Materials Included In Kit

Additional Materials Required

Prelab Preparation

Prepare the “Blue Bottle” solution fresh on the day of the lab. Chemicals are provided to make 500 mL of “Blue Bottle” solution, roughly 30 mL per group. In a 500-mL flask, mix together all 250 mL of the dextrose solution with all 250 mL of the potassium hydroxide solution. Add 15–20 drops of the methylene blue indicator solution. Label the flask as the “Blue Bottle” solution. (Note: If less “Blue Bottle” solution is needed for the class, use proportionally less of each chemical. Once mixed, the solution is not stable for more than the day.)

Safety Precautions

Gases in the syringe may be under pressure and could spray liquid chemicals. Follow the instructions and only use the quantities suggested. Hydrogen peroxide solution is an oxidizer and a skin and eye irritant. The “Blue Bottle” solution contains materials that are slightly corrosive to tissues. Use care when using matches. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Excess O₂ can be released into the air. Excess reagents can be rinsed down the drain with plenty of water according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• Enough materials are provided for a class of 30 students working in pairs or 15 groups of students. All parts of the lab can be completed in a standard 50-minute lab period if Post-Lab Questions are completed either outside of class or on day 2.
• An excess of potassium iodide and 6% hydrogen peroxide solution are provided in case students need to make extra oxygen to repeat some of the tests.
• The oxygen gas that is generated can be stored in the sealed syringe for extended periods of time.
• Demonstrate the procedure for washing oxygen. Washing the gas removes excess reagents from the syringe, which could affect any of the experiments involving oxygen.
• Supply a waste beaker at each lab table for the wastewater from the washings.
• After the Part 1 generation of the oxygen gas procedure, students may wonder why the solution in the syringe is yellow. This color is due to iodine, I₂, which is also formed as a byproduct of the reaction. The iodide ion is oxidized to iodine by hydrogen peroxide.
• For Part 2, you may wish to provide students with the balanced equation for the reaction of the burning of one of the volatile components of wax as follows: C₂₅H₅₂(g) + 38O₂(g) → 25CO₂(g) + 26H₂O(g). The object of Part 2 is to show that oxygen is needed for combustion reactions and that one of the major products of combustion is carbon dioxide.
• The limewater provided to students for Part 2 should be clear. If the stock limewater is agitated and the solution turns cloudy, allow the solution to settle. Decant the solution by pouring out the liquid above the solid and using the clear liquid for the test. The solution may need to sit for an entire day in order to allow settling to occur.
• Students should obtain the limewater just prior to performing Part 2. If allowed to sit out on the lab bench, the limewater will become cloudy within 15 minutes from the carbon dioxide in the air.
• The “Blue Bottle” experiment in Part 4 is an oxidation–reduction reaction. The conversion of “colorless” methylene blue to “blue” methylene blue occurs when there is oxygen in the solution
  {11921_Tips_Reaction_1}
  Upon shaking, which adds oxygen to the solution, the solution turns from colorless to blue as methylene blue is oxidized and O₂ is reduced. Shaking the syringe causes more O₂(g) to dissolve in the water and become O₂(aq). Upon standing undisturbed, dextrose reduces the blue methylene blue back to the colorless form
  {11921_Tips_Reaction_2}
  The oxidation–reduction process can be repeated dozens of times.
• Use the “Blue Bottle” experiment to review Le Chatelier’s principle. Adding O₂ to the solution by shaking the syringe causes the equilibrium to shift to the right (blue color is seen). If the syringe sits undisturbed, dextrose reduces the methylene blue to a colorless form. The equilibrium shifts to the left (colorless solution is seen).
• For additional interesting oxidation–reduction demonstrations, the following chemical demonstration kits are available from Flinn: Feeling Blue Kit (Catalog No. AP8653), Stop-’N-Go Light Kit (Catalog No. AP2083) and Vanishing Valentine Kit (Catalog No. AP5929).

Sample Data

Answers to Questions

Part 1. Preparation of Oxygen Gas

1. Write the balanced chemical equation for the reaction occurring in the syringe.
   
   {11921_Answers_Equation_1}
2. How many moles of O₂ gas can be expected if 5 mL of 6% H₂O₂ are used in the reaction? (Hint: Density of 6% H₂O₂ is 1.0 g/mL)
   5 mL x 1 g/mL = 5 g x 0.06 = 0.30 g H₂O₂ 
   0.30 g H₂O₂  x 1 mol/34.02 g = 0.0088 moles of H₂O₂
   From the balanced equation, ½ mole of O₂ is produced for each mole of H₂O₂.
   Therefore, 0.0044 moles of O₂ gas are expected.
3. Referring to Question 2, what volume in mL of oxygen is expected? (Hint: Use the Ideal Gas Law and assume P = 1.00 atm, T = 298 K, and R = 0.0821 L•atm/mol•K).
   V = nRT/P = (0.0044 mol)(0.0821 L•atm/mol•K)(298 K) / 1.00 atm 
   V = 0.108 L or 108 mL of O₂ gas are expected.

Part 2. Oxygen and Combustion

4. What chemical property of oxygen is illustrated in both parts of this experiment?
   Oxygen is combustible and is needed for combustion reactions.
5. What type of reaction is occurring in both parts of this experiment?
   This is a combustion reaction between one of the components of wax and oxygen. 
   C₂₅H₅₂(g) + 38O₂(g) → 25CO₂(g) + 26H₂O(g) 
6. What happened to the candle flame in Part B? Explain your observations.
   The flame goes out in Part B after all the oxygen in the syringe reacts with the volitile hydrocarbons from the wax to produce carbon dioxide and water.
7. What gases are replacing the oxygen in the syringe in Part B? How do you know?
   Carbon dioxide and water are replacing the oxygen in the syringe.
8. Write the reaction between the gas produced in Part B and limewater. 
   CO₂(g) + Ca(OH)₂(aq) → CaCO₃(s) + H₂O(l)

Part 3. Steel Wool and Oxygen

9. Does the steel wool burn faster in the air or in pure oxygen? Explain why.
   Reaction rates depend on the concentration of the reactants; thus, increasing the concentration of a reactant will make the reaction go faster. In the experiment, oxygen reacts with the iron in the steel wool. The reaction is much faster in pure oxygen than it is in air because there are many more oxygen molecules reacting with the iron.
10. (a) Predict what would happen if you were to use coarse steel wool instead of the fine steel wool you used in the experiment. (b) Predict what would happen if you were to use iron powder instead of steel wool.
    Reaction rates are also dependent on the particle size of the reactants. The reaction will go faster using smaller-sized iron particles. The coarse steel wool has much larger iron fibers and would react very slowly while the powdered iron has the smallest particles. The smallest-sized particles would mean greater exposure of the reactants to each other, that is, the greatest surface area for reactants to be in contact with each other and a faster reaction.
11. What are the two reactants in the experiment? If the product is Fe₂O₃, write the balanced equation for the reaction.
    The reactants are iron and oxygen. 4Fe(s) + 3O₂(g) → 2Fe₂O₃(s)

Part 4. The Blue Bottle Experiment in a Syringe!

12. What is the purpose of shaking the syringe containing the oxygen and the Blue Bottle solution?
    Shaking the syringe causes more of the oxygen gas to dissolve in the aqueous phase. The concentration of oxygen is increased.
13. Which direction will the equilibrium position shift when oxygen gas is added to the solution in the syringe?
    
    {11921_Answers_Reaction_3}
14. Does O₂ gas cause the solution to become blue or colorless? What type of reaction is occurring?
    Oxygen causes the oxidation of the “colorless” methylene blue to “blue” methylene blue. In the meantime, oxygen is reduced to hydrogen. This is an oxidation–reduction reaction where the indicator methylene blue is colorless in its reduced form and blue in its oxidized form.

Discussion

Optional Demonstration

Oxygen and a Flame

1. Prepare a third syringeful of O₂ gas by repeating the procedure from Part 1. This experiment requires 60 mL of O₂ gas.
2. Light a Bunsen burner for use in step 4.
3. Remove the syringe cap and quickly attach a piece of latex tubing to the syringe.
4. Position the open end of the latex tubing into the burner’s air intake slot. The end of the tubing should be in the middle of the intake slot so that the O₂ will join the gas stream when discharged.
5. Slowly depress the plunger to discharge the oxygen into the slot. When the plunger is completely depressed, turn off the Bunsen burner.
6. Record your observations on the data sheet.
7. Observe that the inner cone of the flame becomes smaller and a little wider; the flame is hotter and brighter.

References

Special thanks to Bruce Mattson, Creighton University, Omaha, Nebraska for the microscale gas generation and testing procedures used in this kit. For more experiments on microscale gas generation and testing, please purchase Chemistry of Gases: A Microscale Approach, AP4849, from Flinn Scientific, Inc.

Mattson, Bruce; Anderson, Michael; Schwennsen, Cece Chemistry of Gases: A Microscale Approach, Flinn Scientific: Batavia, IL; Chapter 5.

Introduction

Oxygen! We need it to breathe and to survive. Learn how O₂ is prepared and observe some interesting properties of oxygen.

Concepts

• Gases
• Preparation of oxygen gas
• Properties of oxygen gas

Background

Oxygen is quite familiar because it is the second largest component of the Earth’s atmosphere (21%). It also occurs as the allotrope O₃, called ozone, in the atmosphere. It represents 89% of the mass of a water molecule so it is a key building block of the Earth’s water supply. Much of the Earth’s lithosphere (rocks, solid parts of the crust) is composed of silicates and other oxides. Taken together, over 46% of the mass of the lithosphere is oxygen. Because the Earth’s surface is bathed in oxygen, it may seem that O₂ is relatively non-reactive. In fact, oxygen is the second most reactive of all elements; only fluorine, F₂, is more reactive. Oxygen reacts directly with most of the other elements. The exception being the halogens, noble gases and a few non-reactive metals such as gold. Reactions with oxygen are often slow, such as the oxidation of iron. On a geological time scale, these reactions are fast enough so that there is very little native iron present in the Earth’s crust. The rate of the reaction of iron with oxygen increases dramatically as the temperature is increased.

Oxygen is a colorless, odorless and tasteless gas at room temperature and pressure. It can be condensed to a pale blue liquid by cooling to –183 °C (90 K) at a pressure of one atmosphere. Liquid oxygen, often called LOX, reacts explosively with organic substances and must be handled with great care. At 20 °C oxygen dissolves in water to the extent of 30.8 cm3 per liter. It is even more soluble in numerous non-aqueous solvents.

Photosynthesis accounts for virtually all of the oxygen present in the Earth’s atmosphere. Water and carbon dioxide are converted by chloroplasts to oxygen and plant carbohydrates, such as glucose.

Oxygen can be made using several different routes, but this lab will use the catalytic disproportionation of hydrogen peroxide.
 
Oxygen supports combustion. This familiar phrase has important chemical significance. A combustion reaction is one in which a substance, often an organic hydrocarbon, combines with oxygen to produce carbon dioxide and water. These reactions are special forms of oxidation–reduction reactions in which so much heat is released that flames are produced. When methane burns in a Bunsen burner, for example, the reaction is
 
Even metals are known to “burn” in air. Finely divided metal particles will undergo a combustion reaction with the oxygen in air to produce an oxide of the metal. For example, zinc powder will “burn” in the flame of a Bunsen burner to form zinc oxide.


In this lab, oxygen will be generated by combining a potassium iodide (KI) solid catalyst with 6% hydrogen peroxide solution (H₂O₂) according to the following equation. This reaction is convenient and does not require heat. 

Materials

Safety Precautions

Gases in the syringe may be under pressure and could spray liquid chemicals. Follow the instructions and only use the quantities suggested. Hydrogen peroxide solution is an oxidizer and a skin and eye irritant. The “blue bottle” solution contains materials that are slightly corrosive to tissues. Use care when using matches. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

(Note: The reaction proceeds very slowly, taking a minute or more to generate the gas. Shaking the syringe and gently pulling on the plunger will speed the process.)

Part 1. Preparation of Oxygen Gas

1. Inspect the syringe making certain that the plunger moves freely in the syringe, and that both the plunger seal and syringe are free from cracks. If the plunger moves with difficulty, it may be necessary to lubricate the rubber seal with a thin film of silicone oil. (Lubricate only the edge that makes contact with the inner barrel wall.)
2. Measure out 0.10 g of KI powder and place it into a plastic vial cap. Avoid getting any chemical on the sides of the vial cap.
3. Remove the plunger from the syringe barrel. Hold your finger over the tip of the syringe. Fill syringe completely with tap water. The water should be even with the top of the syringe.
4. Carefully place the vial cap containing the solid reagent on the surface of the water face up so that it floats.
5. Remove your finger from the syringe opening and allow the water to flow out of the syringe into a flask, a beaker, or into the sink. As the water level decreases, the vial cap will be lowered to the bottom of the syringe. When successfully completed, the cap should rest upright on the bottom of the syringe with all of the reagent still in the cap. If the vial cap tips over and the solid spills out, clean out the syringe and start over.
   {11921_Procedure_Table_2}
6. Carefully replace the plunger while maintaining the syringe in a vertical position. Gently push the plunger in as far as it will go. It will anchor the vial cap into the depression at the base of the syringe. (Note: There is a point just after the plunger’s rubber diaphragm enters the barrel where there will be resistance. Gently, but firmly, push the plunger past this point.)
7. Pour about 10 mL of 6% H₂O₂ into a small beaker.
8. Draw about 5 mL of 6% H₂O₂ from the beaker into the syringe. Be careful that the vial cap does not tip over since it will cause the reaction to begin prematurely.
9. Secure the latex syringe cap on the tip of the syringe by setting the syringe cap on the counter and quickly pushing the syringe into the cap. The latex syringe cap will push on.
   {11921_Procedure_Table_3}
10. Read step 11 now to understand how to stop the reaction. Do this before going on. Perform the reaction by shaking the syringe vigorously. The reagents will mix causing the reaction to proceed. The plunger will move outward as it is displaced by the gas. Do not leave syringe unattended. Although many reactions are rapid, this reaction proceeds slowly and there will be a temptation to set the syringe aside while the reaction continues.
11. The next three steps (11, 12 and 13) should be performed quickly to minimize any loss of gas. When the reaction is completed or the volume of gas is about 50–60 mL, tip the syringe up to stop the reaction and remove the syringe cap. If the reaction is occurring too rapidly, or generating more than 50–60 mL of gas, stop gas collection by using the tilt, twist and release procedure. Tilt the syringe so the tip is pointing upward but away from anyone. Twist off the syringe cap with a slight twist, and release the pressure.
12. Hold the syringe with the tip pointing downward. Discharge the liquid reagents into the sink or a beaker. Use caution during this step so that none of the gas is discharged.
13. Secure the latex syringe cap back on the tip of the syringe.

Washing Procedure

After preparing the O₂ gas, it is necessary to wash the inside of the syringe in order to remove excess reagents. Follow the steps below and repeat if necesssary. This washing procedure, if done properly, will not affect the gas. All traces of the reactants should be washed away before proceeding.

1. Remove the syringe cap with the tip of the syringe pointing up. (A)
2. Draw a few mL of water into the syringe. (B)
3. Recap the syringe. (C)
4. Shake the syringe to wash the inside surfaces. (D)
5. Remove the syringe cap again. (A)
6. Discharge the water only into the sink or a beaker. (Note: Do not depress the plunger fully or the gas will be lost.) (E)
7. Recap the syringe. (C)

Part 2. Oxygen and Combustion

1. Use about 60 mL of O₂ gas from Part 1 for this part of the experiment.
2. Place a candle in a one-hole stopper to stand it up. Light the candle and set it aside.
3. Clamp the syringe firmly in a vertical position with the plunger-end up and the sealed tip pointing downward. Carefully remove the plunger from the syringe.
4. Use the candle to light the wood splint.
5. Blow the flaming splint out. Immediately plunge the splint into the O₂-filled syringe while the splint is still glowing red. Lift the splint slightly out and again plunge the splint into the syringe.
   {11921_Procedure_Table_6}
6. Record your observations on the data sheet.
7. Prepare another syringeful of O₂ gas by repeating the procedure from Part 1. About 60 mL of O₂ is needed for this part of the experiment.
8. Clamp the syringe containing O₂ gas firmly in a vertical position. This time the plunger-end should be in the down position with the sealed tip pointing upward.
9. Remove the plunger from the syringe. Immediately raise the lit candle into the O₂-filled syringe. Wait for the flame to extinguish before removing the candle.
10. Record your observations on the data sheet.
    {11921_Procedure_Table_7}
11. Re-install the plunger into the syringe barrel just until the rubber seal is at the 60-mL mark. (Note: Do not refill the syringe with O₂. This is a test to determine what gas is currently in the syringe.)
12. Fill a small beaker with 15 mL of fresh limewater.
13. Remove the syringe cap and quickly attach a piece of latex tubing to the syringe.
14. Bubble all of the gas from the syringe through the limewater solution.
15. Record your observations on the data sheet.

Part 3. Steel Wool and Oxygen

1. Prepare a third syringeful of O₂ gas by repeating the procedure from Part 1. This experiment requires 60 mL of O₂ gas.
2. Light a Bunsen burner and set aside for use in step 6.
3. Make a small ball of steel wool by gently pulling apart the steel wool fibers.
4. Remove the latex cap from the syringe of O₂ gas.
   {11921_Procedure_Table_9}
5. Hold the steel wool securely with forceps.
6. Light the steel wool with the burner until it is glowing red. Remove the steel wool from the flame and turn off the Bunsen burner.
7. Slowly depress the plunger of the syringe discharging the oxygen onto the glowing steel wool.
8. Record your observations on the data sheet.

Part 4. The Blue Bottle Experiment in a Syringe!

1. Prepare another syringeful of O₂ gas by repeating the procedure from Part 1. This time, only prepare about 40 mL of O₂ gas.
2. Pour 30 mL of “Blue Bottle” Solution into a 100-mL beaker. Your instructor will provide this solution.
3. Remove the latex cap from the syringe and draw 25 mL of the “Blue Bottle” solution into the syringe (that has about 40 mL of O₂).
4. Securely replace the syringe cap on the tip of the syringe.
   {11921_Procedure_Table_11}
5. Shake the syringe once and the solution should turn blue. Observe the syringe over the next several minutes. It should begin to fade, and become colorless within 5–10 minutes.
6. Record your observations on the data sheet.
7. Shake the syringe again and observe the syringe over the next several minutes. Whenever the color fades, shake the syringe again. What do you think is the purpose of the shaking?
8. Record your observations on the data sheet.

Student Worksheet PDF

11921_Student1.pdf