preparation and properties of acetylene

PREPARATION

AND

PROPERTIES

OF

ACETYLENEEXPERIMENT 9

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

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)

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

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

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)

Orange flame that was produced

upon combustion of Acetylene gas.

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

Bromine Test

Before shaking After shaking

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

Von Baeyer’s Test

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

Formation of Silver acetylide

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

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

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

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

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

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

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

Alkynes Hydrocarbons w/ least one triple (CC)bond

Unsaturated

CnH2n-2

C-C triple bond high reactivity.

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.

Combustion the rapid reaction with oxygen (O2) and is

usually associated with flames or glowing

embers and is also called burning.

Substitution reactions are where one of the original atoms of the

compound have be replaced by another

element.

Flame color ranges from blue (almost complete,

hottest flame) to yellow to orange to red

(least complete, coolest flame)

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.

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)

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

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