Scientific Method

Chemistry is a science. Chemists use the scientific method when they investigate matter. There is no one definition of scientific method that is applicable to all sciences; however, the following outline describes an approach that is commonly used by chemists.

1. Observation-a fact or event that we can detect using our senses.
2. Law-a summary of many similar observations, noting their common features or trends.
3. Hypothesis-a possible explanation for the common feature or trend.
4. Experiment-laboratory manipulation to test whether a hypothesis is correct.
5. Theory-a hypothesis that has withstood repeated tests and that is likely to be correct.

Note that these activities are often repeated in a cycle. An experiment provides us new observations, which may lead us to revise laws and hypotheses, which may suggest new experiments.

Here is an example of how the scientific method works.

1. Observation #1-"carbon oxide" consists of the elements carbon and oxygen in a 3 : 4 mass ratio.
2. Observation #2-another "carbon oxide" contains carbon and oxygen in a 3 : 8 mass ratio.
3. Law-if two compounds contain the same elements but in different proportions, the ratio of those proportions will be the same as the ratio of two small whole numbers. (Note: this is called the law of multiple proportions; it was formulated by John Dalton in the early 1800's). In our example above, dividing (3/4) by (3/8) yields (2/1); in other words, compound 2 contains exactly twice as much oxygen as compound 1.
4. Hypothesis #1-each element consists of small, indivisible particles called atoms.
5. Hypothesis #2-each molecule of compound 2 contains two oxygen atoms (CO₂), while compound 1 contains only one oxygen atom (CO).
6. Hypothesis #3-an oxygen atom is 4/3 as massive as a carbon atom.
7. Experiments-thousands of compounds were analyzed by hundreds of chemists throughout Europe. All of the elemental compositions were consistent with the law of multiple proportions.
8. Theory-by the second half of the nineteenth century, most scientists accepted Dalton's atomic theory as being correct.