organic chem

1. PREPARATION
AND
PROPERTIES
OF
ACETYLENE
EXPERIMENT 9

2. At the end of this activity, the students are
expected to have:
1. prepared acetylene gas by water
2. compared the properties of acetylene
with those of the paraffin and olefin series
compounds

3. A. Preparation of Acetylene
by hydrolysis of CaC2
 Acetylene (ethyne) is formed when water
reacts with calcium carbide, CaC2:
 Equation for the preparation
CaC2(s) + H2O(l) → Ca(OH)2(aq) + HC≡CH(g)

4. 1
•Place about 10 g of solid Calcium
carbide into a clean and dry distilling
flask.
•Insert the stem of a separatory funnel
into a cork that fits the mouth of the
flask.
2
•Adjust the funnel such the the stem is
near the Calcium carbide in the flask.
•Fill the funnel with water to half of its
capacity.
3
•Attach a rubber tubing to the stem of
the flask to serve as delivery tube.
•Fill 4 test tubes with acetylene gas.
•Collect a 5th tube but only to 1/15 of its
capacity.
water
CaC2

5. 1. Examine a tube of
acetylene gas.
Notice the color
and odor of the
odor of the gas.
Color: Colorless
Odor: garlic-like
B. Properties of Acetylene

6. COMBUSTION
2. Ignite a test tube of the gas and
immediately add 2.0 mL of clear lime water.
 What is the color of the flame? Yellow
 Equation:
2C2H2 + 5O2  4CO2 + 2H2O + heat
 What is formed after the addition of clear
lime water? White ppt
 Equation:
Ca(OH)2 (l) + CO2 (g)  CaCO3 (s) + H2O (l)

7. Orange flame that was produced
upon combustion of Acetylene gas.

8. 3. Add 1-2 drops of Bromine water to a test tube
containing acetylene gas. Cover and shake.
Describe what happened to the litmus paper.
Observation: Blue litmus paper remained blue.
Equation: C2H2(g) + Br2(aq) → CHBr=CHBr
HALOGENATION

9. Bromine Test
Before shaking After shaking

10. OXIDATION
4. Add 3.0 mL of dilute KMnO4 solution into a test
tube of acetylene. Stopper and shake.
Observation: A. Purple turned brown then colorless;
B. formation of brown ppt
Equation:
3 C2H2 + 8 KMnO4 + 4 H2O = 3 COOHCOOH + 8 MnO2 + 8 KOH

11. Von Baeyer’s Test

12. SUBSTITUTION REACTION
C. Formation of Silver acetylide
 What is the color of the ppt?
grayish to white
 Equation:
2AgNO3 (aq) + C2H2 (g)  Ag2C2 (s) + 2HNO3 (aq)
 What is produced upon ignition of ppt?
Orange flame
firecracker-like sound

13. Formation of Silver acetylide

14. 1. Properties of Acetylene
Color: colorless
Odor: offensive(decayed garlic)
The odor is entirely due to impurities in the coke and
lime; pure coke and pure lime will yield pure carbide.
Source:
http://panam1901.org/miscbuildings/acetylene/acetylene_articl
e.htm

15. Cont.
2. Combustion of Acetylene
Acetylene burns in air with a luminous, smoky
flame, (forming carbon dioxide and water).
2 C2H2 + 5 O2  4 CO2 + 2 H2O
The ethynes are highly dangerously explosives
when mixed with air or oxygen.
Source:
http://www.ucc.ie/academic/chem/dolchem/html/dict/alky
nes.html

16. 3. Halogenation
Alkynes undergo addition with halogen to give
tetra halo derivatives. Ethyne and bromine react
to form first 1, 2-dibromoethene and then 1, 1, 2, 2-
tetrabromoethane as follows:
C2H2(g) + Br2(aq) → CHBr=CHBr (g) (1, 2-dibromoethene)
CHBrCHBr + Br2(aq) → CHBr2CHBr2 (1,1, 2, 2-tetrabromoethane)
Source:http://www.juniata.edu/services/ScienceInMotion/chem/labs/gases/.../ethyne.do...%E2
%80%8E

17. Reaction with Bromine
Bromine reacts with C-C triple bonds by
addition across the double bond.
Disappearance of bromine color
(yellow/reddish/orange) within 10 seconds indicates
that it has reacted with a double or triple bond of a
hydrocarbon.
C2H2(g) + Br2(aq) → CHBr=CHBr
Source: http://www.chemhaven.org/che102/lab/CHE102_E21_S11.pdf
colorless yellow colorless

18. 4. Oxidation
Each hydrocarbon will also be reacted
with potassium permanganate, a strong
oxidizing agent. This test is commonly known as
the Baeyer test for unsaturation. The
carbon-carbon double and triple bonds are
oxidized to form alcohols or Diols.
Alkyne + KMnO4  diol + MnO2 (s)
colorless purple Colored ppt

19. Baeyer’s Test
 Evidence that the reaction has occurred
is the rapid disappearance (within a few
seconds) of the purple permanganate
color. The resulting reaction products will
generally be colored, typically a brown
solid, but varies with reaction condition
3 C2H2(acetylene) + 8 KMnO4 + 4 H2O 
3COOHCOOH + 8 MnO2 + 8 KOH
Source: http://www.chemhaven.org/che102/lab/CHE102_E21_S11.pdf

20. 5. Substitution Reaction of Acetylene
 Silver acetylide is formed when ethyne is passed into
an ammoniacal solution of silver nitrate.
 Equation:
2AgNO3 (aq) + C2H2 (g)  Ag2C2 (s) + 2HNO3 (aq)
Source: http://www.chemhaven.org/che102/lab/CHE102_E21_S11.pdf

21. Alkynes
 Hydrocarbons w/ least one triple (CC)bond
 Unsaturated
 CnH2n-2
 C-C triple bond high reactivity.

22. Calcium carbide
 dark brown or black;
 crystalline and brittle;
 S.g. of 2.22 to 2.26;
 may be heated to redness w/o change;
 will not burn except when heated in oxygen;
 If placed in water, or in any liquid containing
water, it will effervesce vigorously and liberate
acetylene gas.

23. Combustion
 the rapid reaction with oxygen (O2) and is
usually associated with flames or glowing
embers and is also called burning.

24. Substitution reactions
 are where one of the original atoms of the
compound have be replaced by another
element.

25. Flame color
 ranges from blue (almost complete,
hottest flame) to yellow to orange to red
(least complete, coolest flame)

26. From the experiment, we learned the true
meaning of cooperation. Through cooperation, we
were able to finish the experiment and obtain the
correct results. This was due to the division of labor
that took place.
On the other hand, we realized how
significant following the procedures were. Twice, we
read those listed on the paper thoroughly. Then, they
were carried out carefully by the designated persons.
Furthermore, we had acquired new
information. We have assimilated and built useful
insights that we could utilize in the laboratory when
we analyze body fluids and even blood samples.

27.  A luminous, very sooty flame is given if
alkynes are present.
 Reaction with bromine water and with
acidified potassium permanganate both
decolorize very slowly (unlike the alkenes)
 If terminal alkynes are being examined,
precipitates are obtained with ammoniacal
silver nitrate (pale yellow-light brown ppt) and
with ammoniacal copper(I) chloride solution
(which gives an orange/red ppt)

28. VIII. Application to Medical
Field
 The illuminating power of acetylene, in a
proper burner, is greater than that of any
other known gas; the flame is absolutely white
and of great brilliancy; its spectrum closely
approximates that of sunlight, and
consequently it shows the same colors as
daylight. It is strongly actinic and well
adapted for photography. It neither heats nor
pollutes the air so much as coal-gas.
Source:
http://panam1901.org/miscbuildings/acetylene
/acetylene_article.htm

29. MEMBERS:
Group 2
BSMLS 2D
 Cuasay, Jireh
 Dimaano, Brian
 Dimayuga, Mark
Boy
 Garcia, Karissa
 Gastardo, Jomia
 Gonzales, Jemmuel
 Lontoc, Shelah Mae
Organic
Chemistry
Dr. Aleli Bonifacio
Professor