Kitchen Chemistry Experiment 7
Production of Oxygen

How do you produce a gas? What are some of the properties of oxygen? How do you test for oxygen?

 

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

Procedure

 

1. Pour 100-150 mL of 3% hydrogen peroxide into a jar
2. Light a candle a prepare to test for a gas.
3. Add 2 teaspoons of yeast to the H2O2 and cover loosely with the lid. Bubbles of gas should begin to form momentarily.
4. Light a splint and allow it to burn for a few seconds. Shake out the flame so that the splint is glowing.
5. Immediately, remove the lid and insert the glowing splint into the neck of the jar. What happens? Replace the lid to collect more gas.
6. Repeat step #4 and retest for the gas.

 

Extensions

1. Write the equation for the reaction occuring in the above experiment.
2. What happened when the glowing splint or toothpick was placed near the opening of the glass jar?
3. Why must the lid be kept on the jar for this experiment?
4. Why is smoking prohibites in hospital rooms where a patient is receiving oxygen?

 

 

Teacher's Notes

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

Nearly all commercial oxygen is obtained from air or water because of their abundance, availability, cheapness and ease of preparation. However, 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 sterlize a wound, the iron in our blood acts as the catalyst to cause the release of the oxygen. Iron in the liver acts the same way. Chemists almost always use Manganese, iron's nearest neighbor on the periodic table, to do this demonstration.

 

1. 2H2O2 (aq) ^{__ yeast __} > 2H2O (l) + O2 (g)
2. The toothpick or splint will reignite because oxygen supports combustion. Combustion is the chemical combination of a substance with oxygen. An oxide is the product.
3. Oxygen is lighter than air so it would escape if a lid or stopper were not used.
4. Our air is only 21% oxygen. Imagine how dangerous it would be to have an open flame near 100% oxygen!!

 

Safety Precautions

1. If you are using glass bottles or jars, the containers should be wrapped with a cloth. This reaction is exothermic!!
2. Oxygen gas is flammable! Do not have open flames or sparks near gas production or storage area.