Name: _____________________________   Period: _____    Date: _____________

 

General Biology

Identifying Variables

 

Introduction: Scientists use the scientific method to learn about the natural world.  This process begins with observing a natural phenomena and wondering about it.  Then the scientist will make a hypothesis (testable explanation for the phenomena) and design an experiment to test that hypothesis.  Whenever possible, the experiment must be controlled.  In a controlled experiment, two groups are tested, the control group and the experimental group.  These groups are identical in every detail except one; in the experimental group, a single factor or variable is changed.  This variable is called the manipulated variable.  At the end of the experiment, the results of the experimental group are compared to the results of the control group.  The response that is measured as a result of the change in the manipulated variable is called the responding variable.

 

It is very important that is only one manipulated variable.  Otherwise you cannot be sure of what is causing the varying results seen in the experimental and control groups.

 

Purpose: The purpose is to determine the effect calcium chloride has on water temperature.

 

Materials:

Safety Goggles                                               Calcium chloride (CaCl2)                   

Thermometer                                                   Plastic measuring scoop         

4 identical size containers                               Graduated cylinder

 

Hypothesis: Write a hypothesis in the form of an Ifthen statement predicting what effect calcium chloride will have on water temperature.

 

 

 

 

 

 

 

Procedure:

  1. Put on your safety goggles.
  2. Label your small containers A, B and C if not already labeled.
  3. Add 75 ml of tap water to each container.
  4. With a thermometer, measure the temperature of the water in container A.  When doing this, be sure not to record a measurement until the reading on the thermometer stays constant.  Keep the thermometer in the water while reading it.  Leave it in the water.  Record the temperature in the trial one data table under Initial Temperature.
  5. Measure the temperature of the water in container B.  Record it in the trial one data table under initial temperature.
  6. Measure one level scoop of calcium chloride and add it to container B.  Stir with a stirring rod (not the thermometer) until all the calcium chloride has dissolved.  Hold the thermometer in place while stirring. 
  7. Measure the temperature of the water in Beaker B as soon as all the calcium chloride has dissolved.  Record the temperature in the trial one data table under final temperature.
  8. Calculate the change in temperature for container B and record it in the trial one data table. 
  9. Check the temperature of Beaker A again and record the reading in the trial one data table under final temperature.
  10. Measure the temperature of the water in container C.  Record it in the trial one data table under initial temperature.
  11. Measure three level scoops of calcium chloride and add them to container C.  Stir with a stirring rod (not the thermometer) until all the calcium chloride has dissolved.  Hold the thermometer in place while stirring. 
  12. Measure the temperature of the water in Beaker C as soon as all the calcium chloride has dissolved.  Record the temperature in the trial one data table under final temperature.
  13. Calculate the change in temperature for container C and record it in the trial one data table. 
  14. Calculate the temperature change for Beaker A and record it in the trial one data table.
  15. Dump the contents of all containers into the sink with running water.  Rinse out the cups, thermometers and stirring rods.
  16. Repeat the entire procedure again except this time record all your data in the trial two data table.
  17. Dump the contents of the cups in the sink with running water.  Rinse and dry all materials.
  18. Calculate the average temperature change for both containers from trial one and two and record this in the average data table

 

Data

Trial One

Container

Number of Scoops

Initial Temperature (C)

Final Temperature (C)

Change in Temperature (C)

A

0

 

 

 

B

1

 

 

 

C

3

 

 

 

 

Trial Two

Container

Number of Scoops

Initial Temperature (C)

Final Temperature (C)

Change in Temperature (C)

A

0

 

 

 

B

1

 

 

 

C

3

 

 

 

 

 

Average Change in Temperature

Container

Trial One Change in Temperature (C)

Trial Two Change in Temperature (C)

Average Change in Temperature (C)

A

 

 

 

B

 

 

 

C

 

 

 

 

Analysis: Identify the following parts of this experiment.

 

Experimental Group:____________________________________________________________

Control Group: ________________________________________________________________

Manipulated Variable: __________________________________________________________

Responding Variable: ___________________________________________________________

Constants: (give at least three things): ____________________________________________________________________________________________________________________________________________________________

 

Conclusion: Write a conclusion for this experiment.  Your conclusion should be a paragraph in complete sentences.  Include the following in the order listed below.

1.  Restate your original hypothesis.  Begin this sentence with; The original hypothesis was

2.  State whether the hypothesis was correct or incorrect. 

3.  Support this with averages from your last data table.

4. Experimental errors.

5. What further experiments would you do?

 

Conclusion:

 

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