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Chemistry Notes - Ch 1 Measurements GOALS Learn and use the...

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3/24/11 Ch. 1: Measurements GOALS Learn and use the base units and prefixes in the metric system for unit conversions Use scientific notation Differentiate between measured number and exact numbers Determine the SF in a measurement and appropriate rounding rules to report answer with correct number of SF (various
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3/24/11 Physical quantities are described by both a number and a unit . Examples: 37.0 centimeters (cm), 2.05 grams (g), 4.2 inches (in), 0.55 liters (L) All measurements are “inexact” numbers (there is a degree of uncertainty associated with it). Are all numbers inexact ? Could 5 + 2 = 1 be possible? NOPE! Numbers that are counted or part of a definition (an equality/conversion factor) are called “EXACT” numbers .
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Stating a Measurement In every measurement, a number is followed by a unit . Observe the following examples of measurements: Number and Unit 35 m 0.25 L 225 lb In reality, you take and use MEASUREMENTS everyday, you just don’t think about it… calculate how late you can sleep/stay in bed/hit snooze, planning wardrobe (T), checking driving speed, weighing, nutritional information, volume of liquid in drinks, cooking… Most of you are planning careers that depend on your ability to take and communicate ACCURATE measurements to other professionals.
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3/24/11 The Metric System and “ SI Units The metric system and SI (international system) are § related decimal systems based on 10 § used in most of the world § used everywhere by scientists – WHY??? These are the “metric system BASE UNITS” – very important!
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BASE UNITS for metric system For mass use GRAM” (g) For length use “ METER” (m) For liquid volume use LITER” (L) These BASE UNITS may be used alone or may contain a prefix so the unit is more appropriate for the object being measured. Volume: 1mL = 1cc = 1 cm3
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Length Measurement BASE UNIT: meter (m) Length § Can be measured using a meter stick or similar metric scale (smaller or larger)
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3/24/11 Different ways of reporting amounts are all around us – understand that these are EQUALITIES (SAME amount, just reported Which is the correct unit? It depends on what is being
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Inches and Centimeters § 1.00 inch is equal to exactly 2.54 centimeters in the metric system 1.00 in. = 2.54 cm “English System” vs. “Metric System” Need EQUALITIES to be used as conversion factors “one equality ALWAYS gives you TWO conversion
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3/24/11
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Volume Measurement BASE UNIT: Liter (L) Volume § is the space occupied by a substance § Can be measured using a graduated cylinder for liquids § 1 L = 1.06 qt or
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3/24/11 Mass Measurement BASE UNIT: gram (g) The mass of an object § is a measure of the quantity of material it contains § is measured on a balance § uses the unit gram (g) in the metric system
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3/24/11 Various systems of measurement exist, some are easier to use than others Regardless of which system you prefer (science prefers METRIC), all measurements require a UNIT after a NUMBER.
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