Organic Chemistry

Testing for Gases Involved with Organic Chemistry

Purpose:  To explore tests of identifying oxygen, hydrogen, and carbon dioxide.

Materials:  Oxygen tank, Erlenmeyer Flask, pneumatic trough, wooden splint, magnesium ribbon, stopper with tubing, test tube, calcium carbonate, hydrochloric acid.

Safety:  Wear goggles and gloves.  Be in a well-ventilated area.

Procedure 1 – Oxygen:

·      Fill Erlenmeyer Flask completely with water

·      Invert flask under water, and without letting any air in, place the flask on top of the shelf in the pneumatic trough

·      Put latex tube (connected to oxygen tank) into the Erlenmeyer Flask filled with water

·      Open oxygen tank and let oxygen replace the water in the flask

·      Remove flask and quickly close with stopper

·      Light wooden splint and then blow it out

·      Open stopper and dip the wooden splint into the flask

Observations 1:  Once the oxygen tank was opened, a gas quickly replaced the water.  When the wooden splint was held inside the Erlenmeyer Flask, the tip reignited and burned brightly.  When the wooden splint was removed, the flame continued to burn.

 

Procedure 2 – Hydrogen:

·      Place magnesium ribbon in Erlenmeyer Flask

·      Fill another Erlenmeyer Flask with water and place on the shelf in the pneumatic trough

·      Pour hydrochloric acid into the Erlenmeyer Flask and close with stopper and latex tube

·      Put latex tube into upside-down flask in trough

·      Let gas replace water

·      Remove flask filled with gas and keep it facing down

·      Light wooden splint and hold it under the Erlenmeyer Flask turned slightly sideways

Observations 2:  The hydrochloric acid caused the magnesium ribbon to fizz and bubble vigorously.  Almost instantly, gas began to come out of the flask.  When the flame was put under the flask, there was a squeaky popping noise and the flame seemed to go out for a split second before igniting again.

Procedure 3 – Carbon Dioxide:

·      Put calcium carbonate (marble chips) in Erlenmeyer Flask

·      Fill another Erlenmeyer Flask with water and place upside down on shelf of trough

·      Pour hydrochloric acid in flask with calcium carbonate

·      Close with stopper and tube

·      Put tube in flask with water

·      Allow gas to replace water

·      Remove flask from water and quickly turn the opening up

·      Light wooden splint and dip into flask

Observations 3:  When the hydrochloric acid was poured onto the marble chips, the reaction wasn’t as vigorous as the magnesium ribbon, however it still bubbled and let off a gas.  When the wooden splint was dipped inside the flask, the flame immediately went out.

                                      Discussion

Because the wooden splint reignited in the oxygen, it showed that oxygen itself isn’t flammable, but it makes other substances in it extremely flammable.  This is why life cannot exist with more than 25% oxygen in the air.  Everyone would spontaneously combust.

The reason the Erlenmeyer Flask had to be held upside-down with the hydrogen gas was because this gas is less dense than air and, unless restricted, will float away.  The chemical formula for hydrogen is H2, and when it is lit, it combines with oxygen (O2). This forms H2O, which is water.  The popping noise is in fact water vapor rushing out. The reason the flame goes out for a bit is because the hydrogen uses the oxygen that the splint needs to stay lit.

Carbon dioxide sinks. That is why the flask had to be turned upwards.  Carbon dioxide is not explosive, but it also does not support combustion, therefore it is not possible for the flame to stay lit without oxygen.