Forming, Testing, and Modifying Hypotheses

Introduction

In this investigation you will:

1. make hypotheses concerning an observable event
2. perform an experiment that tests one hypothesis and collect data
3. examine the data and, if necessary, revise the hypothesis
   

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Observation

Examine the 2 test tubes without touching them. Record all similarities and differences on the data sheet provided.

Forming a Hypothesis

Based on your observations, form a hypothesis as to whether the 2 liquids are the same and record this on the data sheet.

Suggest experiment(s) that can be done safely and with the materials provided which will test your hypothesis.

Check these with your instructor to insure safety.

Experimentation

Perform all approved experiments, being sure to record all data on the data sheet.

Verify or modify your hypothesis after examining your data. Do you have enough information to verify your hypothesis? If you answer "yes", restate your hypothesis and record it on the data sheet.

If you have not performed the following set of experiments, do so now.

Experiment 1

With your thumb on the stoppers, give each test tube one hard shake and record your observations. Do you think they contain the same or different liquids? Record results and modified hypothesis, if any.

Experiment 2

Remove the liquid in the full test tube, pouring out just enough so that it has the same level as the liquid in the other tube. Restopper the tube. With your thumb on the stoppers, give each test tube one hard shake and record your observations. Do you think they contain the same or different liquids? Record results and modified hypothesis, if any.

Experiment 3

Refilling the test tubes is not permitted. What happens if you shake each tube from experiment 2 more than once? Design a systematic experiment to test this. Make a data chart and perform several trials. What is your modified hypothesis? On the basis of all of the experiments, can you determine whether the liquids are the same or different? Record results and modified hypothesis, if any.

Suggest a reason or reasons for all of your observations and results. Was your first hypothesis a result of guessing or experimentation? Was your final hypothesis the result of guessing or experimentation?

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Observations:

Similarities Differences

Initial Observations


Initial Hypothesis


Results Experiment 1


Modified Hypothesis, if any


Results Experiment 2


Modified Hypothesis, if any


Results Experiment 3


Modified Hypothesis, if any

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The unknown liquids are very dangerous. Wear eye protection and aprons at all times during the experiment. Be extremely careful when shaking the test tubes to shake them so that the tubes do not strike some other object and break. Wash spills immediately with large amounts of water. Do not ingest chemicals. Wash your hands after the experiments are complete.

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• Retain a test tube completely filled with the solution. You may loan this to students during experiment 3 and tell them that it is the same as the nearly filled tube they started with.
• Oxygen is a reactant in this system. Oxygen is reacting with glucose and with methylene blue. Shaking the solution with air dissolves oxygen which oxidizes the methylene blue. Upon standing, glucose reduces the oxygen and then the oxidized (blue form) methylene blue.

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• 2 13 x 100-mm test tubes, corks to fit (corks preferred to rubber stoppers)
• small beaker
• Prepare a solution containing:
• 300 mL distilled water
• 3 g NaOH
• 3 g glucose
• 3-5 drops 0.1% methylene blue (dissolve 0.1 g of methylene blue 100 mL of ethanol)
  
  • The solution will be blue when first made but will turn colorless upon standing. If the solution is not strongly blue, add more blue indicator.
• Before the class arrives, prepare pairs of tubes, one filled nearly all of the way and stoppered, the other one quarter or one fifth filled and stoppered.
  

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The microscale version of this lesson was developed by:

Evelyn S. Mitchell
Mercy High School
1501 S. 48th Street
Omaha,NE 68106

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