2.1: Prelude to Measurements

Making good observations is important to the successful application of the scientific method.  Observations are generally qualitative or quantitative.  Qualitative observations rely on descriptions (“the watermelon is heavy”) and quantitative observations involve numerical representation (“the watermelon weighs 50 pounds”) .

A coffee maker’s instructions tell you to fill the coffee pot with 4 cups of water and to use 3 scoops of coffee. When you follow these instructions, you are measuring. Each of these measurements includes three things: a numerical amount (e.g., 4), a unit (cups), and a substance (water). When you visit a doctor’s office and a nurse checks your temperature, height, weight, and blood pressure (Figure 2.1.1), the nurse is also measuring. 

To measure something is to make a quantitative observation. Measuring is comparing an amount of a certain attribute of a body or phenomenon with another amount of the same attribute that we take as a reference. To understand chemistry, we need a clear understanding of the units chemists work with and the rules they follow for expressing numbers and measurements. The next sections examine the rules for these things.