Materials Included In Kit

Additional Materials Required

Safety Precautions

Gases in the syringe may be under pressure and could spray liquid chemicals. Follow the instructions and only use the quantities suggested. Ammonium hydroxide and hydrochloric acid solutions are toxic by inhalation, ingestion and are corrosive to all body tissues. Ammonia fumes can burn nasal membranes; always handle ammonia solutions in an operating fume hood. Use care when using matches. Sodium hydroxide is corrosive to all body tissues; handle with care. 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 CO₂ 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. Have students complete post-lab questions either outside of class or on Day 2. Or, if desired, have students perform the procedure and post-lab questions for Parts 1, 2 and 3 on Day 1 and Parts 1, 4 and 5 on Day 2.
• An excess of sodium bicarbonate and 1 M hydrochloric acid solution are provided in the kit in case students need to make extra carbon dioxide to repeat some of the tests.
• The carbon dioxide gas that is generated can be stored in the sealed syringe for extended periods of time.
• The limewater provided to students in 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.
• If time permits, allow students the opportunity to test their ideas concerning Post-Lab Questions 19 and 20.
• Demonstrate the procedure for washing carbon dioxide. Washing the gas removes HCl from the syringe, which could affect any of the experiments involving carbon dioxide.
• Supply a waste beaker at each lab table for the wastewater from the washings.

Sample Data

Answers to Questions

Part 1. Preparation of Carbon Dioxide Gas

1. Write the balanced chemical equation for the reaction occurring in the syringe.
   HCl(aq) + NaHCO₃(s) → NaCl(aq) + H₂O(l) + CO₂(g)
2. When using 0.22 g of NaHCO₃ and 5.0 mL of 1.0 M HCl, which reactant is the limiting reactant? Show all work.
   The limiting reactant is NaHCO₃. 
   0.22 g NaHCO₃ x mol/84.01 g = 0.0026 mol NaHCO₃
   1.0 mol/L HCl x 0.0050 L = 0.0050 mol HCl
3. What type of reaction is occurring in the syringe—oxidation–reduction, acid/base or precipitation?
   This is an acid/base reaction since HCl is an acid and NaHCO₃ is a base.

Part 2. Classic Test for Carbon Dioxide

4. Write the balanced chemical equation for the reaction occurring between the carbon dioxide and the limewater [a saturated solution of calcium hydroxide, Ca(OH)₂].
   CO₂(g) + Ca(OH)₂(aq) → CaCO₃(s) + H₂O(l)
5. What was observed after adding the carbon dioxide gas to the limewater?
   A white precipitate is seen after CO₂ gas is bubbled into the limewater.

Part 3. Carbon Dioxide and pH

6. Write the chemical equation for the reaction occurring between the carbon dioxide and the ammonia gas.
   
   {11914_Answers_Equation_1}
7. What is the pH of the distilled or deionized water in the laboratory? Explain why it has this pH.
   Distilled water is slightly acidic and the pH is around 6.0 (yellow to light green) with universal indicator. This is because the carbon dioxide in the air dissolves slightly in the water.
8. Is ammonia gas soluble in water? Explain.
   After adding ammonia vapors to the water, students should see a rapid color change in the indicator to a blue-violet color. This should be evidence that ammonia is soluble in water.
9. From lab observations, is ammonia an acid or a base? Is carbon dioxide an acid or a base? Explain.
   The indicator color will be blue or violet after ammonia is added, showing that ammonia is a base. The pH will be above 8. After adding carbon dioxide, the indicator color will return to the yellow and orange colors, showing that carbon dioxide is an acid. The pH will be below 6.
10. What changes occurred to the indicator in this experiment? What is the cause of the changes?
    Indicators are organic molecules or dyes that change color when the pH is changed. In the experiment, the indicator changed colors when ammonia and carbon dioxide were added. When the pH changed, the color of the indicator changed.
11. Explain how indicators can be useful to scientists.
    Indicators are useful to chemists to determine whether a solution is acidic or basic. Universal indicator can tell a chemist the approximate pH of a solution.

Part 4. Reaction of Carbon Dioxide and Sodium Hydroxide

12. Write the balanced chemical equation for the reaction that occurred in the syringe.
    CO₂(g) + NaOH(aq) → Na₂CO₃(s) + H₂O(l)
13. Suggest an explanation for what was observed in this experiment.
    The carbon dioxide gas in the syringe reacted with the aqueous sodium hydroxide. When carbon dioxide goes from the gas phase to the aqueous phase, the pressure inside the syringe decreases causing the plunger to be drawn inward.
14. What change in pressure was observed? Explain.
    The pressure in the syringe decreased. Gas pressure is a result of gas molecules colliding with the container walls. In this experiment, the number of carbon dioxide gas molecules decreased because they reacted with the sodium hydroxide. This caused the pressure and volume of CO₂(g) inside the syringe to rapidly decrease.
15. Solutions of bases such as sodium hydroxide or calcium hydroxide are not stable if they sit in the air for an extended period of time. Based on your experiments with CO₂(g), suggest a reason for this.
    Solutions of sodium hydroxide or other bases are not stable if they sit in the air because they will react with the carbon dioxide in the air.

Part 5. Does Carbon Dioxide Support Combustion?

16. What happened to the burning candle? Could this gas be used as a fire extinguisher?
    The flame went out when exposed to the carbon dioxide. Carbon dioxide does not support combustion and is ideal for use in a fire extinguisher as it quickly extinguishes flames.
17. Why is the syringe held upright in the experiment? Will the carbon dioxide quickly escape?
    Carbon dioxide is more dense than air and the syringe should be placed with the barrel opening in an upright direction. If the syringe were held upside down, the carbon dioxide would quickly flow out of the syringe.
18. Which gas has a greater density, carbon dioxide or air? How can you tell? (Hint: Compare the molar masses of oxygen and nitrogen with that of carbon dioxide.)
    Carbon dioxide has a greater density than air. You can compare the molar mass of carbon dioxide to the major components of air. Air is mostly nitrogen (MM = 28 g/mol) and oxygen (MM = 32 g/mol) compared to carbon dioxide with a molar mass of 44 g/mol.
19. Design an experiment to determine whether carbon dioxide or air has the greater density.
    One possible response is to have two syringes filled with carbon dioxide and a third syringe containing air. Hold one of the carbon dioxide syringes upright as in Part 5 of the experiment and the other upside down. Put a lighted candle in each syringe. A candle in the upright syringe with the carbon dioxide will be extinguished as in the experiment. A candle in the carbon dioxide syringe held upside down will burn because the carbon dioxide was “poured” out of the syringe. The air syringe will serve as a control.
20. Suggest an experiment to determine how long the CO₂(g) will remain in an open syringe that is held upright. Will the CO₂(g) remain in the syringe for five minutes?
    One possible response is to have several syringes filled with carbon dioxide. Lower a lighted candle into each syringe at a different time interval; for example, after 1 minute for the first, 2 minutes for the second, etc. . . . The candle flame being extinguished provides evidence that there is still CO₂ remaining in the syringe. Continue with as many syringes needed until the candle remains lit when lowered, evidence that the CO₂ has escaped.

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 3.

Introduction

Prepare carbon dioxide gas, perform the classic limewater test for the detection of carbon dioxide, and observe its acidic nature. Watch the gas undergo a chemical reaction and determine if carbon dioxide supports combustion of a candle flame.

Concepts

• Gases
• Preparation of carbon dioxide gas
• Properties of carbon dioxide gas

Background

Carbon dioxide is a colorless gas present in our atmosphere at very low levels. It is essentially odorless, however it causes a sharp sensation when inhaled in concentrated doses. This may be noticed if the fizzy bubbles from a freshly poured carbonated beverage are inhaled.

Carbon dioxide was discovered over 250 years ago by an Englishman named Joseph Black. He prepared and characterized samples of CO₂(g) which he called fixed air. He found that “fixed air” could be produced by heating chalk which lost mass during the heating process. We now know this reaction is

Black also produced CO₂(g) by the action of acids on carbonates, fermenting vegetables and burning coal. In this experiment, CO₂(g) will be prepared by the action of acids on carbonate salts. In particular, sodium bicarbonate (baking soda) will be reacted with dilute hydrochloric acid, HCl(aq)

Other carbon-containing fuels such as gasoline and natural gas produce CO₂(g) and H₂O(g) upon combustion. Natural gas is primarily methane, CH₄(g), and its combustion reaction is

It is known that CO₂(g) in the upper atmosphere traps heat and thus acts like a global blanket. The sun warms the surface of the Earth and the heat normally radiates back out into space. Because low levels of CO₂(g) are naturally present in the Earth’s atmosphere, a certain amount of this blanket effect is normal. However, the widespread combustion of fossil fuels in our modern world has produced vast quantities of CO₂(g), thus thickening the blanket. A majority of the heat energy ends up trapped in our atmosphere. In this past century, the amount of CO₂(g) in our atmosphere has increased to the point where scientists are concerned that our planet is slowly warming up. This phenomenon is called the greenhouse effect which may eventually lead to global warming. Our neighboring planet Venus has an atmosphere of mostly CO₂(g) which is one of the main reasons that the surface temperature of Venus is about 860 °C.

Carbon dioxide has many important commercial uses. It is used in fire extinguishers, the soft drink industry, and as a chemical reagent to make other compounds. The major industrial use of carbon dioxide is as a refrigerant (accounting for over 50%). Dry ice, CO₂(s), was first commercially introduced as a refrigerant in 1924. Dry ice sublimes to a gas at –78.5 °C at standard pressure. By the 1960s, dry ice was replaced by liquid CO₂ (commonly called liquid carbonic) as the most common CO₂ refrigerant. Carbon dioxide has a melting point of –56.6 °C at 5.2 atmospheres. Liquid CO₂ is used to freeze materials such as hamburger meat and metals. It is also used to rapidly cool loaded trucks and rail cars. Another 25% of all CO₂ produced is used in the soft drink industry. Carbon dioxide is also widely used as a replacement for the propellant in aerosol cans which were formerly charged with chlorofluorocarbons (CFCs).

The solubility of CO₂(g) in water is 3.48 g/L at 0 °C and 1.45 g/L at 25 °C. When CO₂(g) dissolves in water, it produces CO₂(aq) for the most part:


Solutions of CO₂(aq) last longer if they are kept cool. As the solution of CO₂(aq) is warmed, CO₂(g) is released as bubbles. This is noticeable when a carbonated beverage is warmed. A very small portion of CO₂(aq) reacts with water to produce carbonic acid, H₂CO₃:

For this reason, CO₂(aq) is described as being “weakly acidic.” Two extremely important anions are the result of CO₂/water chemistry. The bicarbonate ion, HCO₃^–, (also called hydrogen carbonate) and the carbonate ion, CO₃^2–, have a vast and useful chemistry. It is the interaction between these two anions that functions as the buffer system in blood. Both are made when CO₂(aq) reacts with an alkaline (basic) solution, such as NaOH(aq): 

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. Ammonium hydroxide and hydrochloric acid solutions are toxic by inhalation, ingestion and are corrosive to all body tissues. Ammonia fumes can burn nasal membranes; always handle ammonia solutions in an operating fume hood. Use care when using matches. Sodium hydroxide is corrosive to all body tissues; handle with care. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Part 1. Preparation of Carbon Dioxide 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 0.22 g of NaHCO₃ and place 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.
   {11914_Procedure_Table_2}
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.
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 1 M HCl into a small beaker.
8. Draw about 5 mL of 1 M HCl 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.
   {11914_Procedure_Table_3}
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.
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.
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 CO₂ gas, it is necessary to wash the inside of the syringe in order to remove excess reagents. Follow the steps below and repeat if necessary. 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. Classic Test for Carbon Dioxide

1. Use about 15 mL of CO₂ gas from Part 1 for this part of the experiment.
2. Pour 10–15 mL of limewater into a small beaker (a test tube will also work). Complete the following steps as soon as possible after receiving the limewater. If exposed to air for too long, the limewater will begin to get cloudy.
3. Remove the syringe cap and quickly attach a piece of latex tubing to the syringe.
4. Bubble about 10–15 mL of the CO₂ gas from the syringe into the limewater. Tilt the syringe to prevent any liquids from being dispensed.
5. Record your observations on the data sheet.

Part 3. Carbon Dioxide and pH

1. Use about 45 mL of CO₂ gas from Part 1 for this part of the experiment.
2. Fill a small beaker about half full with distilled or deionized water.
3. Add about 20 drops (or 1 mL) of universal indicator to the beaker containing the water. Record the color and pH on the data sheet. Set the solution aside. It will be used in step 5.
4. Remove the cap from the 6 M NH₄OH solution and remove a pipetful of the ammonia fumes from above the surface. Do this by emptying and filling the pipet several times above the liquid. Do not remove any of the liquid.
5. Bubble the ammonia vapor through the indicator solution. Set solution aside again. It will be used in step 8.
   {11914_Procedure_Table_7}
6. Record the color and pH of the universal indicator solution on the data sheet.
7. Remove the syringe cap and attach a piece of latex tubing to the syringe.
8. Slowly bubble the remaining CO₂ gas from the syringe into the universal indicator solution.
9. Record the color, the pH of the universal indicator solution, and other observations on the data sheet.

Part 4. Reaction of Carbon Dioxide and Sodium Hydroxide

1. Prepare another syringeful of CO₂ gas by repeating the procedure from Part 1. At least 45 mL of CO₂ gas is needed for this part of the experiment.
2. Pour about 10 mL of 6 M NaOH solution into a small beaker.
3. Remove the syringe cap and draw 5 mL of NaOH into the syringe.
4. Securely place the syringe cap back on the tip of the syringe.
5. Gently shake the syringe to begin the reaction. The reagents will mix causing the reaction to proceed.
6. Record your observations on the data sheet.

Part 5. Does Carbon Dioxide Support Combustion?

1. Prepare a third syringeful of CO₂ gas by repeating the procedure from Part 1. This experiment requires 60 mL of CO₂ gas.
2. Tape a small candle to a glass stirring rod and set the apparatus aside. Make sure the tape is closer to the bottom of the candle than the top.
3. Use a ring stand and clamp to hold the syringe in a vertical position with latex syringe cap in place and plunger up. Remove the plunger by gently pulling it out of the syringe.
4. Light the candle. Lower the lit candle completely into the syringe barrel using the glass rod. (Caution: Be careful not to burn your fingers. Allow the glass rod to cool before removing the candle—hot glass looks like cold glass.)
5. Record your observations on the data sheet.
6. Excess CO₂ can be released into the air. Consult your instructor for appropriate disposal procedures for all other materials.

Student Worksheet PDF

11914_Student1.pdf