{"id":86,"date":"2018-03-19T15:30:42","date_gmt":"2018-03-19T15:30:42","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-orgbiochemistry\/chapter\/measurements\/"},"modified":"2018-07-29T19:32:59","modified_gmt":"2018-07-29T19:32:59","slug":"measurements","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-monroecc-orgbiochemistry\/chapter\/measurements\/","title":{"raw":"1.3 Measurements","rendered":"1.3 Measurements"},"content":{"raw":"
\r\n
<\/div>\r\n<\/div>\r\n
\r\n
\r\n
\r\n
\r\n

Learning Objectives<\/h3>\r\n
    \r\n \t
  1. Express quantities properly, using a number and a unit, with awareness of uncertainly.<\/li>\r\n<\/ol>\r\n<\/div>\r\n \r\n\r\nA coffee maker\u2019s instructions tell you to fill the coffeepot with 4 cups of water and use 3 scoops of coffee. When you follow these instructions, you are measuring. When you visit a doctor\u2019s office, a nurse measures your temperature, height, weight, and perhaps blood pressure<\/span>.\r\n<\/span>\r\n\r\nChemists measure the properties of matter and express these measurements as quantities. A\u00a0quantity<\/span><\/span><\/strong>\u00a0is an amount of something and consists of a\u00a0number<\/span><\/span><\/strong>\u00a0and a\u00a0unit<\/span><\/span><\/strong>. The digits reported in a measurement imply the uncertainty<\/strong> of the measurement, which will be considered further in Section 1.5.\u00a0 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 \u201c5 kilometers,\u201d 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 far he or she walks from home to school, and the friend answers \u201c12\u201d without specifying a unit, you do not know whether your friend walks\u2014for example, 12 miles, 12 kilometers, 12 furlongs, or 12 yards.\u00a0Both a number and a unit must be included to express a quantity properly.<\/em><\/span>\r\n\r\n<\/div>\r\n

    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.<\/p>\r\n\r\n

    \r\n

    Example 3<\/h3>\r\n

    Identify the number and the unit in each quantity.<\/p>\r\n\r\n

      \r\n \t
    1. one dozen eggs<\/li>\r\n \t
    2. 2.54 centimeters<\/li>\r\n \t
    3. a box of pencils<\/li>\r\n \t
    4. 88 meters per second<\/li>\r\n<\/ol>\r\n

      Solution<\/p>\r\n\r\n

        \r\n \t
      1. The number is one, and the unit is dozen eggs.<\/li>\r\n \t
      2. The number is 2.54, and the unit is centimeter.<\/li>\r\n \t
      3. The number 1 is implied because the quantity is only a<\/em> box. The unit is box of pencils.<\/li>\r\n \t
      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.<\/li>\r\n<\/ol>\r\n<\/div>\r\n
        \r\n
        \r\n

        Skill-Building Exercise<\/h3>\r\n

        Identify the number and the unit in each quantity.<\/p>\r\n\r\n

          \r\n \t
        1. \r\n
          \r\n

          99 bottles of soda<\/p>\r\n\r\n<\/div><\/li>\r\n \t

        2. \r\n
          \r\n

          60 miles per hour<\/p>\r\n\r\n<\/div><\/li>\r\n \t

        3. \r\n
          \r\n

          32 fluid ounces<\/p>\r\n\r\n<\/div><\/li>\r\n \t

        4. \r\n
          \r\n

          98.6 degrees Fahrenheit<\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n

          \r\n
          \r\n
          \r\n

          Concept Review Exercise<\/h3>\r\n
            \r\n \t
          1. \r\n
            \r\n

            What are the two necessary parts of a quantity?<\/p>\r\n

            [reveal-answer q=\"487579\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"487579\"]1.The two necessary parts are the number and the unit.[\/hidden-answer]<\/p>\r\n\r\n<\/div><\/li>\r\n<\/ol>\r\n<\/div>\r\n

            <\/div>\r\n<\/div>\r\n
            \r\n
            \r\n

            To Your Health: Dosages<\/h3>\r\n<\/div>\r\n
            \r\n

            As we saw in the chapter-opening essay, a medicine can be more harmful than helpful if it is not taken in the proper dosage. A dosage (or dose) is the specific amount of a medicine that is known to be therapeutic for an ailment in a patient of a certain size. Dosages of the active ingredient in medications are usually described by units of mass, typically grams or milligrams, and generally are equated with a number of capsules or teaspoonfuls to be swallowed or injected. (For more information about mass, see Section 1.6 \"The International System of Units\"<\/a>.) The amount of the active ingredient in a medicine is carefully controlled so that the proper number of pills or spoonfuls contains the proper dose.<\/p>\r\n

            Most drugs must be taken in just the right amount. If too little is taken, the desired effects will not occur (or will not occur fast enough for comfort); if too much is taken, there may be potential side effects that are worse than the original ailment. Some drugs are available in multiple dosages. For example, tablets of the medication levothyroxine sodium, a synthetic thyroid hormone for those suffering from decreased thyroid gland function, are available in 11 different doses, ranging from 25 micrograms (\u00b5g) to 300 \u00b5g. It is a doctor\u2019s responsibility to prescribe the correct dosage for a patient, and it is a pharmacist\u2019s responsibility to provide the patient with the correct medicine at the dosage prescribed. Thus, proper quantities\u2014which are expressed using numbers and their associated units\u2014are crucial for keeping us healthy.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n

            \r\n
            \r\n

            Key Takeaway<\/h3>\r\n<\/div>\r\n
            \r\n