Chapter 1, Section 3
The Scientific Method
A Nobel Prize winner in science once said that science is about “ordinary people doing ordinary things.” Scientists have a powerful tool that they can use to produce valuable, sometimes spectacular, results. Like all scientists, the biochemist shown in Figure 1.18 is using the scientific method to solve difficult problems. The scientific method is a logical, systematic approach to the solution of a scientific problem. Steps in the scientific method include making observations, testing hypotheses, and developing theories. Figure 1.19 shows how these steps fit together.
Figure 1.18 Observation is an essential step in the scientific method.
Making Observations
The scientific method is useful for solving many kinds of problems because it is closely related to ordinary common sense. Suppose you try to turn on a flashlight and you notice that it does not light. When you use your senses to obtain information, you make an observation. An observation can lead to a question: What’s wrong with the flashlight?
Testing Hypotheses
If you guess that the batteries are dead, you are making a hypothesis. A hypothesis is a proposed explanation for an observation. You can test your hypothesis by putting new batteries in the flashlight. If the flashlight lights, you can be fairly certain that your hypothesis is true. What if the flashlight does not work after you replace the batteries? A hypothesis is useful only if it accounts for what is actually observed. When experimental data does not fit a hypothesis, the hypothesis must be changed. A new hypothesis might be that the light bulb is burnt out. You can replace the bulb to test this hypothesis.
Replacing the bulb is an experiment, a procedure that is used to test a hypothesis. When you design experiments, you deal with variables, or factors that can change. The variable that you change during an experiment is the manipulated variable, or independent variable. The variable that is observed during the experiment is the responding variable, or dependent variable. If you keep other factors that can affect the experiment from changing during the experiment, you can relate any change in the responding variable to changes in the manipulated variable.
For the results of an experiment to be accepted, the experiment must produce the same result no matter how many times it is repeated, or by whom. This is why scientists are expected to publish a description of their procedures along with their results.
Experiment contains the Latin root peri, meaning “to try or test.” The words expert and experience contain the same root. How could experiments provide the experience for someone to become an expert?
Bubbles!
Purpose
To test the hypothesis that bubble making can be affected by adding sugar or salt to a bubble-blowing mixture.
Materials
3 plastic drinking cups
liquid dish detergent
measuring cup and spoons
water
table sugar
table salt
drinking straw
Procedure
Label three drinking cups 1, 2, and 3. Measure and add one teaspoon of liquid dish detergent to each cup. Use the measuring cup to add two thirds of a cup of water to each drinking cup. Then swirl the cups to form a clear mixture. CAUTION Wipe up any spills immediately so that no one will slip and fall.
Add a half teaspoon of table sugar to cup 2 and a half teaspoon of table salt to cup 3. Swirl each cup for one minute.
Dip the drinking straw into cup 1, remove it, and blow gently into the straw to make the largest bubble you can. Practice making bubbles until you feel you have reasonable control over your bubble production.
Repeat Step 3 with the mixtures in cups 2 and 3.
Analyze and Conclude
Did you observe any differences in your ability to produce bubbles using the mixtures in cup 1 and cup 2?
Did you observe any differences in your ability to produce bubbles using the mixtures in cup 1 and cup 3?
What can you conclude about the effects of table sugar and table salt on your ability to produce bubbles?
Propose another hypothesis related to bubble making and design an experiment to test your hypothesis.
Developing Theories
Once a hypothesis meets the test of repeated experimentation, it may be raised to a higher level of ideas. It may become a theory. A theory is a well-tested explanation for a broad set of observations. In chemistry, one theory addresses the fundamental structure of matter. This theory is very useful because it helps you form mental pictures of objects that you cannot see. Other theories allow you to predict the behavior of matter.
When scientists say that a theory can never be proved, they are not saying that a theory is unreliable. They are simply leaving open the possibility that a theory may need to be changed at some point in the future to explain new observations or experimental results.
Scientific Laws
Figure 1.19 shows how scientific experiments can lead to laws as well as theories. A scientific law is a concise statement that summarizes the results of many observations and experiments. In Chapter 14, you will study laws that describe how gases behave. One law describes the relationship between the volume of a gas in a container and its temperature. If all other variables are kept constant, the volume of the gas increases as the temperature increases. The law doesn’t try to explain the relationship it describes. That explanation requires a theory.
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