Diluting the Problem KEY CONCEPTS AND PROCESS SKILLS KEY VOCABULARY ACTIVITY OVERVIEW L A B O R ATO R Y B-137

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1 Diluting the Problem 40- to 3 50-minute sessions ACTIVITY OVERVIEW 24 L A B O R ATO R Y Students explore dilution as a disposal method for copper-containing solutions produced during circuit-board manufacturing. They construct a serial dilution of 100,000 ppm used copper chloride solution and add ammonia to demonstrate that chemical tests can reveal concentrations lower than those visible to the human eye. They then use the serial dilution for comparison in determining the concentration of the copper chloride waste from Activity 23, Producing Circuit Boards. KEY CONCEPTS AND PROCESS SKILLS (with correlation to NSE 5 8 Content Standards) 1. The amount of a contaminant in air or water is often expressed in parts per million or even parts per billion. 2. Toxic waste is harmful to living organisms and must be disposed of according to strict guidelines. (Perspectives: 4) 3. Students will use math in all aspects of scientific inquiry. (Inquiry: 1) KEY VOCABULARY concentration control dilution indicator parts per million (ppm) serial dilution B-137

2 Activity 24 Diluting the Problem MATERIALS AND ADVANCE PREPARATION For the teacher 1 Science Skills Transparency 2, Use of a Dropper Bottle 1 Literacy Transparency 3, Reading Scientific Procedures 1 Transparency 24.1, Diluting and Testing Copper Chloride (photocopy at 108%) 1 Transparency 24.2, Treating Waste Concept Map 1 transparency of Student Sheet 24.1, Determining Concentration 1 transparency of Student Sheet 24.2, Treating Waste * 1 overhead projector 2 plastic cups * 1 bottle of red food coloring * supply of water * 1 pair of disposable latex gloves * 1 pair of safety goggles * 1 funnel * 1 container for liquid waste For each group of four students 1 labeled 30-mL dropper bottle of each of the following: 100,000 ppm copper chloride solution water 5% ammonia solution used copper chloride solution from Activity 23, Producing Circuit Boards 1 cup of water For each pair of students 1 SEPUP tray 1 dropper 1 stir stick 1 copy of Transparency 24.1, Diluting and Testing Copper Chloride (photocopy at 108%) * 1 sheet of white paper * paper towels For each student * 1 pair of safety goggles 1 Student Sheet 24.1, Determining Concentration 1 Student Sheet 24.2, Treating Waste 1 Student Sheet 24.3, Diluting Used Copper Chloride Solution to 1 ppm Copper (optional) *Not supplied in kit B-138

3 Diluting the Problem Activity 24 Masters for Scoring Guides are in Teacher Resources III: Assessment. Masters for Science Skills sheets and literacy transparencies are in Teacher Resources II: Diverse Learners. When making a transparency and photocopies of Transparency 24.1, photocopy at 108% so that it fits directly under the wells of the SEPUP tray. If you would like students to place the copy under their SEPUP tray as they work, make enough photocopies for each pair of students. Pour equal amounts of used copper chloride solution from Activity 23, Producing Circuit Boards, into eight 30-mL dropper bottles labeled Used Copper Chloride Solution. Add 10 drops of red food coloring to a plastic cup that is half filled with water. Fill a second cup one quarter full of water. Set out a waste container labeled to collect copper chloride waste solutions from this activity. Students will use Student Sheet 24.2, Treating Waste again in Activities 26, 27, and 28. Decide on a place in the classroom where students can access the sheet easily or where they can keep them for use during these upcoming activities. SAFETY Have students wear protective eyewear during the activity. Solutions used in this activity, such as ammonia and the copper chloride waste solution, are toxic and corrosive. Avoid contact with skin and eyes. Wash with water for 2 3 minutes any area that comes in contact with the solution. If contact with an eye occurs, rinse eye for minutes, and consult a doctor. Disposal It is important that you dispose of the liquid waste generated in this activity and others in the unit in accordance with your local regulations. It contains copper, a regulated heavy metal, in concentrations of 1 100,000 parts per million (ppm). For more information, see the Safety section in Activity 23, Producing Circuit Boards. B-139

4 Activity 24 Diluting the Problem TEACHING SUMMARY Getting Started 1. Introduce the copper chloride waste problem. 2. Discuss what is meant when concentration is expressed in parts-per-million. Doing the Activity 3. Students perform a serial dilution of a copper chloride solution that has a known concentration. 4. Students determine the concentration of copper in the used copper chloride solution. Follow-Up 5. The class calculates copper concentration in the used copper chloride solution in parts per million and as a fraction. 6. The class discusses dilution as a treatment for the used copper chloride.if this wor BACKGROUND INFORMATION Copper and Health Small amounts of copper are essential to the lives of many kinds of organisms. In green plants copper is part of a molecule that plays a role in photosynthesis. In humans copper acts as a coenzyme for some metabolic processes. In larger amounts, however, copper is quite toxic. Although the exact amount of copper that can kill a human is not known, it is known that a level of 5 8 mg/1 kg of body weight can cause illness after ingestion. Levels of 40 mg/1 kg could possibly cause death. B-140

5 Diluting the Problem Activity 24 TEACHING SUGGESTIONS GETTING STARTED 1. Explain the copper chloride waste problem. Show students the copper chloride waste solution produced in Activity 23, Producing Circuit Boards. Explain that this is similar to the waste from actual circuit-board production. Remind them that the main components of the solution are water and copper-containing compounds formed when the copper-etching solution chemically reacted with the copper metal. Once the circuit board is etched, the copper chloride solution is left over, and manufacturers must decide how to handle the resulting waste. Ask students, What should we do with our used copper chloride solution? Encourage the class to brainstorm a list of options. Students answers will likely include pouring the solution down the drain and delivering the solution to a waste-collection site. Consider looking up with the class local limits for pouring copper-containing solutions down the drain. Explain that it might seem easiest to pour it down a sewer. But the harm to animals and humans when too much copper is released into the water systems is a health hazard. Like other toxic substances, the disposal of copper is regulated by laws that set limits on what wastes can be released into the environment. Tell students that while living things need copper in small amounts, in larger amounts copper can be toxic and is a problem too big to ignore. For more information of the effects of copper on health see the Background Information. In most places, the concentration of copper in wastewater cannot exceed 1 10 parts per million (ppm). Parts per million is a way to measure the concentration of one component compared to the amount of the whole mixture. This concept will be developed in Teaching Step 2 and further explored in Unit C, Water, of Issues and Physical Science. Explain to students that in this activity they will determine the concentration of copper chloride in the used copper chloride solution in parts per million (ppm). This will help them determine how much water it would take to dispose of the waste according to legal regulations. Point out that many units can communicate concentration, but partsper-million is often used when talking about substances for which a very small amount in a large volume is significant because the solution can still be toxic. 2. Discuss what is meant when concentration is expressed in parts per million. Talk with the class about ways in which concentrations are described. Students may be familiar with concentrations expressed in percentages, such as the 5% alcohol solution used in this activity. You might hold up a container of hydrogen peroxide or rubbing alcohol that shows the percent composition. Students may not be familiar with the concept of parts per million (ppm). Tell them that parts per million is a measurement that describes the amount, or concentration, of one substance in a mixture, as in one part copper in a solution of a million parts. In this activity student will determine the concentration of copper in a rinse-water solution. For students to effectively perform the serial dilution in the first part of this activity, they will need to understand the measurement of parts per million. Parts per million is the key concentration in this and subsequent activities since it describes substances that while very low in concentration, remain toxic to the health of humans and animals. To demonstrate parts per million show students a plastic cup containing red food coloring and water. Explain how you prepared this solution. Then pour half the solution into a second cup. Ask, What is the concentration of the solution in the second cup more, less, or the same as the first cup? The answer is that it is the same. Next add water to the second cup, and repeat the question, What is the concentration of the solution in the second cup more, less, or the same as the first cup? This time, the answer is less because when more water was added it lowered the amount of food coloring in water. This is a more dilute solution. Emphasize that adding more water, and making the amount of red food coloring in the cup dilutes the solution. The solution in the first cup is more B-141

6 Activity 24 Diluting the Problem concentrated, while the solution in the second cup is more dilute. Generally, if a solution is colored as with food coloring or tea the color becomes less visible as it becomes more dilute. Ask students, How could you make the solution in the second cup (or the first cup) more dilute? They may suggest adding more water, or removing some of the food coloring. Emphasize that both of these methods decrease the amount of food coloring per volume of water, or concentration. Understanding the concept of concentration will help them as they construct a serial dilution and determine how many parts per million of copper are in the waste solution from Activity 23, Producing Circuit Boards. DOING THE ACTIVITY 3. Students perform a serial dilution of a copper chloride solution that has a known concentration. Explain that a serial dilution is a way to approximate concentration of a substance. Let students know that they will take a substance of known concentration (100,000 ppm) and dilute it. Then they will compare this to the concentration of the used copper chloride from Activity 23, Producing Circuit Boards, to determine its concentration. Instruct students in the proper use of the dropper bottles as shown on Science Skills Transparency 2, Use of a Dropper Bottles. When SEPUP dropper bottles are held upside down and vertically, the bottles produce drops of consistent size, allowing for reproducible measurements. This is especially important when constructing a serial dilution, a tool that will assist students in determining concentration. Approximately drops from the SEPUP dropper bottles equals 1 ml. As a class read the introduction, Challenge, and review the Procedure. Point out that Cup 8 will contain water only, this is to be used as a control for comparison purposes. Assure that students understand the importance of cleaning the dropper in between cups so as not to unnecessarily add additional copper to any of the cups in the serial dilution. You may want to use Transparency 24.1, Diluting and Testing Used Copper Chloride, in reviewing the Procedure. Hand out Student Sheet 24.1, Determining Concentration. As the students work on the investigation, circulate around the classroom. Monitor and assist where needed, but encourage each pair of students to work as independently as possible. This activity requires students to read a scientific procedure. Encourage students to be independent as they read and complete the procedure. If you o bserve they need support, model the strategies on Literacy Transparency 3, Reading Scientific Procedures. Learning and practicing these skills will help students become more independent in laboratory activities and become stronger readers. 4. Students estimate the concentration of copper in the used copper chloride solution. In Part B of the Procedure students use the serial dilution they created in Part A with the solution of known concentration to estimate the unknown concentration of copper in the used copper chloride solution, from Activity 23, Producing Circuit Boards. Students will add ammonia to detect the presence of copper ions at a concentration greater than 100 ppm. When ammonia is mixed with the coppercontaining solutions, the ammonia initially forms a precipitate of milky-green copper hydroxide. As more ammonia is added, the precipitate dissolves and the solution turns blue, indicating the presence of the copper-ammonia ion. Seeing if this complex chemical reaction occurs is a more reliable test for detecting unsafe levels of copper than judging solution color alone. Constructing the serial dilution while using the ammonia indictor allows students to determine the concentration of the copper chloride waste. Typically students results after the serial dilution lead them to estimate the concentration of copper chloride in the waste solution to be approximately 50,000 ppm through 100,000 ppm. B-142

7 Diluting the Problem Activity 24 The equations for these reactions are as follows: Cu OH - Cu(OH) 2 (milky green precipitate) Cu(OH) 2 + 4NH 3 [Cu(NH 3 ) 4 ] OH - (blue ion) Teacher s Note: If in Procedure Step 10 adding 5 drops of ammonia to Cup 1 produces only a milkygreen precipitate, tell students to increase the number of drops one at a time until a blue color is obtained. If it takes more than 10 drops to produce the blue color, you should replace the ammonia with fresh ammonia. Sample student results are shown on the next page. Students will calculate the concentration for each of the cups during Teaching Step 4. After students have completed the lab, they should pour the waste solutions into the waste container you have provided and use their droppers to transfer any remaining liquid into the waste container as well. To ensure that no copper-containing wastes are washed down the drain, give students paper towels to wipe off remaining copper-containing solutions from trays and equipment before washing all equipment. FOLLOW-UP 5. The class calculates the copper concentration in the used copper chloride solutions in parts per million and as a fraction. Ask students to share the observations they recorded in their tables. Display Transparency 24.1, Diluting and Testing Used Copper Chloride, and point out the concentration of the solution in Cup 1 is 100,000 ppm as shown on the bottle. Next explain that 100,000 ppm is equivalent to the fraction 100,000/1,000,000. Write this value in the column titled As a fraction. Show how this fraction can be reduced, or simplified, to 1/10 by crossing out the same number of zeroes in the denominator and numerator. Write this value in the column titled As a simplified fraction on Student Sheet 24.1, Determining Concentration. Tell students that 1/10 is the same as one part in 10. Remind students that each cup was diluted with nine drops, or parts, water to one drop, or part, solution. This means that each cup was 1/10 as concentrated as the cup before it. You may wish to show Transparency 24.1, Diluting and Testing Copper Chloride, to review the Procedure. To determine the concentration in Cup 2 the denominator is increased by a factor of 10; do this by multiplying the denominator 10 (the concentration in Cup 1) by 10. The concentration in Cup 2 is 1/100, or one part in 100. Use optional Student Sheet 24.3, Diluting Used Copper Chloride Solution to 1 PPM Copper, to demonstrate this concentration. Concrete models, like one penny in a dime compared to one penny in 10 dimes, can help you explain this idea. It is important to point that this visual model may promote the misconception that not every part of a solution contains the substance in question. Be sure to emphasize that in a solution every drop contains some amount, even a minuscule amount, of the substance being measured; all of these amounts contribute to the total concentration of a substance in a solution. This concept will be developed further in Unit C, Water, of Issues and Physical Science. You may need to review with students how to convert 1/100 to 10,000/1,000,000. Then point out that 10,000/1,000,000 means 10,000 parts per million. Explain that many substances that people are concerned about in the environment (lead, copper, and mercury, for example) are present in relatively low amounts. If these concentrations were expressed as fractions, such as 10,000/1,000,000, it would cumbersome. Parts per million is clearer and simpler. B-143

8 Activity 24 Diluting the Problem Sample Student Results for Student Sheet 24.1, Determining Concentration Cup Copper chloride + water Color of solution Copper chloride + water + ammonia In parts per million (ppm) Concentration As a fraction As a simplified fraction 1 Green Milky green to blue 100, ,000 1,000, Light green Dark blue 10,000 3 Colorless Light blue 1,000 4 Colorless Slight blue tint Colorless Colorless 10 6 Colorless Colorless 1 10,000 1,000,000 1,000 1,000, ,000, ,000, ,000, , , , ,000,000 7 (Water) Colorless Colorless (Used copper chloride solution) Green Milky green to blue about 100, ,000 1,000, The class discusses dilution as a treatment for the used copper chloride. Project Transparency 24.2, Treating Waste Concept Map. Explain that in this activity students considered one way to treat the used copper chloride waste from Activity 23, Producing Circuit Boards dilution. In this, and in the next series of activities they will explore three more methods of dealing with the waste incineration, precipitation with solids, and precipitation with liquids. As a way to keep track of what they are learning about each method, and as a tool to help them with their final decision about how to treat the waste, they will record information about each method on Student Sheet 24.2, Treating Waste. As a class, fill out the Dilution column to summarize the treatment method. Sample student answers are shown on the next page. For Analysis Question 2, make sure that students have come to the understanding that toxic waste is not always visible in a solution when in low concentrations. This creates the need for a test like the ammonia test. It is possible that students will find a variety of ways to work through the calculations to answer Analysis Question 4. Allow them to explore different methods. If they need support, consider passing out optional Student Sheet 24.3, Diluting Used Copper Chloride Solution to 1 PPM Copper. If you decide to do so, be sure to explain that this dilution sequence is specific to a 100,000-ppm solution. It may help students understand the quantities of water described in Analysis Questions 4 and 5 if you express them in terms of the water needs for a family of four. Most families of four can get along comfortably on 1,000 liters (250 gallons) of water per day, not counting outdoor applications, such as watering the garden. You might display a 2-L soft drink bottle to help students imagine L containers being delivered to their houses each day to meet their basic water needs. At this level, a family of four uses approximately 30,000 liters (7,500 gallons) of water per month. That is equivalent to 15,000 2-liter bottles! To dilute one liter just one B-144

9 Diluting the Problem Activity 24 Sample Student Responses to Student Sheet 24.2, Treating Waste (Results for Dilution) Dilution Incineration Reclaim using solids Reclaim using liquids Summary of method Does it involve a chemical change? Positives Adding water to lower the concentration of waste in a solution No Easy to add water Can then release waste into water system Need a huge volume of water to reduce to nontoxic levels before can be put down drain Negatives Heavy metals, even if diluted, build up to unhealthy and toxic levels in waterways and harm ecosystems and humans liter of 100,000 ppm toxic waste to 1 ppm would require the same amount of water that the family of four uses in three months. The quantities of toxic copper chloride waste produced by various industrial processes are much greater than one liter we re talking about thousands and millions of liters. The amount of water needed to dilute only 100 liters of 100,000 ppm used copper chloride solution to a safe level of less than 1 ppm is the same as a family s water needs for over 27 years! That s a lot of water that a manufacturer would need in a short amount of time. This explanation can lead into a discussion of Analysis Question 6. Analysis Questions 5 and 6 turn students attention from determining the concentration of copper in a solution to using dilution as a disposal option for the copper-containing waste generated when manufacturing circuit boards. Use students answers to these questions to discuss with the class the option of diluting, and then pouring the used copper chloride solution down the drain. Encourage students to look up local guidelines for Analysis Question 6, as prompted in the extension, and to incorporate those into their answers. Students often think that dilution is an acceptable strategy for disposing of potentially toxic waste. Point out that a growing body of scientific evidence shows that dilution as a technique for dealing with solid, liquid, or gaseous wastes has had varying degrees of success. One important point for students to keep in mind is that, regardless of the concentration, the total amount of toxic waste released into an aquatic environment (stream, river, lake, or ocean) remains the same for heavy metal substances such as copper, mercury, and lead. Thus, even if the concentrations of the metals are minute when they are disposed of by dilution, they accumulate in ecosystems, eventually threatening humans and animals. Because the major goal of pollution prevention is to reduce the amount of toxic materials released into the environment, dilution is not usually an effective option for wastes that are particularly hazardous. Today, it is illegal to dispose of s above a certain concentration and volume by pouring them into drains, sewers, or bodies of water. In most areas, local water districts establish and enforce these standards, which limit the concentration of copper that can be deposited into the sewers from one source in a single day to 1 10 ppm. Many municipal wastewater treatment plants are not equipped to reduce the copper concentration low enough to be considered safe. B-145

10 Activity 24 Diluting the Problem EXTENSION The extension challenges students to find information about the local limits for copper disposal down the drain. Encourage them to contact local Enviornmental Protection Agencies, or school district officials to find this information. This information can be used to lead a class discussion on whether the used copper chlroide waste can be poured down the drain once it is diluted. SUGGESTED ANSWERS TO QUESTIONS 1. Which contains a more dilute solution, Cup 1 or Cup 2? Explain. The solution in Cup 2 is less concentrated because it is the 100,000 ppm copper chloride solution from Cup 1 with water added to dilute it. 2. Was there copper in Cups 1-6? How did you know it was or was not there? Explain, using evidence from this activity. When first observing the color of the solutions, it appeared that cups 1 and 2 were the only ones that had copper. Then, when the ammonia indicator was added, it showed that copper was present in cups 1, 2, 3, and What is the concentration of copper in the class s used copper chloride solution from Activity 23, Producing Circuit Boards? Use the evidence from the activity to support your answer. The concentration of the copper is about 100,000 ppm. I know this because the color of Cup 7 was closest to the color of Cup 1 when I added the ammonia indictor, and Cup 1 has a concentration of 100,000 ppm. 4. How many liters of water would you need to dilute 1 liter of used copper chloride solution from 100,000 ppm of copper to less than 1 ppm? It would take 99,999 liters of water to dilute 1 liter of the to less than 1 ppm. Answers to the optional Student Sheet 24.3, Diluting Used Copper Chloride Solution to 1 ppm Copper, are shown on the next page. 5. Based on your answers to Analysis Questions 3 and 4, how many liters of water would it take to dilute your waste from Activity 23, Producing Circuit Boards, to 1 ppm, an acceptable concentration to pour down the drain? According to the calculations in Analysis Questions 3 and 4, it would take 99,999 liters of water to dilute 1 liter of the copper waste solution to 1ppm. 6. Is dilution an acceptable way to dispose of the used copper chloride solution? It would take a lot of water to dilute a very little bit of waste. So it is not really feasible for a company that is producing circuit boards, unless they are willing to incorporate large volumes of water, which does not seem good for the environment either. Also, even though the amount of copper is smaller, relative to the amount of water when diluted, the copper will end up down line in the water system and may accumulate in another part, harming an ecosystem. B-146

11 Diluting the Problem Activity 24 Sample Answers to Student Sheet 24.3, Diluting Used Copper Chloride Solution to 1 ppm Copper 1 liter of 100,000 ppm + 9 liters of water = 10 liters of 10,000 ppm 10 liters of 10,000 ppm + 90 liters of water = 100 liters of 1,000 ppm 100 liters of 1,000 ppm liters of water = 1,000 liters of 100 ppm copper solution 1,000 liters of 100 ppm copper solution + 9,000 liters of water = 10,000 liters of 10 ppm copper solution 10,000 liters of 10 ppm copper solution + 90,000 liters of water = 100,000 liters of 1 ppm copper solution B-147

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13 2007 The Regents of the University of California Issues and Physical Science Transparency 24.1 B-149

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15 Treating Waste Concept Map Manufacturing processes produce Waste treatment options treatment options Disposal Reuse reclaim through Incineration Dilution Precipitation Metals Solutions 2007 The Regents of the University of California Issues and Physical Science Transparency 24.2 B-151

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17 Name Date Determining Concentration Color of Solution Concentration Cup Copper Chloride + Water Copper Chloride + Water + Ammonia In parts per million (ppm) As a fraction As a simplified fraction 1 100, The Regents of the University of California 7 (Water) 9 (Used copper chloride solution Issues and Physical Science Student Sheet 24.1 B-153

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19 Name Date Treating Waste 2007 The Regents of the University of California Dilution Incineration Reclaim using solids Reclaim using liquids Summary of method Does it involve a chemical reaction? Positives Negatives Issues and Physical Science Student Sheet 24.2 B-155

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21 Name Date Diluting Used Copper Chloride Solution to 1 ppm Copper 1 liter of 100,000 ppm + 9 liters of water = 10 liters of 10,000 ppm 10 liters of 10,000 ppm + 90 liters of water = 100 liters of ppm 100 liters of ppm + liters of water = liters of ppm liters of ppm + liters of water = liters of ppm 2007 The Regents of the University of California liters of ppm + liters of water = liters of 1 ppm Issues and Physical Science Student Sheet 24.3 B-157

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