solution made
alkaline with soda (add 5% potassium permanganate solution to 10% sodium carbonate
solution until it has a light violet colour).
Remarks on the students experiments:
Mixtures of acetylene and air are explosive over a wide concentration range. Check
that there are no leaks in the apparatus and that all open flames are extinguished
when the gas is evolved. Stop the experiment immediately when the test tubes are
filled, as otherwise too much odor nuisance will be caused by the phosphine which
is generated. Disassemble the apparatus in the fume hood. Use the test tube which
was filled second to test the combustibility of acetylene.
Hazard and precautionary statements
Potassium permanganate:
H272:May intensify fire; oxidizer.
H302:Harmful if swallowed.
H410:Very toxic to aquatic life with long lasting effects.
P210: Keep away from heat/sparks/open flames/hot surfaces – No smoking.
P273: Avoid release to the environment.
P501: Dispose of contents/ containers to be collected by a licensed contractor in
accordance with national and local regulations.
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Sodium carbonate:
H319:
Causes serious eye irritation.
P260:
Do not breathe dust.
P305 + P351 + P338:IF IN EYES: Rinse cautiously with water for several minutes.
Remove contact lenses if present and easy to do – continue
rinsing.
P501:
Dispose of contents/ containers to be collected by a licensed
contractor in accordance with national and local regulations.
Calcium carbide:
H260:
In contact with water releases flammable gases which may ignite
spontaneously.
P233:
Keep container tightly closed.
P231 + P232:Handle under inert gas. Protect from moisture.
P370 + P378:In case of fire: Use carbon dioxide for extinction
P501:
Dispose of contents/ containers to be collected by a licensed contractor
in accordance with national and local regulations.
Hazards
• Explosive gases are evolved during the experiment. Air the room well after the
experiment!
• Do not allow calcium carbide to get on your skin, wear protective glasses!
• During the evolution of gas, extinguish all open flames!
• To make glass/rubber connections, wet the glass with glycerol so it can be easily
inserted!
Notes
Calcium carbide can be regarded as the salt of the very weak acid acetylene. The
process which took place would accordingly be the hydrolysis of this salt. Acetylene
has a relatively good solubility in water. It is therefore often recommended in the
literature that it be collected under a concentrated sodium chloride solution . This is
not necessary here, as the quantities of the used reagents are sufficient for the
formation of the required volume of gas.
Remarks on the method
The homologous series of the alkynes can be developed just as it was done for the
alkanes.
Advanced courses: The good solubility and the acidic character of acetylene can be
discussed. During the discussion the mesomeric effect and the polarizability of the
triple bond can be discussed.
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Waste disposal
• Allow the calcium carbide to react completely (maybe add more water), then
pour the liquid into the acid and alkali waste container.
• Pour potassium permanganate solution also into the acid and alkali waste
container.
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Material
Material
Material from "TESS advanced Chemistry Set Organic Chemistry, CH-4 " (Order
No. 15304-88)
Position No. Material
Order No. Quantity
1
Support base, variable
02001-00
1
2
Support rod, l = 370 mm, d = 10 mm
02059-00
1
3
Test tube brush w. wool tip, d = 25 mm
38762-00
1
4
Spoon spatula, special steel
33398-00
1
5
Rubber stopper, d = 22/17 mm, 1 hole
39255-01
1
6
Wash bottle, plastic, 250 ml
33930-00
1
7
Test tube rack for 12 tubes, holes d = 22 mm, wood
37686-10
1
8
Universal clamp
37715-00
1
9
Test tube, 180x18 mm
37658-10
(2)
10
Test tube, 180x20 mm, DURAN®, PN19
36293-00
1
11
Rubber stopper, d = 22/17 mm, without hole
39255-00
2
12
Rubber tubing, i.d. 6 mm
39282-00
1
13
Boss head
02043-00
1
14
Protecting glasses, clear glass
39316-00
1
15
Glass tube, right-angled, 85 x 60
36701-52
1
16
Glass tube, straight with tip, 200 mm
36701-63
1
17
Dish, plastic, 150x150x65 mm
33928-00
1
Chemicals, Additional Material
Position No. Material
Order No. Quantity
Bunsen burner /DIN/, nat.g., w. cock
32168-05
1
Safety gas tubing, DVGW, sold per metre
39281-10
1
Glycerol, 99%, 250 ml
30084-25
Potassium permanganate, 250 g
30108-25
Sodium carbonate, anhyd., 1000 g
30154-70
Water, distilled, 5 l
31246-81
Calcium carbide, granulated, 250 g
48018-25
Material required for the experiment
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Setup
Setup
Hazards
•
•
•
•
Explosive gases are evolved during the experiment. Air the room well after the experiment!
Do not allow calcium carbide to get on your skin, wear protective glasses!
During the evolution of gas, extinguish all open flames!
To make glass/rubber connections, wet the glass with glycerol so it can be easily inserted!
Setup
Set up the stand as shown in Fig. 1 to 4.
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Put a spoonful of calcium carbide in the Duran test tube and fix it on the stand at a slight angle
(Fig. 5).
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Fig. 5
Connect the right-angled glass tube to the untipped end of the straight glass tube with a piece
of rubber tubing. Ease the free end of the right-angled glass tube through the hole of the
rubber stopper (wet the glass with glycerol!) with a gentle screwing motion (Fig. 6)
Fig. 6
Fill the plastic dish two thirds full with tap water. Fill the two test tubes with water, close them
with your thumb and position them upside down in the dish (Fig. 7+8).
Fig. 7
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Fig. 8
Action
Action
Procedure
Pour water (to a height of about 2 cm) onto the calcium carbide in the Duran test tube (Fig. 9).
Close the Duran test tube by fitting on the bored stopper holding the gas tube (Fig. 10).
Fig. 9
Fig. 10
Put the gas tube in the plastic dish. After about 30seconds, lead the evolved gas into the two
water-filled, inverted test tubes until they are both filled with gas (Fig. 11). Close the test tubes
underwater with the stoppers and place them in the test tube rack.
Fig. 11
Move the apparatus away from the working area, position the test tubes well away from the
Bunsen burner.
Put a few drops of potassium permanganate solution in one of the test tubes containing
acetylene (only slightly lift the stopper) and close it again immediately (Fig. 12). Shake the tube
vigorously (Fig. 13).
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Fig. 12
Fig. 13
Hold the second test tube upside down, remove the stopper and hold the mouth of the tube
at the flame of the Bunsen burner (Fig. 14).
Fig. 14
Waste disposal
• Allow the calcium carbide to react completely (maybe add more water), then pour the
liquid into the acid and alkali waste container.
• Pour potassium permanganate solution also into the acid and alkali waste container.
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Results
Results
Note the observations you make.
During the reaction of calcium carbide:
On the addition of potassium permanganate solution:
While burning the collected gas:
During the reaction of calcium carbide:
The calcium carbide foams when water is added and a colourless gas is formed which
can be collected through the water in the dish. During the reaction the grey calcium
carbide changes its colour to white.
On the addition of potassium permanganate solution:
On shaking, the colour of the potassium permanganate solution changes to brown.
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While burning the collected gas:
The gas ignites with a quiet pop and burns with a yellow sooty flame.
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Evaluation
Evaluation
Question 1:
Draw conclusions from your observations and thereby answer the question in the header.
Calcium carbide reacts with water, forming a gaseous compound. Since this gas reacts
with the oxidizing agent potassium permanganate it cannot be an alkane, i.e. a
"saturated" compound, therefore it has to contain bonds other than unpolar single
bonds.
Question 2:
Formulate the equation for the reaction which took place.
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CaC2 + 2 H2O → C2H2 + Ca(OH)2
Question 3:
Which type of bond must be present, when the formed substance has the molecular formula
given in the reaction equation?
Since carbon is tetravalent, but only one hydrogen atom is attached to each carbon
atom, there must be a triple bond between the two carbon atoms.
Question 4:
Enter the observed properties of acetylene into the general data sheet, look up missing entries
in your text book to fill it in completely.
See "General data sheet".
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General data sheet
General data sheet
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Name of Acetylene
the
substance:
Chemical
nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
formula:
Colour:
nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
State of
nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
aggregation:
Melting
nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
point:
Boiling point: nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
Other
properties:
Occurrence/
preparation:
Use:
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General data sheet
Name of the substance:Acetylene
Chemical formula:
C2H2
Colour:
colourless
State of aggregation:
gaseous
Melting point:
-83.6 °C
Boiling point:
-81.8 °C
Other properties:
combustible, eplosive in certain mixtures with air,
burns with a sooty flame, reacts with potassium
permanganate turning it brown
Occurrence/
produced by cracking higher alkanes; formed during
preparation:
the reaction of calcium carbide with water or
hydrochloric acid
Use:
welding gas
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