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Zumdahl Zumdahl DeCoste CHEMISTRY World of

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Chapter 5 Measurements and Calculations

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Goals of Chapter 5: Measurement & Calculations Express numbers in scientific notation Learn English, metric, & SI system of measurement Use metric system to measure length, volume, and mass Significant digits Dimensional Analysis Temperature Scales Density/Specific Gravity Copyright © Houghton Mifflin Company5-3

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Qualitative vs. Quantitative Qualitative: appearance. – the substance was a white powder Quantitative: Measurement – The substance had a mass of 5.6 grams Copyright © Houghton Mifflin Company5-4

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Why are measurements important? Pay for gasoline by the gallon Construction: must have accurate measurements Welding: measurements must be accurate Automobiles: Most items on cars have a measurement Landscaping: Measurements important for spatial relationships Copyright © Houghton Mifflin Company5-5

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Measurements: 2 Parts Number + Unit – Number alone is meaningless If I tell you a 2 x 4 is 5 long – what does this mean: 5 feet, 5 inches, 5 meters? – Unit alone is meaningless If I tell you the 2 x 4 is feet long – what does this mean: 2 ft, 4 ft, 8 ft? ALWAYS INCLUDE BOTH NUMBER AND UNIT! Copyright © Houghton Mifflin Company5-6

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Scientific Notation Used to express very large or very small numbers Express using number between 1 & 10 multiplied by a power of 10 – 10 is to positive power for large numbers – 10 is to a negative number for small numbers (decimals) Copyright © Houghton Mifflin Company5-7

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Large Numbers Copyright © Houghton Mifflin Company5-8 Decimal point moved to left Power of 10 = # places moved = + number 125 = 1.25 x 100 = 1.25 x 10 2 Decimal point moved 2 places left 1700 = 1.7 x 1000 = 1.7 x 10 3 Decimal point moved 3 places left 93,000,000 = 9.3 x 10 7 Decimal point moved 7 places left

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Small Numbers (Decimals < 1.0) Copyright © Houghton Mifflin Company5-9 Decimal point moved to the right Power of 10 = # places moved = negative number 0.010 = 1.0 x 0.010 = 1.0 x 10 -2 Decimal point moved right 2 places 0.000167 = 1.67 x 10 -4 Decimal point moved right 4 places 0.089 = 8.9 x 10 -2 Decimal point moved right 2 places

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Units Tell us what scale or standard is being used to represent measurement Scientists need common units to represent quantities like mass, length, time, and temperature If everyone had own set of units – chaos would result US uses English system, most of world (& scientists) use metric system, also SI system Copyright © Houghton Mifflin Company5-10

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BASIC UNITS Physical QuantityEnglish SystemMetric System Mass Pound or slug Gram or kilogram Length inch, foot, yard Centimeter or meter Volume Quart or gallon Liter, milliliter, or cm 3 Time Hours, minutes, seconds Seconds Temperature Degrees Fahrenheit °C or Kelvin Copyright © Houghton Mifflin Company 5-11

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Metric Prefixes Copyright © Houghton Mifflin Company5-12 Kilo- hecto- deka- UNIT deci- centi- milli- k h dk d c m Move decimal point left Move decimal point right Power of 10 between each increment

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Examples Copyright © Houghton Mifflin Company5-13 1000 meters = 1 km (decimal moved 3 places left) 1 meter = 100 cm (decimal moved 2 places right) 10 mm = 1 cm (decimal moved 1 place left) 1 Liter = 1000 mL (decimal moved 3 places to right) 600 grams = 0.6 kg (decimal moved 3 places left)

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Table 5.2 Copyright © Houghton Mifflin Company5-14

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Table 5.3 Copyright © Houghton Mifflin Company5-15

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Figure 5.1: Comparison of English and metric units. Copyright © Houghton Mifflin Company5-16

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Figure 5.2: Cube representations. Copyright © Houghton Mifflin Company5-17

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Figure 5.3: A 100 mL graduated cylinder. Copyright © Houghton Mifflin Company5-18 1 mL = 1 cm 3 1 milliliter = 1 cubic centimeter 100 mL = 100 cm 3

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Dimensional Analysis Copyright © Houghton Mifflin Company5-19

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Uncertainty of Measurement When using instrument to measure (such as a ruler or graduated cylinder), we visualize divisions between markings and estimate When making measurement, record all certain numbers and first uncertain number Copyright © Houghton Mifflin Company5-20

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Figure 5.5: Measuring a pin. Copyright © Houghton Mifflin Company5-21 These divisions were visualized Reading is between 2.8 cm & 2.9 cm 2.85 cm is measurement “5” is uncertain

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Significant Figures Ex. Includes all numbers recorded in a measurement – For pin, length = 2.85 cm: 3 significant figures – All certain numbers plus first uncertain Assume to be accurate to ± 1 in last # – Pin length is 2.85 ± 0.01 cm – Pin is somewhere between 2.84 & 2.86 cm Copyright © Houghton Mifflin Company5-22

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Rules for Counting Significant Figures Significant – Captive zeros (between nonzero digits) Example: 1.008 (4 s.f. - all numbers are significant) – Trailing zeros (right end of number) Significant if bar is placed over zero or over zero to right Example: 200 (only #2 is significant = 1 s.f.) 2Ō0 (2 s.f. - 2 & Ō both significant) 20Ō (3 s.f. - 2 and both zeros are significant)

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– Following decimal to right of nonzero digit = significant 5.00 = 3 s.f. Copyright © Houghton Mifflin Company5-24

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Non-significant zeros – Leading zeros, precede non-zero digits Example: 0.0025 = 2 s.f. - zeros are non- significant Both: some numbers are sig. some are not Copyright © Houghton Mifflin Company5-25

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Rules for counting significant figures (continued) All nonzero integers are significant – Example: 1457 has 4 s.f. Exact numbers have unlimited number of s.f. – Determined by counting 8 apples, 21 students Not obtained from measuring devices From definitions 1 inch is exactly 2.54 cm Will not limit numbers in calculations

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Use same rules for scientific notation (10 x not s.f.) Copyright © Houghton Mifflin Company5-27

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To give answer with correct number of significant figures – round off Look at number to right of last s.f. – If number is <5 round down – If number is ≥5 round up Do not round off until end of calculations

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Rules for s.f. in calculations Multiplication & Division – Answer should have same number of s.f. as measurement with smallest number of s.f. – Example: 4.56 x 1.4 = 6.384 → 6.4 (3 s.f.)(2 s.f.)* (2 s.f.)*

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Addition & Subtraction – Limited by smallest number of decimal places – Example: 12.11 (2 decimal places) 18.0 (1 decimal place)* + 1.013 (3 decimal places) 31.123 → 31.1 (1 decimal place)* Copyright © Houghton Mifflin Company5-30

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Figure 5.6: The three major temperature scales. Copyright © Houghton Mifflin Company5-31

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Temperature Scales Copyright © Houghton Mifflin Company5-32

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Converting between Kelvin & Celsius To convert from Kelvin to Celsius: T °C = T K – 273 Liquid Nitrogen boils at 77K, what is this in Celsius? T °C = 77 – 273 = -196 °C To convert from Celsius to Kelvin: T K = T °C + 273 The bp of water on top of Mt. Everest is 70 °C. Convert to K. T K = 70 + 273 = 343 K

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Figure 5.7: Converting 70 degrees Celsius to Kelvin units. Copyright © Houghton Mifflin Company5-34

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Fahrenheit/Celsius Conversions Copyright © Houghton Mifflin Company5-35 To convert from Celsius to Fahrenheit: T °F = 1.80(T °C ) + 32 If the temperature is 28°C, what is this in °F? T °F = 1.80(28) + 32 = 50.4 + 32 = 82°F (2 s.f.) To convert from Fahrenheit to Celsius: T °C = (T °F – 32)/1.80 If you have a temperature of 101°F, what is this in °C? T °C = (101 – 32)/1.80 = 69/1.8 = 38 °C

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Figure 5.8: Comparison of the Celsius and Fahrenheit scales. Copyright © Houghton Mifflin Company5-36

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Density: amount of matter in a given volume of substance Density = mass / volume Determine mass using a balance Determine volume by calculations, graduated cylinder, or water displacement Units are in g/cm 3, g/mL, kg/L, lb/gal

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Determining volume by water displacement Place water in graduated cylinder & record level Add object Record volume after addition of object Volume is difference between second volume and first volume Copyright © Houghton Mifflin Company5-38

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Figure 5.9: Tank of water. Copyright © Houghton Mifflin Company5-39

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Figure 5.9: Person submerged in the tank. Copyright © Houghton Mifflin Company5-40

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