Countertop Chemistry Experiment 7
Production of Oxygen

This experiment allows the students to generate a gas, oxygen, and test some of its properties.

Materials	Substitutions
hydrogen peroxide 3%
yeast
125 mL erlenmeyer	small jar
stopper	lid
wood splints	toothpicks
candle and matches

Procedure

1. Pour approximately 100 mL of 3% hydrogen peroxide into the flask.
2. Light the candle in preparation for studying the gas.
3. Add 2 tsps. of yeast to the H₂O₂ and cover loosely with the lid. Bubbles of gas should begin to form.
4. Light a splint and allow it to burn for a few seconds. Extinguish the flame so that the splint is glowing.
5. Immediately, remove the lid and insert the glowing splint into the neck of the jar. Note the result. Replace the lid and collect more gas.
6. Repeat step #4 to retest the gas.

Questions

1. Write the equation for the reaction that occurred in the above experiment.
2. What happened when the glowing splint was placed near the opening of the glass jar?
3. Why must the container be closed during the experiment?
4. List any precautions that should be used if high concentrations of oxygen are present (e.g. the use of oxygen for hospital patients).

Teacher's Notes

In 1774, Joseph Priestly first prepared oxygen. He accomplished it by focusing the sun’s rays on mercury (II) oxide, producing liquid mercury and a gas. Priestly discovered that the gas made a candle burn more brightly. Antoine Lavoisier determined the role that oxygen plays in combustion and respiration.

Nearly all commercial oxygen is obtained from the separation of the elements in air. This method is chosen because of the abundance of the starting material and the ease of the process of isolating pure oxygen. In this experiment, oxygen is produced from the decomposition of hydrogen peroxide into oxygen and water.

YOUR HYDROGEN PEROXIDE MUST BE FRESH. H₂O₂ loses oxygen when it is exposed to heat or light. Liver can also be used as a catalyst for an interesting twist. When we use peroxide to sterilize a wound, the peroxide decomposes to release oxygen. Both enzymes (e.g. in the liver) and metal ions can catalyze this reaction

1. 2H₂O₂ (aq) ^{__ yeast __} > 2H₂O (l) + O₂ (g)
   Yeast is a catalyst for this decomposition and, therefore, can be written over the reaction arrow.
2. The splint will reignite when placed in the flask because oxygen supports combustion. Combustion is the chemical combination of a substance with oxygen. An oxide is one of the products.
3. The container must be stoppered (or closed in some manner) to avoid loss of the oxygen. Without the stopper, the oxygen would escape into the room.
4. The atmosphere is composed of 21% oxygen. If this percentage were increased, any combustion would proceed at a greater rate.

Safety Precautions

1. The flask may become hot due to the exothermic nature of the reaction. Use care.
2. Oxygen is a component of combustion reactions. No open flames or sparks should be near the gas production or storage area.

Disposal

All solid material can be placed into a trash container. All solutions may be poured into the sink.

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