Preparation and properties of acetylene
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Transcript of Preparation and properties of acetylene
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PREPARATION
AND
PROPERTIES
OF
ACETYLENEEXPERIMENT 9
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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
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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)
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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
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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
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COMBUSTION2. 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)
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Orange flame that was produced
upon combustion of Acetylene gas.
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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
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Bromine Test
Before shaking After shaking
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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 pptEquation:
3 C2H2 + 8 KMnO4 + 4 H2O = 3 COOHCOOH + 8 MnO2 + 8 KOH
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Von Baeyer’s Test
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SUBSTITUTION REACTIONC. 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
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Formation of Silver acetylide
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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_article.htm
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Cont.2. Combustion of AcetyleneAcetylene 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/alkynes.html
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3. HalogenationAlkynes 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
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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
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4. OxidationEach 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
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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
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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
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Alkynes Hydrocarbons w/ least one triple (CC)bond
Unsaturated
CnH2n-2
C-C triple bond high reactivity.
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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.
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Combustion the rapid reaction with oxygen (O2) and is
usually associated with flames or glowing
embers and is also called burning.
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Substitution reactions are where one of the original atoms of the
compound have be replaced by another
element.
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Flame color ranges from blue (almost complete,
hottest flame) to yellow to orange to red
(least complete, coolest flame)
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From the experiment, we learned the truemeaning of cooperation. Through cooperation, wewere able to finish the experiment and obtain thecorrect results. This was due to the division of laborthat took place.
On the other hand, we realized howsignificant following the procedures were. Twice, weread those listed on the paper thoroughly. Then, theywere carried out carefully by the designated persons.
Furthermore, we had acquired newinformation. We have assimilated and built usefulinsights that we could utilize in the laboratory whenwe analyze body fluids and even blood samples.
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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 ammoniacalsilver nitrate (pale yellow-light brown ppt) and with ammoniacal copper(I) chloride solution (which gives an orange/red ppt)
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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
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MEMBERS:
Group 2
BSMLS 2D Cuasay, Jireh
Dimaano, Brian
Dimayuga, Mark
Boy
Garcia, Karissa
Gastardo, Jomia
Gonzales, Jemmuel
Lontoc, Shelah Mae
Organic
ChemistryDr. Aleli Bonifacio
Professor