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chemistry lab2
 Run No. Cup Temp. (˚C) Time (sec.) Observations 1 C RT H 2 C RT H 3 C RT H Avg. C RT H

Activity 2 Table

 State the hypothesis. Identify the independent variable. Identify the dependent variable. List the controlled variables. How will the dependent variable be measured? Describe the expected results if the hypothesis is true.

Data Table 2

 Run No. Manipulated Variable Time (sec.) Observations 1 2 3 Avg.

Faster Plop, Plop, Fizz, Fizz: A Scientific Method Investigation

Pre-laboratory Questions:

1. What are the independent and dependent variables?

2. Define at least three controlled variables.

3. State your hypothesis for today’s experiment as an “if/then” statement.

Activity 1 Questions:

1. Was the hypothesis proven or disproven?

2. Were the results reproducible?

3. What could have been done to make the results more reproducible?

4. What variable was not completely controlled during the experiment, and what could have been changed to make this variable more constant?

Activity 2 Questions:

1. List five questions about the rate at which Alka-Seltzer® tablets dissolve. Think about the controlled variables. What would happen if temperature were held constant and one of the controlled variables were changed?

2. Develop a new hypothesis based on one of the questions. Remember that a hypothesis must be testable with empirical or measurable data. Fill in Activity 2 Table.

LABORATORY QUESTIONS

1. Graph the results of Activity 1.

a. What are the two variables that will be graphed?

b. Which is the independent variable? Should it be on the X- or Y-axis? Why?

c. Which is the dependent variable? Should it be on the X- or Y-axis? Why?

2. Can a straight line be drawn through the graphed Activity 1data points? What conclusions can be deduced from the slope of the line?

3. Predict how long it will take to dissolve an Alka-Seltzer® tablet in 200 mL of water at:

d. 35°C

e. 60°C

f. 80°C

4. Was the hypothesis for Activity 2 proven or disproven?

5. If the hypothesis was proven, should the experiment be deemed a failure or a success? Why?

6. If the hypothesis was disproven, should the experiment be deemed a failure or a success? Why?

7. Based on your results for Activities 1 and 2, list two other hypotheses and experiments aimed at understanding the factors that influence the rate at which Alka-Seltzer® tablets dissolve.

8. Share your results with your classmates. Based on a collection of the different hypotheses, experiments, and results, what are the most important factors influencing the rate at which Alka-Seltzer® tablets dissolve?

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FASTER PLOP, PLOP, FIZZ, FIZZ

2 Overview 2 Objectives

· 2  Time Requirements

· 3  Background

· 6  Materials

· 7  Safety

7 Preparation 7 Activity 1

· 9  Activity 2

· 10  Disposal and Cleanup

Overview

The scienti c method is an approach to answering a question. Science is an evidence-based discipline that attempts to build a better understanding of the natural world and how it works. One of the primary tools of scienti c research is the use of the scienti c method to answer speci c questions. In this exercise, the scien- ti c method is used to investigate the rate at which e ervescent tablets dissolve in water and to identify the factors that a ect this rate. After an initial experiment, a question will be developed, and the scienti c method will be applied to answer it. The objective is to begin to understand the scienti c method and to learn how to collect and analyze data.

Objectives

• Formulate a hypothesis that can be tested empirically, i.e., based on observation.

· Explain independent, dependent, and controlled variables and how to apply them in designing an experiment.

· Apply key principles of the scienti c method in designing an experiment to answer a question.

· Analyze data generated by the experiment to determine whether it supports or refutes the hypothesis.  Time Requirements  Preparation ………………………………………………………….. 15 minutes Activity 1: Temperature vs. Time to Dissolve……………… 40 minutes Activity 2: Testing the New Hypothesis …………………….. 40 minutes  Key  Personal protective equipment  (PPE) goggles gloves apron

video submit warning corrosion ammable toxic environment health hazard

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Background

In our day-to-day experience, we all make observations about how the world works. In the fall, the leaves on trees change color. In the springtime, pansies are one of the rst owers to bloom. Sometimes these observations stimulate our curiosity. Why are pansies one of the rst owers to bloom each year? What characteristics of pansies are responsible for their early blooming? Are there ways that pansies can be pushed to bloom even earlier?

The goal of scienti c research is to try to understand these phenomena at a deeper level by asking questions. Science is an evidence- based discipline that attempts to build a better understanding of the natural world and how it works. One of the primary tools of scienti c research is the use of the scienti c method to answer speci c questions.

The scientific method involves doing experiments and making observations to answer a question of interest. The question generally arises from an observation such as “Why do leaves change color?” or “Why are pansies one of the rst owers to bloom each year?” or “Why do apples turn brown after they are cut?”

While there are many approaches to answering a question, the scientific method takes a distinctive approach. First, the question must

Figure 1.

be testable. A testable question is one for which empirical, or measurable, data can be collected to answer the question or provide insight. Another important component of testability is reproducibility. The empirical or measurable data must always yield the same results under identical conditions.

The scientific method can be used either to investigate an observed phenomenon or to design an experiment to test a hypothesis. A hypothesis is an educated assumption or prediction of what one expects to observe, or the predicted results of an experiment. The investigator integrates previous knowledge

in developing the hypothesis, and acquires new knowledge in the process of testing the hypothesis. The new knowledge gained can either support or refute the hypothesis. However, if the data collected are inconsistent with previous ndings, and if these new observations or data are reliably reproduced by other investigators, the existing broad scienti c understanding or theory may have to be revised and potentially discarded. Science has a built-in mechanism for self-correction, as justi ed by new evidence, to more accurately re ect reality.

The overall process followed in the scienti c method is represented in Figure 1.

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FASTER PLOP, PLOP, FIZZ, FIZZ

Background continued

Some people mistakenly believe that humans know everything there is to know about nature and natural processes, and that this knowledge is all-encompassing. Nothing could be further from the truth! In scienti c research, questions are answered based on experimental evidence; however, new questions are also raised. This is true in all branches of natural science. Scientists will continue to seek answers to new questions and to develop technologies to address both new questions and those that might have been unanswerable with earlier technologies.

Factors relevant to the question being asked are called variables. In designing a scienti c experiment, only one factor, or variable, is changed at a given time. There are three di erent kinds of variables involved in an experiment. The independent variable is the factor hypothesized to produce the e ect under investigation. This variable can be measured and is often controlled by the investigator. Some common independent variables are time, temperature, concentration, pH, and pressure.

Dependent variables are also measurable, but their values are dependent on the independent variables; i.e., the behavior of the dependent variable is based on the status of the independent variable. An easy way to think about the independent and dependent variables is the following statement, “If I change the independent variable from X to Y, what

will happen to the dependent variable?” A scientist will control the rate of change of the independent variable and observe the resulting change in the dependent variable.

The third type of variable is a controlled variable. Controlled variables are all other, nonindependent and nondependent variables, and they should remain unchanged while the independent variable is manipulated.

A real-world example of a phenomenon that an environmental scientist may investigate is the impact of algal blooms on a specific species of sh. Environmental scientists know, based on previous research, that algal blooms decrease the oxygen level in the water. The testable hypothesis that may be proposed is “Lower oxygen levels in water cause increased heart rate in sh.” The scientist hypothesizes that, at lower oxygen levels in the water, the heart rate of the sh would increase. If true, this might explain the mechanism that leads to stress or death in the sh population associated with algal blooms.

In the experiment, the oxygen level (independent variable) can be manipulated and the resulting heart rate of the sh (dependent variable) can be measured. In order to make this

study meaningful and reproducible, all other (controlled) variables must remain constant. For example, if the oxygen level and temperature were simultaneously manipulated, the scientist would not know which variable led to the change in the heart rate. Some examples of controlled variables in this experiment include water temperature, water pH, and light level. The experimental design must be able to accommodate these different kinds of variables so that all relevant controlled variables are held constant while the independent and dependent

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variables are manipulated and measured, respectively.

When the experiment is run and repeated to assess reproducibility, the hypothesis can be supported or not supported. More questions will likely be generated based on the analysis of the experimental data. Subsequent experiments will ask new questions and the hypothesis will be re ned until an understanding is achieved of whether reduced oxygen level is associated with increased heart rate in sh and, ultimately, of the impact on sh of all factors associated with an algal bloom.

In this lab activity, the scienti c method will be used to answer a much simpler question: “How fast does an Alka-Seltzer® tablet dissolve in water at different temperatures?” A hypothesis will be developed and tested. The experiment will then be repeated to determine whether the result is reproducible. After the rst activity, a second hypothesis will be developed for another variable. A test protocol will be developed and the second hypothesis will be tested.

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FASTER PLOP, PLOP, FIZZ, FIZZ

Materials

Included in the materials kit:

Alka-Seltzer® tablets, 5 packs

Needed from the equipment kit:

Beaker, 250 mL Thermometer Wax pencil

Needed but not supplied:

• 3 clear, plastic cups

· Medium-sized bowl or glass to make an  ice-water bath

· Hot tap water

· Stopwatch, kitchen timer, or cell phone with  stopwatch application (capable of measuring  to the nearest 0.1 second)

· Sharp knife, scalpel, or scissors

Reorder Information: Replacement investigation kit for Faster Plop, Plop, Fizz, Fizz: A Scientific Method Investigation, item number 580102, can be ordered from Carolina Biological Supply Company.

Call 800-334-5551 to order.

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Safety

Safety goggles should be worn at all times during this investigation.

Read all instructions for this laboratory activity before beginning. Follow the instructions closely and observe established laboratory safety practices, including use of appropriate personal protective equipment (PPE) described in the Safety and Procedure sections.

The Alka-Seltzer® in this kit is not for human consumption. The packages have not been kept in a food-grade facility and may be contaminated. Consider the tablet a laboratory chemical and not an over-the-counter pharmaceutical. Alka-Seltzer® contains aspirin and should be kept out of reach of children and pets.

Do not eat, drink, or chew gum while performing this activity. Wash your hands with soap and water before and after performing the activity. Clean up the work area and all glassware

with soap and water after completing the investigation. Keep pets and children away from lab materials and equipment.

Preparation

1. Read through the activities. 2. Obtain all materials. 3. Clean and sanitize work area.

ACTIVITY ACTIVITY 1

A Temperature vs. Time to Dissolve Part I. Setting Up the Experiment

Three different temperature baths will be prepared with approximately the same amount of water in each. Ideally, there should be about 40–50 °C difference between the cold and hot temperatures.

1. Label three cups C (for cold), H (for hot), and RT (for room temperature) using the wax pencil.

2. Obtain a timing device such as a cell phone or stopwatch.

3. Make an ice bath by adding ice and at least 400 mL cold water to a bowl or cup (there will need to be enough water/ice to make a nal volume of at least 600 mL).

4. Open the Alka-Seltzer® packages.

5. Carefully break/cut each Alka-Seltzer® tablet  into two EQUAL halves.

Tip: To break the Alka-Seltzer® tablets into equal portions, take a sharp knife, scalpel, or scissors and lightly score a line across the back of the tablet. Repeat this process several times along the same line. Using light pressure, break the tablet in half along the line. If your tablets have been broken

in shipping, try to create three equal-sized pieces for one of your trials and note the size variance on your data table.

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ACTIVITY ACTIVITY 1 continued

6. Use the 250-mL beaker to measure 200 mL of room temperature tap water and pour it in the “RT” cup.

7. Use the 250-mL beaker to measure 200 mL of hot tap water and pour it in the “H” cup.

8. Use the 250-mL beaker to measure 200 mL of ice-cold water from the ice water bath and pour it in the “C” cup (do not include any ice in the “C” cup).

9. Use the thermometer to measure the temperature of water in each of the three cups. Record these temperatures in Data Table 1.

Data Table 1.

Part II. Running the Experiment 1. Carefully drop half of an Alka-Seltzer® tablet

into each cup, starting with the “C” cup, followed by the “RT” cup, and then the “H” cup.

2. Immediately start the timer.

3. Observe the Alka-Seltzer® tablets as they  begin to dissolve in each cup.

4. When the last piece of tablet disappears, record the time to the nearest second for that cup in Data Table 1 (Run No. 1).

 Run No. Cup Temp. ( ̊C) Time (sec.) Observations 1 C RT H 2 C RT H 3 C RT H Avg. C RT H

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5. Pour the Alka-Seltzer® solution from each cup down the drain, and rinse out the cups with clean water.

Part III. Repeating the Experiment 1. Repeat Part II for two additional trials at each

temperature. Use exactly 200 mL of water in each cup.

2. For each temperature range, calculate the average temperature and record this in Data Table 1.

Data Table 2.

ACTIVITY 2

A Testing the New Hypothesis

Preparation 1. List ve factors that can potentially change

the rate at which Alka-Seltzer® tablets dissolve (other than temperature). Think about the controlled variables in the initial experiment. In other words, what would happen if temperature were held constant and one of the controlled variables was changed?

2. Develop a new hypothesis based on one of the ve factors listed in Question 1. Remember that a hypothesis must be testable with empirical, or measurable, data. Fill in Data Table 2.

The tablet will normally be floating near the top of the water by the end of the reaction.

 State the hypothesis. Identify the independent variable. Identify the dependent variable. List the controlled variables. How will the dependent variable be measured? Describe the expected results if the hypothesis is true.

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ACTIVITY ACTIVITY 2 continued

Testing the New Hypothesis for a “manipulated variable” will be lled out 1. To test your hypothesis, design a procedure (as needed) for the factor that was changed in

similar to the test procedure in Activity 1, but the new experiment.

keep the temperature constant and change a di erent variable to analyze the dissolving rate of Alka-Seltzer®. The test procedure should be described so another person

can repeat it exactly as it will be performed here. Be speci c and detailed in writing the procedure. Provide a materials list and descriptions for setting up and running the experiment, including a description of how data will be collected. Also describe repeating the experiment to determine reproducibility of the results. In Data Table 3 an extra column

Data Table 3.

2. Perform your experiment and record the results in Data Table 3.

Disposal and Cleanup

1. Dispose of all solid waste generated during the activity in the household trash.

2. Discard liquid waste in the sink.

3. Rinse out all cups and equipment used in the experiment in the sink. Clean and dry work area.

 Run No. Manipulated Variable Time (sec.) Observations 1 2 3 Avg.

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NOTES

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BIOLOGY Faster Plop, Plop, Fizz, Fizz: A Scienti c Method Investigation Investigation Manual

www.carolina.com/distancelearning 866.332.4478

Carolina Biological Supply Company

www.carolina.com • 800.334.5551