Materials Included In Kit

Additional Materials Required

Prelab Preparation

Using scissors, cut 5-mm squares from the copper foil strip for each lab group. From the magnesium ribbon, cut 2-mm lengths.

Safety Precautions

Nitric acid solution is severely corrosive and a strong oxidizing agent. Work with nitric acid in a fume hood only and do not remove from the hood. Hydrochloric acid solution is toxic by ingestion or inhalation and is corrosive to skin and eyes. Sodium hydroxide solution is a corrosive liquid and is especially dangerous to eyes. Keep spill control materials on hand to clean up chemical spills. Hydrogen peroxide solution is a skin and eye irritant. Avoid contact of all chemicals with eyes and skin. Copper foil edges are sharp and may cause cuts; handle with care or use forceps. Wear chemical splash goggles and chemical-resistant gloves and apron. Never directly 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 sodium hydroxide solution may be neutralized with acid and disposed of according to Flinn Suggested Disposal Method #10. 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 chemistry curriculum. Use the experiment to introduce physical and chemical properties, to review the periodic table, to provide experience in writing and balancing chemical equations or to illustrate the properties of common gases. The experiment is also well-suited to applications-oriented chemistry courses such as Chemistry in the Community.
• A good “rule of thumb” for students to learn—all colored gases are toxic!
• The acids used for the preparation of nitrogen dioxide and hydrogen have been chosen with safety in mind. Although copper metal gives a faster reaction with concentrated nitric acid, using 6 M nitric acid is safer. In addition, the slower reaction allows students to observe the actual changes taking place in the reaction mixture as the reaction proceeds. Remind students not to remove the test tube from the hood.
• The reaction of copper metal with 6 M nitric acid is relatively slow. The solution turns blue-green within three minutes, and a brown gas is observed after five minutes. Place a piece of white paper behind the test tube to observe the color of the gas. The preparation of NO₂ may be done as a teacher-led demonstration, if desired.
• Demonstrate the wafting technique to your students and remind them never to directly sniff any chemical in the laboratory.
• Step 17 of the Procedure 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.
• To avoid long lines at the reagent bottles, create a separate lab station for each of the five test tube determinations. Have different student groups start at different stations to avoid conjestion.

Teacher Tips

• Hydrogen and oxygen may be generated using the reactions shown in this experiment and collected by water displacement if desired. See the experiment “Preparing and Testing Hydrogen Gas” in Volume 8 of the Flinn ChemTopic™ Labs series for a suitable microscale procedure.
• 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.
• Atmospheric chemistry represents an interesting application of chemistry as “the central science.” The common gases prepared in this experiment provide a good starting point for studying 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, the role of carbon dioxide in global warming, and the reactions of nitrogen dioxide that contribute to air pollution and the loss of the ozone layer.
• Parafilm is a thermoplastic, pliable, self-sealing film that can be used to seal almost anything. Cut into 3-cm squares for student use.

Answers to Prelab Questions

1. Read the entire Procedure and the accompanying Safety Precautions. What hazards are associated with the use of nitric acid?

   Nitric acid is severely corrosive and a strong oxidizing agent. Work with nitric acid in the fume hood only and do not remove from the hood. Wear chemical splash goggles and chemical-resistant gloves and apron and avoid contact with eyes and skin. Notify the teacher and clean up all spills immediately.

2. What is the proper procedure for smelling a chemical in the lab?

   Never directly 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.

3. Complete the following balanced equations for the reactions in test tubes A–E. Enter the name and formula of each gas in the data table.
   {13968_PreLabAnswers_Equation_1}

Sample Data

Answers to Questions

1. Identify the common gas or gases prepared in this experiment:
   1. Contributes to brown, industrial smog and air pollution? Nitrogen dioxide
   2. Lightest element in the universe? Hydrogen
   3. Needed for the burning of fossil fuels and for respiration in animals? Oxygen
   4. Dissolves readily in water and is used as a fertilizer? Ammonia
   5. Combustible? Hydrogen
   6. Extinguishes a flame? Carbon dioxide
   7. Has an odor? Ammonia and nitrogen dioxide (The latter is not based on student observation.)
   8. Required for photosynthesis? Carbon dioxide
2. Explain the observation of the glowing splint test for oxygen.

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

3. Explain the observations of the litmus test for ammonia.

   Litmus paper turned blue, indicating that ammonia is a basic substance.

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

   “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.”

   {13968_Answers_Table_1}
5. Consult a Periodic Table: Name the elements that exist as gases at room temperature and give their symbols or formulas. Hint: Recall that some elements exist as diatomic molecules 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).

6. (a) Which gaseous elements (see Question 5) are toxic? (b) Which gaseous elements are considered inert or unreactive?
   1. The halogens (fluorine and chlorine) are toxic. Radon is a radiation hazard.
   2. 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 laboratory is adapted from Flinn ChemTopic™ Labs, Volume 8, Chemistry of Gases; Cesa, I., Ed., Flinn Scientific: Batavia, IL

Introduction

It’s easy to overlook the chemistry of gases—because many gases are colorless and odorless, we may not notice them. If we reflect on the environmental impact of different gases in the atmosphere, however, we realize that not all gases are the same. Just like solids and liquids, all gases have characteristic physical and chemical properties. Let’s look at the properties of some common gases.

Concepts

• Physical properties
• Chemical properties

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 and analyze 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 five common gases and observe their physical and chemical properties.

Materials

Prelab Questions

1. Read the entire Procedure and the accompanying Safety Precautions. What hazards are associated with the use of nitric acid?
2. What is the proper procedure for smelling a chemical in the lab?
3. Complete the following balanced equations for the reactions in test tubes A–E. Enter the name and formula of each gas in the data table.
1. NaHCO₃(aq) + HCl(aq) → NaCl(aq) + H₂O(l) + ____ (g)
2. Cu(s) + 4HNO₃(aq) → Cu(NO₃)₂(aq) + 2H₂O(l) + 2 ____ (g)
3. NH₄Cl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l) + ____ (g)
4. 2H₂O₂(aq) → 2H₂O(l) + ______ (g)

   Note: The catalyst (MnO₂) is not represented in the balanced chemical equation.

5. Mg(s) + 2HCl(aq) → MgCl₂(aq) + ____ (g)

Safety Precautions

Nitric acid is severely corrosive and a strong oxidizing agent. Work with nitric acid in a fume hood only and do not remove from the hood. Hydrochloric acid is toxic by ingestion or inhalation and is corrosive to skin and eyes. Sodium hydroxide is a corrosive liquid and is especially dangerous to the 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. Copper foil edges are sharp and may cause cuts; handle with care or use forceps. Wash hands thoroughly with soap and water before leaving the lab. Never directly 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. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.

Procedure

Test Tube A 

1. Label five medium test tubes A–E and place them in a test tube rack.
2. Pour 2 mL of 0.1 M sodium bicarbonate into test tube A.
3. Add 2 mL of 3 M hydrochloric acid into test tube A and observe the color and odor of the gas. 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.

1. Bring test tube B to the fume hood and carefully add 1 mL of nitric acid to the test tube.
2. Place test tube B in a rack in the fume hood and add one small piece of copper foil. Observe and record the color of the gas in the data table. Caution: Do NOT attempt to smell the odor of the gas! Leave the test tube in the fume hood.

1. Add a small amount (about a spatula-full, approximately 0.1 g) of solid ammonium chloride to test tube C, followed by 5 mL of water. Stir with wood splint to dissolve the solid.
2. Place the test tube in a 150-mL beaker containing about 75 mL of hot tap water.
3. Add 10 drops of 3 M sodium hydroxide to test tube C. Gently swirl the test tube to mix the contents and cautiously observe the odor. Record the color and odor of the gas in the data table. Caution: To observe the odor, hold the test tube about 6–8 inches away from the nose and use your hand to waft the vapors toward you. Do NOT directly “sniff” the odor of any chemical in the laboratory.
4. Moisten a strip of litmus paper with a drop of distilled water and place the moistened litmus paper on top of test tube C. Record the color of the litmus paper in the data table.

1. Pour 5 mL of 3% hydrogen peroxide solution into test tube D.
2. Add a small amount (about the size of a grain of rice) of manganese dioxide to test tube D and gently swirl the test tube to initiate the reaction. Observe and record the color and odor of the gas in the data table.
3. Seal the mouth of test tube D by stretching a piece of Parafilm^® over the top of the tube. Allow the test tube to sit undisturbed for 1–2 minutes.
4. Prepare a burning wood splint.
5. 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 level of the liquid, then bring it out. Record your observations in the data table.

1. Carefully add 5 mL of 3 M hydrochloric acid to test tube E.
2. Strike a match, carefully add one piece of magnesium ribbon into the acid in test tube E, and quickly place the lighted match directly above the mouth of the test tube. Record your observations, including the color and odor of the gas, in the data table.
3. Dispose of the contents of test tubes A–E as directed by your instructor.

Student Worksheet PDF

13968_Student1.pdf