High School Chemistry/How Scientists Use Data

In the last section, we learned a little more about making quantitative and qualitative observations. A set of observations about a particular phenomenon is called data. Scientist use many techniques to analyze and interpret data. Data analysis produces organized data that is more conducive to seeing regularities and drawing conclusions. Making tables and graphs of data are two of the most useful techniques in data analysis.

Lesson Objectives

 * Define the terms law, hypothesis, and theory.
 * Explain why scientists use models.

Natural Laws are Statements of Repeated Data Patterns
Around the year 1800, Jacques Charles and other scientists were working with gases to, among other reasons, improve the design of the hot air balloon. These scientists found, after many, many tests, that patterns and regularities existed in the observations on gas behavior. If the temperature of the gas increased, the volume of the gas increased. This is known as a natural law. A natural law is a relationship that exists between variables in a group of data. Natural laws describe the patterns we see in large amounts of data. These laws have withstood the test of time because they have been based on repeated observation with no known exceptions.

Around the same time as Charles was working with hot air balloons, another scientist, names J.W. Henry was doing experiments trying to find a pattern between the pressure of a gas and the amount of the gas that dissolved in water. Henry found that when one of these variables increased, the other variable increased in the same proportion. Have you ever gone scuba diving (Figure 3.2)? Scuba Divers learn about a problem known as "the Bends" when they are being trained. As scuba divers dive deeper, the increased pressure of the breathing air causes more nitrogen to be dissolved in the diver's blood. Coming up too quickly from a dive causes the pressure to decrease rapidly and therefore, the nitrogen to leave the blood quickly which leads to "the Bends". Henry's Law is called a natural law because it indicates a relationship (regularity) between gas pressure and the amount of dissolved nitrogen.



A Hypothesis is a Tentative Explanation
When scientists develop a description of the nature of matter to explain observations (including natural laws), the first attempt at an explanation is often referred to as a hypothesis. A hypothesis is your educated or best guess as to the nature of matter that causes those observations. The requirements for a hypothesis are only that the hypothesis explains all the observations and that it is not possible to make an observation that will refute the hypothesis.

The hypothesis must be testable. The test of a hypothesis is called an experiment. If the results of the experiment contradict the hypothesis, the hypothesis is rejected and a new hypothesis is formulated. The results of the experiment are now included in the observations list and the new hypothesis must explain this new observation as well as all the previous observations. If the result of the experiment supports the hypothesis, more tests are still required. Hypotheses are not proven by testing… they are merely supported or contradicted.

A Theory is an Explanation of a Law
As stated earlier in this section, a law describes a pattern of data that is observed with no known exception. A theory is a possible explanation for a law. In science, theories can either be descriptive (qualitative) or mathematical (quantitative), but because they explain the patterns described in the law, theory can be used to predict future events. On a popular television show, mathematical theories are used to analyze and describe behavior in order to predict future events. Hypotheses that have survived many supportive tests are often called theories. Theories have a great deal more supportive testing behind them than do hypotheses.

Let's put it together. The Law of Conservation of Mass that you learned earlier stated that matter cannot be created nor destroyed. For example, in the reaction below, you will see that there are 28 g + 6 g = 34 g of reactants (before the arrow) and 34 g of products (after the arrow).

What distinguishes a law from a theory?

Solution:

A law is an observation of nature; a theory is a possible explanation of the law.

Models Developed to Aid in Understanding
Scientists often use models when they need a way to communicate their understanding of what might be very small (such as an atom or molecule) or very large (such as the universe). A model is another way to express a theory.

If you were asked to determine the contents of a box that cannot be opened, you would do a variety of experiments in order to develop an idea (or a model) of what the box contains. You would probably shake the box, perhaps put magnets near it and/or determine its mass. When you completed your experiments, you would develop an idea of what is inside; that is, you would make a model of what is inside a box that cannot be opened.

A good example of how a model is useful to scientists is the kinetic molecular theory. The theory can be defined in statements, but it becomes much more easily understood if representations of the particles in their three phases are drawn.

Another example is how models were used to explain the development of the atomic theory. As you will learn in a later chapter, the idea of the concept of an atom changed over many years. In order to understand each of the different theories of the atom according to the various scientists, models were drawn, and more easily understood.

Lesson Summary

 * A natural law is an observation, or a description of a large amount of reproducible data.
 * A hypothesis is a early attempt at an explanation for data.
 * A theory is used to explain a law or to explain a series of facts/events.
 * Theories can use qualitative analogies or models to describe results.

Review Questions

 * 1) Jack performed an experiment where he measured the masses of two different reactants and the resulting product. His results are shown in the equation below. What law is Jack demonstrating in his experiment?
 * (a) law of constant composition
 * (b) law of combining volumes
 * (c) law of conservation of mass
 * (d) law of conservation of energy
 * (e) law of multiple proportions
 * 1) Sugar dissolves in water. What kind of a statement is this?
 * (a) a hypothesis
 * (b) a law
 * (c) a theory
 * (d) a rule
 * (e) all of the above
 * 1) Draw a model to represent the difference between a solid, a liquid, and a gas. In your model, use symbols to represent the molecules that are present in each state. The model should then show how the molecules exist in each state.
 * 1) Draw a model to represent the difference between a solid, a liquid, and a gas. In your model, use symbols to represent the molecules that are present in each state. The model should then show how the molecules exist in each state.

Vocabulary

 * hypothesis
 * An educated guess as to what is going to happen in the experiment.


 * model
 * A description, graphic, or 3-D representation of theory used to help enhance understanding.


 * natural law
 * A description of the patterns observed in the large amounts of data.


 * scientific method
 * The method of deriving the theories from hypotheses and laws through experimentation and observation.


 * theory
 * Used to explain a law or to explain a series of facts/events.