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Chemistry Chapter 2

Chemistry Chapter 2. Measurements & Calculations. 2.1 Scientific Method Pages 28-31. Systematic method of study Used to verify results of previous work. Observation. info received by senses recorded as data Qualitative – verbal descriptions

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Chemistry Chapter 2

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  1. Chemistry Chapter 2 Measurements & Calculations

  2. 2.1 Scientific MethodPages 28-31 • Systematic method of study • Used to verify results of previous work

  3. Observation • info received by senses recorded as data • Qualitative – verbal descriptions • Quantitative – descriptions that include number (measurements)

  4. Hypothesis • educated guess • (possible solution)

  5. Experiment • a set of controlled observations that test a hypothesis • Devised to test one variable at a time • Independent variable: variable that experimenter has control over • Dependent variable: changes in response to IV, change is measured • Constant: factor that is not allowed to change during the experiment • Control: a standard for comparison

  6. Data Analysis • careful examination and review of all data for meaning

  7. Conclusion • judgment based on observations • Hypothesis is true: • experiment is repeated • Hypothesis is not true: • experiment is revised or rejected

  8. Model • representation used to help deal with abstract ideas and objects • Visual, mathematical, verbal

  9. Theory • a broad explanation of some relationship supported by observations • Atomic theory • Kinetic molecular theory

  10. Law • a rule of nature • (states relationship, does not explain) • Newton’s laws of motion • Law of conservation of matter • Law of conservation of energy • (early 1900’s, Einstein discovered that E=mc2. New law of conservation of mass-energy was proposed)

  11. CH. 2.2 MEASUREMENT II. Units of Measurement (pages 33 - 39)

  12. A. Number vs. Quantity • Quantity - number + unit UNITS MATTER!!

  13. B. SI Units Quantity Symbol Base Unit Abbrev. Length l meter m Mass m kilogram kg Time t second s Temp T Kelvin K Amount n mole mol

  14. kilo- mega- giga- M G k 103 109 106 deci- BASE UNIT d --- 10-1 100 centi- c 10-2 milli- m 10-3 micro-  10-6 nano- n 10-9 pico- p 10-12 B. SI Units Prefix Symbol Factor

  15. M V D = C. Derived Units • Combination of base units. • Volume (m3 or cm3) • length  length  length 1 cm3 = 1 mL 1 dm3 = 1 L • Density (kg/m3 or g/cm3) • mass per volume

  16. D. Density Mass (g) Volume (cm3)

  17. D. Density • An object has a volume of 825 cm3 and a density of 13.6 g/cm3. Find its mass. GIVEN: V = 825 cm3 D = 13.6 g/cm3 M = ? WORK: M = DV M = (13.6 g/cm3)(825cm3) M = 11,200 g

  18. WORK: V = M D V = 25 g 0.87 g/mL D. Density • A liquid has a density of 0.87 g/mL. What volume is occupied by 25 g of the liquid? GIVEN: D = 0.87 g/mL V = ? M = 25 g V = 29 mL

  19. CH. 2 - MEASUREMENT III. Unit Conversions (p. 40 - 42)

  20. To the left or right? A. SI Prefix Conversions 1. Find the difference between the exponents of the two prefixes. 2. Move the decimal that many places.

  21. NUMBER = UNIT A. SI Prefix Conversions 0.532 532 m = _______ km NUMBER UNIT

  22. kilo- mega- M k 106 103 deci- BASE UNIT d --- 100 10-1 centi- c 10-2 milli- m 10-3 micro-  10-6 nano- n 10-9 pico- p 10-12 A. SI Prefix Conversions Prefix Symbol Factor move left move right

  23. 1) 20 cm = ______________ m 2) 0.032 L = ______________ mL 3) 45 m = ______________ nm 4) 805 dm = ______________ km A. SI Prefix Conversions 0.2 32 45,000 0.0805

  24. B. Dimensional Analysis • The “Factor-Label” Method • Units, or “labels” are canceled, or “factored” out

  25. B. Dimensional Analysis • Steps: 1. Identify starting & ending units. 2. Line up conversion factors so units cancel. 3. Multiply all top numbers & divide by each bottom number. 4. Check units & answer.

  26. B. Dimensional Analysis • Lining up conversion factors: = 1 1 in = 2.54 cm 2.54 cm 2.54 cm 1 = 1 in = 2.54 cm 1 in 1 in

  27. qt mL  B. Dimensional Analysis • How many milliliters are in 1.00 quart of milk? 1 L 1.057 qt 1000 mL 1 L 1.00 qt = 946 mL

  28. lb cm3 B. Dimensional Analysis • You have 1.5 pounds of gold. Find its volume in cm3 if the density of gold is 19.3 g/cm3. 1 cm3 19.3 g 1 kg 2.2 lb 1000 g 1 kg 1.5 lb = 35 cm3

  29. in3 L B. Dimensional Analysis • How many liters of water would fill a container that measures 75.0 in3? 1 L 1000 cm3 (2.54 cm)3 (1 in)3 75.0 in3 = .191 L

  30. cm in B. Dimensional Analysis 5) Your European hairdresser wants to cut your hair 8.0 cm shorter. How many inches will he be cutting off? 8.0 cm 1 in 2.54 cm = 3.2 in

  31. cm yd B. Dimensional Analysis 6) Taft football needs 550 cm for a 1st down. How many yards is this? 1 yd 3 ft 1 ft 12 in 1 in 2.54 cm 550 cm = 6.0 yd

  32. cm pieces B. Dimensional Analysis 7) A piece of wire is 1.3 m long. How many 1.5-cm pieces can be cut from this wire? 1 piece 1.5 cm 100 cm 1 m 1.3 m = 86 pieces

  33. CH. 2 - MEASUREMENT I. Using Measurements (p. 44 - 57)

  34. A. Accuracy vs. Precision • Accuracy - how close a measurement is to the accepted value • Precision - how close a series of measurements are to each other ACCURATE = CORRECT PRECISE = CONSISTENT

  35. your value accepted value B. Percent Error • Indicates accuracy of a measurement

  36. % error = 2.9 % B. Percent Error • A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL.

  37. C. Significant Figures • Indicate precision of a measurement. • Recording Sig Figs • Sig figs in a measurement include the known digits plus a final estimated digit 2.35 cm

  38. C. Significant Figures • Counting Sig Figs (Table 2-5, p.47) • Count all numbers EXCEPT: • Leading zeros -- 0.0025 • Trailing zeros without a decimal point -- 2,500

  39. C. Significant Figures Counting Sig Fig Examples 1. 23.50 1. 23.50 4 sig figs 3 sig figs 2. 402 2. 402 3. 5,280 3. 5,280 3 sig figs 2 sig figs 4. 0.080 4. 0.080

  40. 3 SF C. Significant Figures • Calculating with Sig Figs • Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. (13.91g/cm3)(23.3cm3) = 324.103g 4 SF 3 SF 324g

  41. C. Significant Figures • Calculating with Sig Figs (con’t) • Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer. 224 g + 130 g 354 g 224 g + 130 g 354 g 3.75 mL + 4.1 mL 7.85 mL 3.75 mL + 4.1 mL 7.85 mL  350 g  7.9 mL

  42. C. Significant Figures • Calculating with Sig Figs (con’t) • Exact Numbers do not limit the # of sig figs in the answer. • Counting numbers: 12 students • Exact conversions: 1 m = 100 cm • “1” in any conversion: 1 in = 2.54 cm

  43. 5. (15.30 g) ÷ (6.4 mL)  2.4 g/mL 2 SF C. Significant Figures Practice Problems 4 SF 2 SF = 2.390625 g/mL 6. 18.9 g - 0.84 g  18.1 g 18.06 g

  44. D. Scientific Notation • Converting into Sci. Notation: • Move decimal until there’s 1 digit to its left. Places moved = exponent. • Large # (>1)  positive exponentSmall # (<1)  negative exponent • Only include sig figs. 65,000 kg  6.5 × 104 kg

  45. 7. 2,400,000 g 8. 0.00256 kg 9. 7  10-5 km 10. 6.2  104 mm D. Scientific Notation Practice Problems 2.4  106 g 2.56  10-3 kg 0.00007 km 62,000 mm

  46. EXE EXP EXP ENTER EE EE D. Scientific Notation • Calculating with Sci. Notation (5.44 × 107 g) ÷ (8.1 × 104 mol) = Type on your calculator: 5.44 7 8.1 4 ÷ = 671.6049383 = 670 g/mol = 6.7 × 102 g/mol

  47. Problem-Solving Steps 1. Analyze 2. Plan 3. Compute 4. Evaluate

  48. y y x x E. Proportions • Direct Proportion • Inverse Proportion

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