Acid Rain in a Bag

Introduction

Perform a safe, microscale simulation of acid rain formation.

Concepts

  • Oxidation–reduction
  • Indicators
  • Environmental chemistry
  • Acid rain

Materials

Copper wire, 7 cm*
Nitric acid, HNO3, 8 M, 25 mL*
Universal indicator solution, 100 mL*
Overhead projector
Pipets, Beral-type, 14*
Reaction plate, 24-well*
Zipper-lock bags, 1-gallon size, 2*
*Materials included in kit.

Safety Precautions

Please review relevant Safety Data Sheets before beginning this activity. Nitric acid is corrosive and is a strong oxidizer. Nitrogen dioxide is a poisonous gas. Do not inhale. Open bag in a well-ventilated area or in a fume hood. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron.

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. Rinse out the bag with an excess amount of water and pour down the drain according to Flinn Suggested Disposal Method #26b.

Procedure

  1. Place a one-centimeter piece of copper wire in one of the center wells of a 24-well reaction plate.
  2. Using a Beral-type pipet, place a few milliliters of universal indicator solution in each of the four corner wells of the 24-well reaction plate. Fill the remaining wells with distilled or deionized water.
  3. Place the reaction plate into the zipper-lock bag and place the bag on the overhead projector.
  4. Turn the overhead on and focus the projector so the color of the indicator is visible.
  5. Using a Beral-type pipet, carefully place about 12 drops of 8 M nitric acid in the same well as the copper wire.
  6. Quickly but carefully, zip up the bag so it is completely closed.
  7. Observe the color changes of the indicator, the center well and the production of nitrogen dioxide.
  8. Use a few drops of the universal indicator or pH paper to test the water in the remaining wells at various distances from the center.

Student Worksheet PDF

12264_Student1.pdf

Teacher Tips

  • Students should be familiar with the color of the universal indicator at various pH levels. As the reaction occurs in the bag, the students should recognize that the changes in the color of the universal indicator reflect a decrease (acidification) of the pH.

Correlation to Next Generation Science Standards (NGSS)†

Science & Engineering Practices

Developing and using models
Obtaining, evaluation, and communicating information
Analyzing and interpreting data
Constructing explanations and designing solutions

Disciplinary Core Ideas

MS-PS1.A: Structure and Properties of Matter
MS-ESS3.C: Human Impacts on Earth Systems
HS-PS1.B: Chemical Reactions
HS-ESS3.C: Human Impacts on Earth Systems

Crosscutting Concepts

Cause and effect
Structure and function
Systems and system models

Performance Expectations

MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
MS-ESS3-3: Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment.
HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
MS-ESS3-4: Construct an argument supported by evidence for how increases in human population and percapita consumption of natural resources impact Earth’s systems.

Answers to Questions

  1. Draw the reaction plate used in this demonstration. Label each well with the substance it contained originally. Also note the final color in each well and any other observations.
    {12264_Answers_Figure_1}

    A red-brown gas was also produced inside the zipper-lock bag.

  2. Write the balanced chemical equation for the reaction between copper metal and nitric acid to produce nitrogen gas, in addition to other products.

    Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)

  3. Explain why the universal indicator changes from its natural green-blue to red.

    The red-brown gas produced by the reaction between copper metal and nitric acid is nitrogen dioxide gas. Nitrogen dioxide gas dissolves in aqueous solutions and produces a very acid solution. The universal indicator turns red because of the high acidity.

  4. How does this activity demonstrate the formation of acid rain?

    Nitrogen dioxide, the pollutant produced in this experiment, is emitted by cars and factories. The gas then dissolves in the water vapor in the sky, lowering the pH in the vapor and eventually producing acid rain, just like the gas given off in this experiment dissolved in the aqueous solutions around it.

Discussion

A chemical reaction occurs when copper is covered with nitric acid. The nitric acid is not only a strong acid but also a strong oxidizing agent. The copper metal undergoes a redox reaction and is converted to copper(II) ions in solution. The nitric acid is reduced to nitrogen dioxide gas. Water is also formed in the reaction.

Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)

The universal indicator solution in the outside wells changes color as the pH falls. The nitrogen-dioxide gas that is produced dissolves readily in aqueous solutions, producing a very acidic solution. By testing the water placed in several of the other wells, students will clearly see that it has been acidified by the nitrogen dioxide gas.

Students should notice the orange-brown colored nitrogen dioxide, the blue colored copper(II) nitrate in the center well, and the now red-colored universal indicator solution.

This experiment demonstrates, on a small scale, the effect of the production of nitrogen dioxide. Nitrogen dioxide is a pollutant produced by cars and manufacturing facilities. When it dissolves in water vapor and falls to the Earth, it is called acid rain.

References

Berger, S. A., Hill, A. E., Holmquist, R. K., Horsch, E. A. Element of the Week. Flinn Scientific: Batavia, IL. 1989.

Recommended Products

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AP9157 Acid Rain in a Bag—Demonstration Kit

†Next Generation Science Standards and NGSS are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.