Materials Included In Kit

Additional Materials Required

Safety Precautions

Hydrochloric acid is slightly toxic by ingestion or inhalation and is corrosive to skin and eyes. Keep spill control materials on hand to clean up chemical spills. Hydrogen peroxide is a skin and eye irritant. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles and chemical-resistant gloves and apron. Never sniff any substance in the chemical laboratory—to detect the odor of a substance, place the open container about 6 inches away from the nose and use your hand to waft the vapors toward the nose. Please consult current Safety Data Sheets for additional safety, handling and disposal information. Remind students to wash hands thoroughly with soap and water before leaving the lab.

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 acid solutions may be neutralized with base and disposed of according to Flinn Suggested Disposal Method #24b. The waste solutions may be flushed down the drain with plenty of excess water according to Flinn Suggested Disposal Method #26b.

Lab Hints

• The laboratory work for this experiment can easily be completed within a typical 50-minute lab period. The activity is very versatile and can be used in many different places in the physical science curriculum. Use the experiment to introduce physical and chemical properties, to review the periodic table, provide experience in writing and balancing chemical equations or illustrate the properties of common gases.
• Demonstrate the wafting technique to your students and remind them to never sniff a chemical in the laboratory.
  {13969_Hints_Figure_1}
• The use of a graduated cylinder and precise amounts is not necessary but does provide good laboratory protocol for following directions and making precise measurements. If graduated cylinders are not available, have students add one finger’s width, two finger‘s width, etc., as the measurement amount.
• Demonstrate how to correctly light a splint, place it into the test tube, and then extinguish it. Also demonstrate how to prepare a glowing splint.
• As noted, step 11 must be done quickly to observe the characteristic “pop” test for hydrogen gas. Hydrochloric acid is in excess in the test tube. If students fail to observe the hydrogen reaction the first time, have them try again with a fresh piece of magnesium ribbon.
• Remind students to rinse the graduated cylinder with distilled or deionized water between additions.

Teacher Tips

• Hydrogen gas may be generated and collected using the reactions shown in this experiment. Construct a gas generator using a small test tube, 1-hole rubber stopper and a graduated, Beral-type pipet. Cut the pipet as shown, construct the gas delivery tube, and fill the pipet bulb with water. Place 0.5 g of magnesium into the test tube and fill the test tube about ¾ full with 1 M hydrochloric acid. Replace the rubber stopper and collect the hydrogen gas by water displacement. To test for hydrogen, collect a pipet-bulb full of the gas, place a burning splint near the mouth of the pipet bulb, and quickly squeeze the bulb. A large pop will be heard and the flame will quickly extinguish.
  {13969_Tips_Figure_2}
• The common gases prepared in this experiment provide a good starting point for describing the chemistry of the atmosphere. Possible topics for discussion include the composition and properties of gases in the atmosphere, the reactions of carbon dioxide that are involved in the carbon cycle, and the role of carbon dioxide in global warming.
• Why does hydrogen give the characteristic “pop” test? Hydrogen by itself should not react. The slight popping sound occurs as hydrogen escaping from the test tube mixes with oxygen in the air. Eventually a combustible H₂/O₂ mixture is produced.

Answers to Prelab Questions

1. Read the entire Procedure and the Safety Precautions. What is the proper procedure for smelling a chemical in the lab?

   Never sniff any chemical in the lab. To observe the odor of a substance, hold the container about 6 inches away from the nose and use your hand to carefully waft the vapors toward the nose.

2. Complete the following balanced equations for the reactions in test tubes A–C. Enter the name and formula of each gas in the data table.
   1. {13969_PreLabAnswers_Equation_4}
   2. {13969_PreLabAnswers_Equation_5}
      Note: Manganese dioxide, MnO₂, helps speed up the reaction but does not undergo chemical change. Substances that do this are called catalysts. They are not included in a chemical equation.
   3. {13969_PreLabAnswers_Equation_6}

Sample Data

Answers to Questions

1. Identify the common gas or gases prepared in this experiment:
   {13969_Answers_Figure_3}
2. Explain the observations in the glowing splint test for oxygen.

   The glowing splint burst into flame because combustion occurs faster in pure oxygen than in air.

3. Circle and label the physical and chemical properties of chlorine in the following description:

   “Chlorine is a greenish-yellow gas that dissolves in water and is toxic to humans. It combines violently with sodium metal to form sodium chloride, a white solid that melts at 800 °C.”

   {13969_Answers_Table_2}
4. Consult a Periodic Table: Name the elements that exist as gases at room temperature and give their symbols or formulas. Hint: Some elements, such as nitrogen, exist as diatomic or two-atom, molecules (e.g., N₂) in their free state.

   Hydrogen (H₂), helium (He), nitrogen (N₂), oxygen (O₂), fluorine (F₂), neon (Ne), chlorine (Cl₂), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn).

5. 1. Which gaseous elements (see Question 4) are toxic?

      The halogens (fluorine and chlorine) are toxic. Radon is radioactive and is thus a radiation hazard.

   2. Which gaseous elements are considered inert or unreactive?

      The Noble Gases (helium, neon, argon, krypton, xenon and radon) are considered inert or unreactive. Note: Under extreme conditions, krypton and xenon will react to form compounds of the type KrF₂ and XeO₃.

References

This experiment is adapted from Flinn ChemTopic™ Labs, Volume 8, Chemistry of Gases; Cesa, I., Ed., Flinn Scientific: Batavia, IL (2003).

Introduction

Although many gases are colorless and odorless, they are not all the same. If we think about how different gases in the atmosphere affect the environment, we realize that different gases have different physical and chemical properties. Let’s look at the properties of some common gases.

Concepts

• Physical property
• Chemical property

Background

Pure substances, whether solid or liquid or gas, have a constant composition or chemical makeup. Solid copper metal (Cu), liquid water (H₂O) and gaseous carbon dioxide (CO₂) are examples of pure substances. Pure substances have characteristic physical and chemical properties that can be used to describe them. A physical property is a characteristic of matter that can be observed or measured without changing the chemical composition. Examples of physical properties include color, odor, physical state (at room temperature), conductivity, melting point, boiling point and solubility. A chemical property describes the ability of a substance to undergo changes in its chemical composition. Examples of chemical properties include flammability, acidity and corrosion.

Experiment Overview

The purpose of this experiment is to prepare three common gases and observe their physical and chemical properties.

Materials

Prelab Questions

1. Read the entire Procedure and the Safety Precautions. What is the proper procedure for smelling a chemical in the lab?
2. Complete the following balanced equations for the reactions in test tubes A–C. Enter the name and formula of each gas in the data table.
   1. {13969_PreLab_Equation_1}
   2. {13969_PreLab_Equation_2}

      Note: Manganese dioxide, MnO₂, helps speed up the reaction but does not undergo chemical change. Substances that do this are called catalysts. They are not included in a chemical equation.

   3. {13969_PreLab_Equation_3}

Safety Precautions

Hydrochloric acid is slightly toxic by ingestion or inhalation and is corrosive to skin and eyes. Notify your teacher and clean up all spills immediately. Hydrogen peroxide is a skin and eye irritant. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Never “sniff” any substance in the chemical laboratory—to detect the odor of a substance, place the open container about 6 inches away from your nose and use your hand to waft the vapors toward your nose. Wash hands thoroughly with soap and water before leaving the lab.

Procedure

1. Label three medium test tubes A–C and place them in a test tube rack.
2. Using a 10-mL graduated cylinder, add 2 mL of 0.1 M sodium bicarbonate into test tube A. Note: Use a graduated cylinder to make all measurements. Make sure to rinse the graduated cylinder with distilled or deionized water before adding each new chemical.
3. Add 2 mL of 1 M hydrochloric acid into test tube A and observe the color and odor of the gas. Remember to waft. Record the observations in the data table. Note: If the gas has no color or odor, write colorless or odorless, respectively.
4. Light a wood splint and insert the burning splint well down into the test tube (but NOT into the liquid). Record the observations in the data table. Note: Fill a 150-mL beaker with tap water to use as your extinguishing flask. Place all burning splints or matches in this beaker after use.
5. Pour 5 mL of 3% hydrogen peroxide solution into test tube B.
6. Using a splint as a spatula, add a small amount (about the size of a grain of rice) of manganese dioxide to test tube B and gently swirl the test tube to initiate the reaction. Observe and record the color and odor of the gas in the data table.
7. Seal the mouth of test tube B by stretching a piece of Parafilm^® over the top of the tube. Allow the test tube to sit undisturbed for 1–2 minutes.
8. Prepare a burning wood splint.
9. Remove the Parafilm from the test tube. Quickly blow out the splint so that it is glowing rather than burning. Insert the glowing splint down into the test tube almost to the liquid, then bring it out. Extinguish the splint. Record your observations in the data table.
10. Carefully add 5 mL of 1 M hydrochloric acid to test tube C.
11. One member of the team should strike a match, and the other member should carefully add one piece of magnesium ribbon into the acid in test tube C. Quickly place the lighted match directly above the mouth of the test tube. Extinguish the match. Record your observations, including the color and odor of the gas, in the data table.
12. Dispose of the contents of test tubes A–C as directed by your instructor.

Student Worksheet PDF

13969_Student1.pdf