Expt 032 -- Preparation and Properties of Oxygen

Oxygen (dioxygen) is prepared by the Fe²⁺ catalyzed decomposition of H₂O₂. The gas produced is collected by displacement of water. The gas is tested with a glowing splint and with glowing steel wool.

Background

The most important role of oxygen is to support combustion. In addition to fires and corrosion, the reactions of oxygen support nearly all forms of life. Many organisms have developed complex systems to obtain oxygen from their environment and to distribute that oxygen to cells in their bodies.

Safety

• Wear goggles and apron. Escaping dioxygen can cause mixtures of hydrogen peroxide solution to spray around the work area; wash hands thoroughly after the experiment. Avoid ingesting the chemicals.
• Hot glass and hot objects can cause burns. Hold a finger near a previously-heated object for several seconds before touching it to detect heat. Be careful when handling matches, splints, and especially hot steel wool. These can cause painful burns.

Procedure

1. Obtain a plastic transfer pipet, a 250-mL beaker, five 13 x 100-mm test tubes with stoppers, and a test tube rack or other test tube support (jar).
2. Fill the beaker three-fourths full with tap water. Fill four of the small test tubes completely with water. Hold the tip of your forefinger over the test tubes, one at a time, and invert then in the beaker of water. They should remain filled with water.

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3. Half-fill the fourth test with 3% H₂O₂. Add 6 drops 0.5 M Fe(NO₃)₃. Squeeze the transfer pipet to expel the air and draw up the solution to fill the bulb of the pipet about 80% full.

   !!!Click here to See Movie.

4. Hold the transfer piper with its tip pointing up alongside the beaker. Bend the tip down and place it under the water. A stream of bubbles is noticed. Wait for a few moments for the air to be flushed out by the gas being produced.
5. Lift one of the test tubes about 3 cm from the bottom of the beaker. Move the tip of the pipet so that a stream of gas bubbles is caught by the test tube. (Water will be displaced.)
6. When a tube is filled, set the pipet aside; hold a stopper under the tube in the beaker; stopper the tube; remove the filled tube and place it in a rack. Repeat for all four tubes.

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7. Remove a stoppered tube from the rack. Hold the tube about 6 inches from your nose, remove the stopper, and use your fingers to push (waft) some gas toward your nose. If it has a distinct odor, you'll get enough to detect by this procedure. Record the color and odor of the gas.
8. Use a match to light a wooden splint and allow it to burn. Blow out the splint leaving a glowing tip. Quickly remove the stopper from a second tube of gas and insert the splint. Note and record any changes.
9. Use a match to light a wooden splint and allow it to burn. Blow out the splint leaving a glowing tip. Quickly remove the stopper from the third tube of gas and insert the splint. Do not permit the splint to drop in the tube. Stopper the tube.

   !!!Click here to See Movie.

10. Remove the stopper and quickly add 1 mL limewater (saturated Ca(OH)₂) to the tube. Shake. Note and record any changes.

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    !!!Click here to See Picture.

11. Work with a partner. Roll a few strands of steel wool into a small cylinder. One partner grasps the cylinder of iron wool with a metal tweezers and heats for 12 seconds in a match flame. When the wool is red hot, the other partner uncorks and holds and oxygen tube while the first inserts the hot wool into the fourth tube of the gas. Note and record any changes.

    !!!Click here to See Movie.

    !!!Click here to See Movie.

    !!!Click here to See Picture.

12. Wash hands.

Questions

1. Summarize the properties of oxygen at room temperature.
2. Write a balanced equation for the production of oxygen from hydrogen peroxide.
3. Identify the role of Fe²⁺ in this reaction.
4. Write balanced equations for the combustion of carbon and iron.
5. Explain the role of the limewater. Write a balanced equation to describe any reaction that was observed.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

SmallScale 032 Preparation and Properties of Oxygen

Watch the movies. Note and record each chemical change from the movies. Carefully describe the appearance of substances before and after the chemical changes.

Answer the questions.

Curriculum-

Use when discussing elements, gases, oxygen, combustion, reduction, oxidation, redox,

Safety-

• Wear goggles and apron. Escaping dioxygen can cause mixtures of hydrogen peroxide solution to spray around the work area; wash hands thoroughly after the experiment. Avoid ingesting the chemicals.
• Hot glass and hot objects can cause burns. Hold a finger near a previously-heated object for several seconds before touching it to detect heat. Be careful when handling matches, splints, and especially hot steel wool. These can cause painful burns.

Time-

Teacher Preparation: 15 minutes

Class Time: 50 minutes

Materials-

• 5 mL of 3% hydrogen peroxide (commercial grade), H₂O₂. (6% H₂O₂ available from the hair products section of most drug stores works better.)
• 0.5 mL of 0.5 M Fe(NO₃)₃ (Dissolve 20 g iron(III) nitrate nonahydrate (Fe(NO₃)₃•9H₂O) 50 mL of water and 20 mL of 3 M HNO₃ dilute to make 100 mL solution.)
• 1 mL of limewater (place 1 g Ca(OH)₂ in 100 mL of water. Agitate frequently. After one day, filter. Store is a tightly sealed screw cap bottle away from carbon dioxide. Refilter before use if necessary.)
• steel wool
• wood splints
• matches
• metal tweezers
• test tube racks (or other supports)
• plastic transfer pipet
• 250-mL beaker
• 5 small test tubes 13 x 100 mm

Disposal-

All of the liquids may be disposed of at the sink while flushing with water. All of the solids (matches, splints, steel wool) may be discarded with ordinary solid waste.

Answers-

Q1. Summarize the properties of oxygen at room temperature.

A1. Oxygen is a colorless, odorless gas.

Q2. Write a balanced equation for the production of oxygen from hydrogen peroxide.

A2. H₂O₂ --> 2 H₂O + O₂

Q3. Identify the role of Fe²⁺ in this reaction.

A3. Since the H₂O₂ is purchased in solution from a store, it must be at least somewhat stable. (In fact, H₂O₂ has a rather short shelf life.) In order for the reaction to occur, a catalyst is used. Yeast and MnO₂ are effective catalysts. Fe²⁺ is one of the easiest catalysts to use.

Q4. Write balanced equations for the combustion of carbon and iron.

A4. C + O₂ --> CO₂

2 Fe + 3 O₂ --> Fe₂O₃

Q5. Explain the role of the limewater. Write a balanced equation to describe any reaction that was observed.

A5. Limewater tests for carbon dioxide. The white solid formed when limewater is exposed to CO₂ is CaCO₃.

Ca²⁺ + H₂O + CO₂ --> CaCO₃ + 2 H⁺

CoopLearn-

The heating of the iron wool requires that work be done in pairs.

Reference-

An early version of this experiment was developed by Dianne N. Epp, Lincoln, NE at the 1987 Dreyfus Woodrow Wilson summer program.

Key Words 1-

elements, gases, oxygen, combustion, reduction, oxidation, redox

Elements-

O Fe C