Materials Included In Kit

Additional Materials Required

Safety Precautions

Copper(II) sulfate is moderately toxic by ingestion and inhalation and is a skin and respiratory irritant; avoid all body tissue contact. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

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. Many states regulate or limit the amount of copper(II) salts that may be disposed of down the drain with excess water. See the Lab Hints section for recycling options. Copper sulfate solutions from Experiment 2 may also be disposed of according to Flinn Suggested Disposal Method #26b and leftover solid copper(II) sulfate may be stored for future use or disposed of according to Flinn Suggested Disposal Method #26a.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Each separate experiment can be completed in one 50-minute class period. Additional time may be needed for the pre-laboratory observations and experimental design, and the data compilation and calculations may be completed the day after the lab.
• Observations of the cups in Experiment 1 may include researching the different types of material online, using hand lenses and flashlights and making quantitative measurements with rulers, calipers, balances and graduated cylinders.
• For Experiment 1, student pairs may combine into groups of four, using two thermometers for each set of four cups in order to measure the temperature more efficiently.
• Digital thermometers are recommended for Experiment 1. If spirit-filled thermometers are used, increase the length of time in order to observe more measurable differences among the cups. Experiment 1 is also well suited as an introductory technology-based experiment using temperature sensors.
• The amount of guidance given for the student-designed experiment is entirely up to the instructor. To simplify the type of materials needed, you may want to have all the student groups test the variable of particle size and then compare the reliability of their experimental designs and results.
• Sample data for Experiment 2 is based on adding 2 g of each solute to 100 mL of tap water in 250-mL beakers and stirring each at a constant rate. Another method would be to place the solute in a test tube, slowly add water to avoid mixing and seal the tube with a stopper. The test tube is then turned upside-down and back upright, counting the number of inversion cycles until all the solute is dissolved.
• Many states regulate or limit the amount of copper(II) salts that may be disposed of down the drain with excess water. Always check with your local or state agencies before disposing of any substances down the drain. Copper(II) ions may be precipitated as insoluble copper phosphate for disposal method # 26a, disposal of a solid in a landfill. Please call or write Flinn Scientific to request a free copy of Precipitation of Aqueous Copper Compounds, Publication No. 10870.
• The copper(II) sulfate solutions may be combined and recycled for future use in qualitative experiments involving chemical reactions or spectroscopy where the concentration is not critical. Examples include single and double replacement reactions. Once all of the solid has dissolved in each student-run investigation, the nominal concentration of CuSO₄ is 0.08 M. Note that the copper(II) sulfate provided in the kit is the pentahydrate, CuSO₄•5H₂O, molar mass 249.55 g/mole.

Teacher Tips

• This activity is suitable for introducing, practicing, and reviewing the scientific method in any science curricular area.
• For more practice in graphing skills, consider having students make a line graph of the data from Experiment #1.
• As an introductory demonstration of the scientific method, use A Reaction in a Bag, Flinn Catalog No. AP6607. After observing a chemical reaction, students are challenged to design controlled experiments to identify the substances responsible for each of the changes they observed.

Answers to Prelab Questions

Experiment 1

1. Observe each cup carefully and record as many observations as possible about each one. Include similarities and differences among the cups. Note: Check with your instructor to see if you may use any other equipment for your observations.
   

   Qualitative observations may include a description of the color and transparency or opacity of the cups, relative pliability, any markings and variations in shape, texture, etc. Quantitative observations may include height, top and bottom diameters, thickness, volume capacity and mass.

2. Based on the observations of the four different types of cups, write a hypothesis about which cup will keep a cold liquid (water) cold the longest (e.g., Cold water in the X cup will increase in temperature the least over time because…).
   

   Accept all reasonable hypotheses.

3. Read through the Procedure. Identify and record the independent variable and the dependent variable.
   

   The independent variable is the type of cup and the dependent variable is the change in the temperature of the water over time.

Sample Data

Experiment 1

Experiment 2

Answers to Questions

1. Write a conclusion based on the data gathered from the experiment. Include a summary of the results and whether or not your hypothesis was supported by the data. For example, a conclusion may begin in the following manner. “Cold water in cup X increased in temperature the least over a 9-minute period, which supported our hypothesis.”
   

   The water in the foamed polystyrene cup (D) increased in temperature the least over a 9-minute period, only 1.4 °C. The temperature of the water in cups A–C increased 2.4, 2.3 and 2.2 °C, respectively. These results support our hypothesis.

2. List the variables other than the cup material that may have affected the outcome of this experiment.
   

   Variables include the capacity, shape, and dimensions of the cups, the surface area of the water exposed to the air and the surface area of the water in contact with the cup, temperature of the air in the room, air convection/currents in the room, surface on which the cups are placed, initial temperature in each cup, time interval for temperature measurements, length of time thermometer remained in each cup, depth of thermometer when temperature was taken, stirring of water, amount of water in each cup, amount of light in the room, etc.

3. Were any of the variables listed in question 2 not controlled? In other words, were some of the variables different for some or all of the cups? Explain how the uncontrolled variables may be possible sources of error in this experiment.
   

   The capacity, exact shape, and dimensions of the cups were different, which resulted in different surface areas and depth of the water. This could affect the evaporation rate of the water and the rate of heat transfer. The time interval between measurements was not always exactly 1 minute, nor was the total time exactly 9 minutes for each cup.

4. How could the procedure be improved to better control all the variables and increase the reliability of the data?
   

   The dimensions of the cups cannot be changed. However, consumer tests usually compare products as they are normally used. Covering the cups with the same material (e.g., clear plastic wrap) and making a hole for the thermometer may help control any effects of air currents or evaporation. Using four thermometers instead of one or two and assigning one person to each cup may help gain consistency in the time interval between measurements. Using longer time intervals may also help. Staggering the filling and start time for each cup could help ensure the same initial temperature.

Discussion

This kit contains two experiments that will give students practice using the scientific method. The first experiment is a consumer product-testing lab in which the insulating ability of cold beverage cups will be tested and the second is a solubility lab in which factors affecting the rate at which a salt dissolves in water will be tested. The two experiments are independent of each other and need not be performed in any particular order. You may choose to do only one of the experiments. On the other hand, you may choose to do both, using the first one as an introductory activity and the other as a guided-inquiry activity.

Experiment 1 uses a standard procedure lab handout and student worksheet. This is a good option if time or materials are more limited. Since each group will perform the same procedure, graphing instruction and overall evaluation will be easier and more straightforward. If students perform this procedure, stress to them that this is not necessarily the “right” way or the best way to run the experiment. There may be many valid procedures and this is just the one that was chosen. Students have the opportunity to use their critical thinking skills to evaluate the experimental design.

Experiment 2 is an open-ended and inquiry-based option since students perform the actual experiment they design. This option may require additional materials according to the students’ requests. Note: You may give students some guidelines or restrictions on materials they may use. The student-designed procedure option will most likely require more time since each group performs a different experiment. Results and graphs will be very different so evaluation will need to be more individualized.

References

Consumer Reports. Product Testing Activities; Prentice-Hall: Englewood Cliffs, NJ, 1993; pp 6–4 to 6–5.

Cothron, J. H.; Giese, R. N.; Rezba, R. J. Students and Research; Kendall Hunt: Dubuque, IA, 1989; pp 3–9.

LeMay, H. E.; Beall, H.; Robblee, K. M.; Brower, D. C. Chemistry: Connections to Our Changing World; Prentice-Hall: Englewood Cliffs, NJ, 1996; pp 7–13.

Introduction

The natural world is filled with problems that need to be solved and phenomena that are puzzling. Scientists attempt to investigate the natural world in search of explanations. Science is the field of study that aims to provide explanations and answers to the many questions we have about our world.

Concepts

• Scientific method
• Hypothesis
• Independent/dependent variables

Background

The scientific method is a way of solving problems using a systematic approach. An organized strategy, such as the scientific method, is an effective way of approaching a problem. A wide variety of strategies may be implemented and the following is a list of steps that scientists may use to solve a problem.

Typical Steps in the Scientific Method

1. Define a problem or ask a question—A clear statement of the problem or question is a crucial step in beginning an investigation.
2. Make observations about the problem—All possible information on the problem will be helpful in writing a plausible hypothesis and in designing a good experiment.
3. Develop a hypothesis—This is a possible answer or tentative explanation to the problem or question. It should be based on the facts and observations and should be capable of being tested.
4. Design and carry out an experiment—Experimental testing will provide evidence that either supports or contradicts the hypothesis. Several factors must be determined before conducting an experiment.

Variables: The factors that influence the outcome of an experiment.
Constants: All other factors, except the one whose effect is being studied, that remain the same throughout an experiment.
Independent Variable: The variable that is intentionally changed or manipulated by the experimenter.
I The variable that is measured or watched, also called the outcome or the responding variable.

5. Record and analyze data—Data, such as observations and measurements, are recorded and then analyzed. If the data support the hypothesis, then the conclusion would state that the hypothesis is correct. If the data contradict the hypothesis, then a new hypothesis must be developed and tested.
6. Draw a conclusion—Scientists base their conclusions on observations made during experimentation.

Keep in mind, however, that although the above list of steps may be a “typical” approach, the strategy and the order of steps may vary greatly from problem to problem.

Experiment Overview

Two experiments will be conducted. The purpose of the first experiment is to find which type of beverage cup keeps cold water cold the longest. All student groups will follow the same standard procedure and evaluate the reliability of the test results. The purpose of the second experiment is to investigate variables that may affect the rate at which a solid dissolves in a liquid. For this investigation, each student group will design, conduct and evaluate its own teacher-approved experiment.

Experiment 1
Which cup is able to keep a cold liquid cold the longest?

Problem: Does the composition of a cup affect its insulating ability with respect to keeping a cold liquid cold? Four types of beverage cups are provided for evaluation—wax-covered paper, PETE (polyethylene terephthalate) plastic, clear PS (polystyrene) plastic and foamed PS plastic. Each student group will conduct the same standard procedure, which is just one possible way to determine the answer to the problem.

Experiment 2
What factors affect the solubility rate of a solid in a liquid?

Solubility is the maximum amount of solute that will dissolve in a given amount of solvent at a specific temperature. Although the overall solubility may be constant, the rate at which a solid dissolves in a liquid depends on many variables, such as temperature of the solvent, particle size of the solute, stirring and amount of solute already dissolved.

Problem: How do certain factors affect how fast a solid will dissolve in a liquid (the solubility rate)? Choose one variable (such as temperature, particle size, stirring, or amount of solute already dissolved) and design an experiment, using common laboratory materials, to test how that factor affects the solubility rate of copper(II) sulfate in tap water.

Materials

Prelab Questions

Experiment 1

1. Observe each cup carefully and record as many observations as possible about each one. Include similarities and differences among the cups. Note: Check with your instructor to see if you may use any other equipment for your observations.
2. Based on the observations of the four different types of cups, write a hypothesis about which cup will keep a cold liquid (water) cold the longest (e.g., Cold water in the X cup will increase in temperature the least over time because…).
3. Read through the Procedure. Identify and record the independent variable and the dependent variable.

Experiment 2

Observations
On a separate sheet of paper, record as many observations as possible about the samples of copper(II) sulfate provided by the instructor and other materials to be used.

Hypothesis
Based on the observations of the copper(II) sulfate and other materials, determine the independent variable and dependent variable for your experiment. Write a hypothesis that may be tested by your experiment on the same paper as your observations.

Safety Precautions

The materials in this lab are considered nonhazardous. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Experiment 1

1. Label each of the four cups A–D with a permanent marker as listed.

A = Wax-covered paper
B = PETE
C = Clear PS
D = Foamed PS

2. Fill a 1-L beaker or pitcher with 800 mL of cold tap water.
3. Using a spoon, add 6–8 ice cubes to the water and stir until the temperature has reached approximately 12 °C.
4. Remove any remaining ice from the cold water.
5. Measure and pour 200 mL of cold water into each of the four cups.
6. Measure and record the initial temperature of the water in each cup to the nearest 0.1 degree Celsius. Use the data table on the Scientific Method Worksheet.
7. Start the timer.
8. After 1 minute, gently stir the water in the first cup twice and then measure and record the temperature of the water in the cup. Do the same for the other three cups.
9. Repeat step 8 each minute for a total of 9 minutes.
10. For each cup, subtract the initial temperature from the final temperature to determine the overall change in temperature (ΔT). Record the difference in temperature in the data table.
11. Construct a bar graph of ΔT with the independent variable on the x-axis and the dependent variable on the y-axis. Attach the bar graph to the completed worksheet.

Experiment 2

Experimental Design

For an experiment to be considered valid, it must meet two important requirements:

a. Only one variable is tested at one time and it is the only one that will produce the observed results.
b. It is designed in such a way that any other scientists can repeat the experiment and get similar results.

1. Independent variable: State the factor that will be changed.
2. Dependent variable: State the factor that will be measured.
3. Materials list: Write a specific list of all materials needed, including sizes, amounts, etc.
4. Procedure: Write a clear, specific, step-by-step, repeatable procedure.
5. Safety precautions: A list of materials or procedures with any safety concerns that must be followed to ensure the well-being of everyone in the classroom. Include all personal protective equipment needed.
6. Diagram: Draw a rough sketch of the experiment.
7. Data Table: Construct an empty data table where results from this experiment are to be written. Clearly label all data columns. Include units where necessary. Leave space to write data for three trials and leave a column for averages.

Submit your experimental design to the instructor for approval.

Experimental Procedure

1. Once the group’s experimental design has been approved, gather the materials needed to perform the experiment.
2. Conduct your student-designed experiment. Note: During any experiment, it is good practice to record if and where any errors or inconsistencies may have occurred and the source of the error (e.g., human error, limitation of equipment, uncontrolled variable).
3. Record your data in the student-designed data table.
4. Repeat the experiment two more times and average the results.

Anaylsis

On a separate sheet of graph paper, construct a graph of the averaged data. Note: The independent variable should be plotted on the x-axis and the dependent variable on the y-axis. Label the axes with the variables and the units as needed.

Conclusion

Write a conclusion based on the data gathered from the experiment. Include a summary of the results and whether or not your hypothesis was supported by the data. Also include the possible sources of error in this experiment and describe ways that the procedure may be improved to give more reliable data.

Student Worksheet PDF

12784_Student1.pdf