E3 Acetylene

Experiment #3 Acetylene and chemical properties of the alkynes
Initial Questions:
1. What is acetylene?
2. What are the ways of synthesizing acetylene?
3. Why do you need to synthesize acetylene in the lab?
4. What is reactivity of alkynes based on? What is the most common mechanism?
5. Silver carbide and copper(I) acetylide are very explosive. What safety measures should
you take?
Materials: Reagents:
1 distillation flask of 500 ml calcium carbide

1 matraz de destilación de 500 ml carburo de calico
1 separating funnel of 250 ml potassium permanganate
1 embudo de separación de 250 permanganato de potasio
ml Sodium bicarbonate
3 test tubes of 18 x150mm with screw cap Bicarbonato de Sodio
3 tubos de ensaye con tapa
2 100 ml beakers bromine
1 hose
1 manguera bromo
1 clip for crucible
1 Pinza para crisol Carbon tetrachloride
5 pipettes of 5 ml tetracloruro de carbono
5 pipetas de 5 mL
Silver Nitrate
1 rack
nitrato de plata
1 gradilla
1 bracket
Nitric acid
1 Soporte
Ac. Nítrico
1 burner
1 Mechero Copper(II) sulfate pentahydrate
1 iron ring Sulfato cuproso (pentahidratado)
1 anillo de hierro
1 Cuba hydropneumatic Ammonium solution
1 asa calibrated
spatula
Experimental Procedure:
Glassware set up. The main flask topped with a rubber stopper with two holes, one for the separating
funnel the other for the glass tubing. A rubber tube is connected to the side of the flask or the glass
tubing and goes under water into upside down glass tube. The acetylene is collected by displacement of
the water contained in the tubes.
Place about 4 g of carbide of calcium into the flask. 10 ml of distilled water are placed in the separating
funnel. Open the valve of the funnel leaving slowly dripping water onto calcium carbide. At first air will
be pushed through the system. When acetylene is detected collects the acetylene in 3 test tubes by
water displacement. When collection of the gas in tubes is completed run the gas through two solutions
for the following reactions.
Chemical properties:
Reaction #1. Silver Nitrate. Use end of the rubber tube to pass the gas through test tube filled with
ammoniacal silver nitrate to observe the formation of a precipitate. To prepare silver nitrate solution,
take about 0.2 g of AgNO3 dissolve in 20ml water. Next, add 1ml of nitric acid. Place the solution in a
bicker and run the acetylene. What happens in the solution?
2AgNO3 + C2H2 → ????
Collect some of the precipitate and place it in direct fire. What do you observe?
Reaction #2. Copper(I) sulfide. Use end of the rubber tube to pass the gas through test tube filled with
ammoniacal copper sulfide to observe the formation of a precipitate. To prepare cuprous ammonium
sulfide solution take about 0.5 g of CuSO4 dissolve it in aqueous ammonium. Next, run the acetylene gas
through the solution in the bicker. What happens in the solution?
2CuSO4 + C2H2 + 2(NH3•H2O) → ????
Collect some of the precipitate and place it in direct fire. What do you observe?
Test Tube #1. Potassium Permanganate. Use or prepare a very dilute aqueous solution of potassium
permanganate. Pour 1 ml of the KMnO4 into test tube #1 place the cap back on. Shake the solution
vigorously. The pink color of permanganate will disappear, and tiny bubbles will be observed in the
solution.
Ethyne and permanganate react with cleavage on the carbon-carbon triple bond and formation of the
formate ion and the carbonate ion. If the conditions are neutral or acidic, the formate ion is
converted to formic acid and the carbonate ion forms carbon dioxide
What is the reaction?
3 C2H2(g) + 8 MnO4-(aq)+ 8 H+(aq) → ?????
Next, add a 1% solution of sodium bicarbonate. What happened? What reaction occurred? What did you
see?
NaHCO3 + … → ???
Test Tube #2. Bromination. Added to the second test tube 2 ml of an aqueous solution of bromine.
Ethyne and bromine react to form first 1, 2-dibromoethene and then 1, 1, 2, 2-tetrabromoethane. Write
the reactions and explain how easy the reaction is.
C2H2(g) + Br2 → ???
Test Tube #3. Combustion. Use test tube #3 to ignite the gas inside. Move a ignited wooden stick to the
edge of the test tube. What do you observe? What is the reaction?

E3 Acetylene

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Experiment #3 Acetylene and chemical properties of the alkynes

1 distillation flask of 500 ml calcium carbide

2AgNO3 + C2H2 → ????

2CuSO4 + C2H2 + 2(NH3•H2O) → ????

What is the reaction?

3 C2H2(g) + 8 MnO4-(aq)+ 8 H+(aq) → ?????

C2H2(g) + Br2 → ???

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