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Chapters 1 & 2: Measurement and Calculations

Chapters 1 & 2: Measurement and Calculations. Learning Targets Identify a given substance as an element or compound Classify properties and changes as chemical or physical Explain the structure of the periodic including properties of elements based on their location (metal, nonmetal, etc.)

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Chapters 1 & 2: Measurement and Calculations

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  1. Chapters 1 & 2:Measurement and Calculations Learning Targets Identify a given substance as an element or compound Classify properties and changes as chemical or physical Explain the structure of the periodic including properties of elements based on their location (metal, nonmetal, etc.) Determine the amount of heat transferred in a process Express data and results of calculations with appropriate significant figures, units, and in scientific notation Calculate percent error from lab data and use this to evaluate the quality of lab data Perform density calculations and apply density conceptually (e.g. identifying substances or determining if an object will float

  2. Key Words • atom • compound • element • pure substance • mixture • homogeneous/heterogeneous • chemical change/property • physical change/property • direct/inverse proportion • family/group • period • significant figure • scientific notation • conversion factor • percent error • metal • nonmetal • metalloid • noble gas • quantitative • qualitative

  3. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 A key skill in chemistry is being able to convert from one unit of measurement to another For example, converting from one unit of distance to another such as feet to miles Using conversion factors is done using the same approach taken to multiplying fractions

  4. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 Determine the answers to following problems:

  5. Sample: What does 3 x 2/3 equal? • 2 • 3 • 1/2 • 3/2 • 6 0 of 0

  6. Sample: What is the product of 3/4 and 2/3? • 3 • 4 • 2/3 • 3 • 1/2 0 of 2

  7. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 In each case, notice how a common numerator and denominator cancelled each other This same idea is the key idea to using conversion factors With conversion factors, the difference is that you select the fraction to the answer you want

  8. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 To convert one unit to another, e.g. pounds to grams, the same principles as above are used Arrange units as needed to get the desired unit The fraction used to convert one unit to another is known as a conversion factor pounds x ---------------- = grams

  9. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 Set up the appropriate conversion factor for the following: Inches to centimeters Miles per hour to meters per minute

  10. Sample: What is the correct conversion factor for converting feet to inches?

  11. Sample: What is the correct conversion factor to convert feet per second to inches per minute?

  12. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 The numerical relationship between units must be taken into account as well For example, to convert feet to inches, you need to know that there are 12 inches in one foot Once the units are in place, the final step is to put each number with its unit Potentially Useful Information 1 ft3 = 28.32 L 1 mi = 1.609 km 1 in3 = 16.38 cm3 1 in = 2.54 cm 1 kg = 2.2 lbs 1 oz = 28.35 g 1 lb = 16 oz 1 gallon = 3.785 L 1 lb = 453.59 g 1 ft = 12 in 1 ft3 = 1728 in3 3 ft = 1 yd 1 m = 3.281 ft 1 mi = 5280 ft 1 cal = 4.184 J

  13. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 Determine the answers to following problems: a) How many inches are there in 2.0 feet? b) What is 12 miles per hour in meters per minute?

  14. Sample: How many grams are equal to a mass of 10.0 pounds? • .022 g • 4535.9 g • 45.359 g • 22 g

  15. Sample: What speed, in meters per minutes, is equivalent to 20.0 feet per second? • 3930 m/min • .101 m/min • 1.09 m/min • 366 m/min

  16. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 Pay special attention to any unit containing the word “per”; for example:miles per hour – mi/hr meters per second – m/s grams per mole – g/mol grams per liter – g/L These units are always determined by dividing the two units grams per mole = grams ÷ moles

  17. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 When a measurement has a unit with the word “per” in it, it is a conversion factor For example, speed in mi/hr is the number of miles driven in 1 hour 25 miles per hour means 25 miles in I hour, so….25 miles = 1 hour

  18. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 Determine the answers to following problem: a) If your drive for four hours at a speed of 25 miles per hour, how many miles will you drive?

  19. Sample: A metal has a density of 17.4 g/mL. How many mL of space will 11. 1 g of this metal occupy? • 17.4 mL • 11.1 mL • .638 mL • 1.57 mL

  20. Sample: The molar mass of a substance is measured in the unit of grams per mole. If a sample of a substance is found to contain 3.55 moles and a mass of 79.2 grams, what is its molar mass? • .0448 g/mol • 22.3 g/mol • 3.55 g/mol • 281 g/mol

  21. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 Metric conversions (mL to L, g to kg) can be performed without the use of conversion factors To convert these unit, just move the decimal the appropriate number of places This works because the metric prefixes always change the value of a number by a factor of 10, which is what you do when you move a decimal point

  22. Section 1: Conversion FactorsPages 40-42 RBQs Pgs. 60-61 #28-32, 49 Kangaroos Have Dandruff But Don’t Care Much

  23. Sample: How many meters are there in 50 cm? • 50 m • 5000 m • 500 m • .05 m • 0.5 m

  24. Sample: How many kilometers are there in 8,230 mm? • 82,300 km • .00823 km • .0823 km • .823 km • 82.3 km

  25. Sample: How many mg are in 46 g? • 46000 g • 4600 g • 460 g • 4.6 g • .046 g

  26. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 Scientific notation is a ay of taking very large numbers and/or very small numbers and writing them more simply For example, an important number in chemistry is 602,000,000,000,000,000,000,000which suck to write…but in scientific notation it is6.02 x 1023

  27. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 • Measurements made in the lab are never perfect • Data can only include numbers that we are sureof • Record all numbers you aresure of, then estimate anadditional number

  28. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 • Numbers given this way are called significant figures • Sig figs also indicate how accurate a measuring device is

  29. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 • Since numbers are often given in a question and not gathered in a lab, it is important to be able to look at a number and determine how many significant figures it contains • Also, the number of significant figures in an answer will depend on the sig figs contained in the numbers in the question • Applying sig fig rules to math ensures that no uncertain numbers will be in your answers

  30. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 Exercise: Use the examples below to come up with a set of rules for converting from scientific to regular notation.

  31. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 Exercise: Use the examples below to come up with a set of rules for converting from regular to scientific notation.

  32. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 When are nonzero numbers significant? (circle one) Always Sometimes Never When are leading zeros significant? (circle one) Always Sometimes Never When are captive zeros significant? (circle one) Always Sometimes Never When are trailing zeros significant? (circle one) Always Sometimes Never If you indicated “sometimes” for any of the above, explain when that zero will be significant below:

  33. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 • Significant figure rules also exist and must be applied when performing calculations • There is one rule for addition and subtraction and a second rule for multiplication and division • The exercises on the following slides will illustrate these rules

  34. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 2.0 x 4 = 89.166 x 3.2 = 292.66543 x 0.0032 = .00850.02 ÷ 0.00606894 = 3 2.44 x 8.629 = 21.1199.2 ÷ 4.05 = 49.20.026 x 0.00449 = .00012(5.4 x 102)(6.39 x 10-6) = 3.5 x 10-3 Determine the number of significant figures in each answer above. Determine the number of significant figures in each number in the questions above. How is the number of significant figures in the answer determined? (write in space below)

  35. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 X & ÷ 2.0 x 4 = 89.166 x 3.2 = 292.66543 x 0.0032 = .00850.02 ÷ 0.00606894 = 3 2.44 x 8.629 = 21.1199.2 ÷ 4.05 = 49.20.026 x 0.00449 = .00012(5.4 x 102)(6.39 x 10-6) = 3.5 x 10-3 Determine the number of significant figures in each answer above. Determine the number of significant figures in each number in the questions above. How is the number of significant figures in the answer determined? (write in space below)

  36. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 + & - 8.663 – 2.1 = 6.61.00036 + 0.2 = 1.28.365434534385 + 1 = 968.633 + 7.9343 = 76.567 14.2 + 2 = 169.887467 – 2.003 = 7.8846.22 + 2.1 = 8.34.0 + 12.98373 = 17.0 Determine the number of decimal places in each answer above. Determine the number of decimal places in each number in the questions above. How is the number of decimal places in the answer determined? (write in space below)

  37. Sample: What is the product of 4.56 and 1.4, reported with correct significant figures? • 6.384 • 6.38 • 6.3 • 6.4 • 6

  38. Sample: What is 4.56 - 1.4, reported with correct significant figures? • 3.16 • 3.2 • 3.1 • 3.160 • 3

  39. Sample: Do this! And with correct sig figs! 4.184 x 100.62 x (25.27 – 24.16) = ?

  40. Sample: Do this! And with correct sig figs! (6.0 x 1023)(4.22) = ?

  41. Section 2: Scientific Notation & Sig FigsPages 46-52 RBQs Pgs. 59-61 #21-23, 36-46 • When using conversion factors, the conversion factor has nothing to do with the number of significant figures. Sample: What is the volume in mL of a substance that has a mass of 5.00 grams and a density of 2.1 g/mL?

  42. Section 3: Units, Density, and % ErrorPages 59-61 RBQs Pgs. 59-61 #14, 26-29, 30-35, 48, 50 • Data can be either quantitative or qualitativeQuantitative:Qualitative:Quantitative data is data obtained through measurements

  43. Section 3: Units, Density, and % ErrorPages 59-61 RBQs Pgs. 59-61 #14, 26-29, 30-35, 48, 50 • Every measurement needs a number and a unit • In chemistry, SIunitsare used to report measurement

  44. Section 3: Units, Density, and % ErrorPages 59-61 RBQs Pgs. 59-61 #14, 26-29, 30-35, 48, 50 • The base units can be modified using metric prefixes

  45. Section 3: Units, Density, and % ErrorPages 59-61 RBQs Pgs. 59-61 #14, 26-29, 30-35, 48, 50 • Derived units can be made from the base units • These units include volume and density 1. What formula is used to find the volume of a cube?2. What units are used to measure a cube’s dimensions?3. Therefore, what are possible volume units?

  46. Section 3: Units, Density, and % ErrorPages 59-61 RBQs Pgs. 59-61 #14, 26-29, 30-35, 48, 50 • Density is the ratio of an object’s mass to its volume • Mass measures the amount of matter present • Volume measures the space occupied by matter • And since a ratio is just a fraction •What are some possible units for density?

  47. Sample: A sample of liquid with a volume of 23.50 mL has a mass of 35.062 g. What is the density of this liquid?

  48. Sample: What is the volume of a sample of liquid mercury that has a mass of 76.2 g, given that the density of mercury is 13.6 g/mL?

  49. Section 3: Units, Density, and % ErrorPages 59-61 RBQs Pgs. 59-61 #14, 26-29, 30-35, 48, 50 • Density can be usedto identify unknownsubstances • It can also be used todetermine if an objectwill float

  50. Section 3: Units, Density, and % ErrorPages 59-61 RBQs Pgs. 59-61 #14, 26-29, 30-35, 48, 50 • Percent error is a measure of the accuracy of lab results. It indicates how far data is from the true value

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