qualitative analysis – what substances are present in a sample, does not involve numbers
quantitative analysis – how much of a given substance is present in a sample, involves numbers
Quantitative observations or measurements are made with instruments that extend the human senses of sight, smell, taste, touch, and hearing. These instruments may be as simple as a ruler or as complicated as a mass spectrometer. They are less likely to be fooled however, than the human senses alone.
Another advantage of measurements is that they are usually reproducible. One of the characteristics of a science is that observations can be repeated both by the original scientist and by other scientists. The results of measurements can be stored in a laboratory notebook or a computer and can be compared easily with similar observations. For example, if one person records the fact that the pages of this book measure ten inches from top to bottom, the observation can easily be proved right or wrong.
Qualitative observations are difficult to check. A sample may look blue to one person and green to another. Even a single person may have difficulty remembering the exact shade of blue or green.
The advantages of quantitative observations are:
1. Instruments are less likely to be fooled than humans
2. Observations made with instruments are usually reproducible
3. Quantitative observations can easily be stored and compared