Chemical Science Lesson Plan

Title: Acid Rain Formation

Grade Level: 5

Prepared by: John Ha
Science standards

Science background for teachers

Introduction

Activity procedure

Materials

Summary and discussion


Objectives: Objectives:

Students will:
  • Know how a coal-fired power plant works.
  • Know that sulfur contaminants from coal lead to acid formation.
  • Understand how burning coal relates to acid rain.


Science standards


11.B.1a Given a simple design problem, formulate possible solutions.
11.B.1d Test the device and record results using given instruments, techniques and measurement methods.
11.A.2b Collect data for investigations using scientific process skills including observing, estimating and measuring.
11.A.2d Use data to produce reasonable explanations.
11.A.2e Report and display the results of individual and group investigations.
11.B.2b Develop a plan, design and procedure to address the problem identifying constraints (e.g., time, materials, technology).
11.B.2c Build a prototype of the design using available tools and materials.
11.B.2d Test the prototype using suitable instruments, techniques and quantitative measurements to record data.
11.B.2f Report test design, test process and test results.
12.C.1a Identify and compare sources of energy
13.b.1d Identify and describe ways that science and technology affect people's everyday lives.

Science background for teachers


The chemical smoke expelled from various coal-burning power plants causes problems in the environment in many ways, including production of acid rain. The major problem comes from the gas that is released into the air that we breathe when dirty coal is burned. Although coal is mainly composed of carbon, it contains impurities such as sulfur and nitrogen atoms. These atoms such as carbon, nitrogen, and sulfur are released with smoke as gases.

All the gas compounds from the smoke accumulate in our closest atmosphere of Earth called, troposphere, and go through various kinds of chemical reactions in presence of oxygen and water as described below. Of all gases, nitrogen oxide and sulfur oxides play a big role in producing acid rain. Also, some of the greenhouse gases are produced such as carbon dioxide, methane, chlorofluorocarbons, etc. Greenhouse gases are known to cause global warming, which is dramatic temperature increase and climate change that is an issue today.

Some of the gases like nitrogen oxides chemically react with sunlight in the air and produce harmful airborne particles known as Photochemical smog. Photochemical smog is a serious health hazard in that they cause illnesses such as lung conditions, emphysema, bronchitis, asthma, weakening body immune system, and even death. In this experiment we will specifically focus on nitrogen oxides and sulfuric oxides present in the smoke when burning un-purified coal that can cause acid rain.

Acid rain happens when gas pollutants such as nitrogen oxides and sulfur oxides react with water molecules in the atmosphere; the chemical reaction of sulfur oxide turning into sulfuric acid is described below. Sulfuric acid is delivered Earth when it precipitates with rain or snow. When it rains as an acid rain, this is called wet deposition of acid. Acidic rain is harmful to humans and environments. Acid rain can disrupt the aquatic ecosystem by affecting the reproduction and survival of aquatic organisms that cannot survive acidic conditions. Acid rain also damages soil by disabling some of the important organisms’ ability to maintain healthy soil. Acid rain can cause toxins to spread in the soil and also leach away important minerals nutrients from soil. Students will see how acid rain is produced by smoke released by coal powered plants through this experiment.

Nitrogen dioxide:
Sulfur dioxide:

Coal; Fossil Fuel

Fossil fuel is an energy source that is used widely in the world. Examples are heating for houses, fueling automobiles, and other energy sources. Types of fossil fuels include coal, petroleum, and natural gas. In this activity we are focusing on the coal. Coal is a natural resource that forms with geological steps over millions of years. The first step of coal formation is the formation of what is called the peat, which is formed by decomposition of organisms. However, peat cannot be used as a fuel because it is too wet. The peat must have a protective layer of sediment on top so the moist is prevented and it becomes denser. Depending on the quality of coal, there are three different classifications (lowest to highest quality): lignite, bituminous, and anthracite. The quality depends on the amount of carbon in the coal. The higher quality coal burns more efficiently and cleanly. The coal powered power plants use it to generate electricity. The coal is burned to produce heat to boil water and steam. The steam turns a turbine connected to a generator, which generates electricity. Coal burning produces gases that contain primarily carbon, sulfur, nitrogen, hydrogen, and oxygen. We will focus on the sulfur oxides and carbon dioxides’ effects to the formation acid rain. The burning of charcoal and sulfur produces smoke similar to that of many coal-fired power plants. The smoke precipitates with water as acid rain, which is what we produced in the water in the beaker with the smoke dissolved in it. The acidity is apparent and we can see what it is capable of doing to the environment by observing the dissolving of a piece of chalk.

Note: Charcoal is used in this simulation because it is a form of coal in that they both contain a lot of carbon.

There are three main chemical reactions that are relevant to our acivity.
  1. Combustion reaction:
      Combustion reaction describes what happens when the charcoal is burned with fire in presence of oxygen. The charcoal contains carbon, which becomes carbon dioxide when reacted with oxygen with heat. The carbon dioxide can easily be dissolved in water and form carbonic acid, which is explained in the next step. The below shows a balanced reaction of carbon dioxide formation.

      C + O2 CO2

      (12 kg C) + (32 kg O) (34 kg CO2)

  2. Carbonic acid (H2CO3) formation:
      Carbon dioxide is a major product of coal combustion reaction. Carbon dioxide in atmosphere reacts with water. When CO2 gas dissolves in water molecules, carbonic acid forms. The below shows each chemical reactions that take place in formation of carbonic acid from carbon dioxide. Carbonic acid is a diprotic acid. It dissociates one protons to make bicarbonate and another proton to make carbonate.

      CO2 + H2O H2CO3

      H2CO3 H+ + HCO3-

      HCO3- H+ + CO32-

    * In the demonstration, carbon dioxide formed from burning charcoal will not change the concentration of carbonic acid in the water because the water is already saturated with CO2.

  3. Sulfuric acid (H2SO4) formation:
      Coal contains many impurities and sulfur is one of them. When coal is burned the sulfur combines with oxygen and the sulfur oxides are released to the atmosphere. Sulfur dioxide (SO2) becomes sulfur trioxide (SO3) when reacting with oxygen in the air. This reacts with water molecules in the atmosphere to form sulfuric acid, a strong mineral acid. This makes rain acidic. In our demonstration, the smoke is transferred directly to the water in the beaker to form sulfuric acid. The below shows the chemical reactions that take place in formation of sulfur trioxide, which reacts with water to form sulfuric acid.

      2 SO2 + O2 2 SO3

      SO3 + H2O H2SO4

      H2SO4 H+ + HSO4-

Overall Scheme of the demonstration: The coal-fired power plants involve above chemical reactions to burn coal and produce electricity. The coal is mainly composed of carbon; however, the coals used in power plants are not completely purified. Unpurified coals are simulated by mixing charcoal and sulfur powder together. These will release smoke containing carbon dioxide and sulfur dioxide when burned using combustion reaction. The carbonic acid will not form because the tap water is saturated with carbon dioxide already so it will not mix with additional carbon dioxide. However, sulfur dioxide will mix in the water and form sulfuric acid as described. This will turn the water acidic and will be able to dissolve chalk by chemical reaction described above. It is important that you follow the procedure carefully with correct amount of each material to successfully create acidic water through this method.

Introduction

The goal of this activity is to simulate a coal burning power plants and how it can cause environmental harm by producing acid rain.

Can you tell me some facts about coal and why power plants use this?

Let's see what coal's nature is.

The coal is considered an organic compound that is mainly made up of carbons. This stores a lot energy that can be released when burned in fire, which is what they do in these power plants. These power plants use coal to produce heat, which boils water to produce steam. Steam is used to generate a turbine connected to an electricity generator. This is where our electricity from houses and buildings come from.

So how can these power plants affect environment?

To answer this question we need to know what the smoke produced from coal burning is made up of.

Coal burned in these power plants produce smoke that is released in mass amounts in the atmosphere. The power plants use coals that are not completely clean, so it contains impurities. Impure coal burning produces smoke that contains a lot of chemicals, which can harm the environment by producing acid rain. We will focus on carbon dioxide and sulfur oxides that are in the released smoke. Carbon dioxide is produced in excess amounts. This gas is already present in our atmosphere but in excess amounts, it can cause global warming, increasing the global temperature abnormally. Sulfur oxides are another type of gas that is released with the smoke. When this is present in the atmosphere it can be one of the prime causes of acid rain on Earth. Acid rain in real life can be harmful for the plants and aquatic organisms in rivers and lakes.

Tell me about what you think acid means.

Let's see how we can simulate coal burning power plants by experimenting with charcoal and sulfur to produce acid water.

(Show the demonstration with charcoal and test the acidity with the pH indicator. The pH should be neutral and explain that this is because only carbon dioxide is produced from burning clean carbon matter, charcoal, which is not the carbon matter of power plants; dirty coal. So tell the students that the sulfur is one of the impurities in coal and ask them to do the activity and test the acidity.)

We are using charcoal to represent the coal used in these power plants since they both have similar elements. Charcoal by itself will only produce carbon dioxide, so we will be adding the sulfur to the charcoal to simulate impurities present in coals. When these are burned together, they release the smoke that contains carbon dioxide and sulfur dioxide, which are also present in smoke released by power plants. The gas will be directly mixed into water, just as they do in the atmospheric water molecules. The gas will produce acidic water and it represents the acidic rain coming down from the atmosphere. Once the acidic water is produced from the burning of sulfur and charcoal, we will be dissolving a piece of chalk to observe the effects of acid rain in real life. The chalk is calcium carbonate, which is present in the environment as limestone rocks. These rocks do not usually dissolve in neutral water, but can be dissolved in acidic water, therefore, they are affected by acid rain. One thing to note is the charcoal itself does not make the water acidic because the water is already saturated with carbon dioxide, so the addition of sulfur is crucial.

How would you test the acidity of a substance?

We will be using a pH indicator that can tell us what the acidity of water is. (Have the students to the experiment with sulfur addition on their own and test the pH level.)

The acidity is tested with a pH indicator strip, which shows the pH level of water by showing different colors according to the acidity. pH level below 7 indicates acidity while above that indicates basicity and pH 7 is neutral, which is what our tap water is. If acid water can dissolve rocks, you may imagine what acid water can do to organisms that usually live in neutral water.

(Ask the students what they think actually promotes production of acid rain from power plants?)

The coal-fired power plants produce smoke that contains harmful gases such as carbon dioxide and sulfur oxide. From the experiment you should understand that coal impurities such as sulfur, producing gas sulfur oxide reacts with water in the atmosphere and come down Earth as acid rain. This is how the coal-fired power plants harm the environment!

Activity procedure


Demonstration

The demonstration involves working with matches so students must be well supervised.

We use an apparatus is a metal coffee can with holes poked at the side top (air exit) and side bottom (air entrance) with plastic tubes glued into each. A steel screen forms a burning platform inside the can. The top is sealed with the plastic can lid. A piece of paper and a piece of aluminum foil are under the plastic to prevent it from burning. A simple air pump (bellows type) pushes air through the coffee can and supports combustion. The exit tube is put below the water line in a glass jar with about 50 mL water. The air from the combustion chamber bubbles through the water.

  1. Fill up the beaker with 50 mL of water and place it on the beaker holder
  2. Turn on the air vacuum
  3. Sink one of the air tubes into the water
  4. Weigh 1 gram of charcoal on the weighing boat
  5. Place the charcoal on top of a small piece of Kimwipe and spray oleic acid
  6. Wrap the charcoal with the Kimwipe and place it (using a tweezer) inside the coffee can on top of the steel mount
  7. The coffee can should have two tubes connected to it. One tube goes inside the water beaker and the other tube is connected to the air vacuum.
  8. Light a match and place it on top of the charcoal
  9. Wait until the Kimwipe is burned off and charcoal is lit up
  10. Place the lid on top of the can and close with the plastic lid
  11. Wait for 10 minutes
  12. Test the pH of the water with a pH indicator strip
  13. Once the acidity is confirmed, drop a small piece of chalk and observe what happens

Activity

  1. Get into groups of five students
  2. Each group will write up their own procedure of how to demonstrate coal burning with addition of sulfur.
  3. Groups must set up the simulation and successfully produce an acidic water produced by the coal combustion.
  4. Groups must hypothesize the effects of adding sulfur into the coal burning.
  5. Observe the effects of sulfur by testing the water with a pH indicator strip and see what happens to the piece of chalk in the water.


Materials



steel screen plastic tubing air pump
beaker pH indicator olive oil
tweezers, spatula coffee can, lid plastic tubing
charcoal sulfur weighing boat, scale


Summary and discussion


a) What are some gases that are emitted from coal power plants?
    (Answer: Carbon dioxide, sulfur oxides, nitrogen oxides, etc.) *Students should know about the carbon dioxide and sulfur oxides from reading the introduction.

b) What are some ways that acid rain can harm the environment?
    (Answer: Killing organisms in surface waters, harmful to plants, and etc.)

c) How can we prevent acid rain? List three possible solutions.
    (Answer: Use cleaner coal that contains less sulfur)

d) What pH level is considered acidic?
    (Answer: pH level of below 7)

e) Does chalk dissolve in normal water? If not, how did water from burning coal with sulfur dissolve chalk?
    (Answer: No. Burning sulfur produced sulfuric oxide, which reacted with water to form acidic water. Only when the water is acidic, does the chalk dissolve.)

EnLIST Chemistry Workshop, University of Illinois, 2010