Observations
Observation is very important when using scientific methods to investigate phenomena. Observation involves using the senses to gather information about the natural world. Science depends on keeping records of observations for later interpretations. These interpretations may lead to the development of theories or laws. Without accurate observations, scientists cannot make any interpretations and therefore cannot draw conclusions.
Quantitative and Qualitative Observations Defined
There are two types of observations: quantitative and qualitative. Quantitative observations involve measurements or estimates of measurements. Quantitative observations yield meaningful numeric results. Qualitative observations yield descriptive, non-numeric results. Although all the observations we can make about a phenomenon are valuable, quantitative observations are often more useful than qualitative ones. Qualitative observations are somewhat vague because they involve comparative terms.
A qualitative observation would be, for example, “The attendance clerk is a small woman.” If the observer is 6 feet 4 inches tall, he might refer to a woman who is 5 feet 8 inches tall as “small.” But if the observer reported this observation to a person who is 5 feet 2 inches tall, the listener would not acquire a good idea of the height of the attendance clerk because he would not think a woman who is 5 feet 8 inches tall is “small.”
The description “a small woman” could refer to any woman whose height was between 3 feet and 6 feet, depending on who did the observing. Similarly, “a small car” could refer to anything from a compact car to a child’s toy car. The word “small” is a comparative term. The same is true for all words like tall, short, fast, slow, hot, cold, and so forth. These words do not have exact meanings. Under various circumstances, temperatures of
F, F, F, and F could all be described as “hot.” The word “hot” does not convey as much information as the numerical description. Even observations of colors are not exact since there are many shades of each color. Two people may both be wearing red shirts, but the colors of the shirts may not be the same. Exact descriptions of colors would require reporting the frequency or wavelength of the color.
Quantitative observations, on the other hand, have numbers and units associated with them and convey more information. Even if the number is only an estimate, it is more valuable than no number at all.
Sample Questions
Pick out the quantitative and qualitative observations from each phrase:
3.0 g (grams) of NaCl dissolve in 10 mL (milliliter) of H2O to produce a clear solution.
The spider on the wall has only seven legs remaining but is still big and hairy.
When 0.50 mL of a solution is put into a flame, the flame turns a brilliant green.
Solutions
Quantitative: 3.0 g and 10 mL; Qualitative: clear solution
Quantitative: seven legs; Qualitative: big and hairy
Quantitative: 0.50 mL; Qualitative: brilliant green
From http://www.ck12.org/book/Introductory-Chemistry/r1/section/1.2/Introduction-to-Chemistry-and-The-Nature-of-Science-%253A%253Aof%253A%253A-Introductory-Chemistry/