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2.1: Taking Measurements

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    ⚙️ Learning Objectives

    • Express quantities properly, using a number and a unit.

    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. When you visit a doctor’s office, a nurse checks your temperature, height, weight, and perhaps blood pressure (Figure \(\PageIndex{1}\)); the nurse is also measuring.

    US Navy 050310-N-1159B-114 Lt. Cmdr. Lisa Kromanaker, a nurse assigned to Operational Health Support Unit Great Lakes, Ill., measures the blood pressure of a Nicaraguan woman during a Medical Readiness Training Exercise.
    Figure \(\PageIndex{1}\): Lt. Cmdr. Lisa Kromanaker measures the blood pressure during a Medical Readiness Training Exercise.

    Chemists measure the properties of matter and express these measurements as quantities. A quantity is an amount of something and consists of a number and a unit. The number tells us how many (or how much), and the unit tells us what the scale of measurement is. For example, when a distance is reported as “5 kilometers,” we know that the quantity has been expressed in units of kilometers and that the number of kilometers is 5. If you ask a friend how long is their walk from home to school, and the friend answers “12” without specifying a unit, you do not know whether your friend walks 12 kilometers, 12 miles, 12 minutes, or 12 hours. Both a number and a unit must be included to express a quantity properly.

    To understand chemistry, we need a clear understanding of the units chemists work with and the rules they follow for expressing numbers. The next two sections examine the rules for expressing numbers.

    ✅ Example \(\PageIndex{1}\)

    Identify the number and the unit in each quantity.

    1. one dozen eggs
    2. 2.54 centimeters
    3. a box of pencils
    4. 88 meters per second


    1. The number is one dozen, and the unit is eggs.
    2. The number is 2.54, and the unit is centimeter.
    3. The number 1 is implied because the quantity is only a box. The unit is box of pencils.
    4. The number is 88, and the unit is meters per second. Note that in this case the unit is actually a combination of two units: meters and seconds.


    • Identify a quantity properly with a number and a unit.



    This page is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Marisa Alviar-Agnew, Henry Agnew, and Lance S. Lund (Anoka-Ramsey Community College).

    2.1: Taking Measurements is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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