2. 1 Scientific Measurement

3. 2 What is Chemistry? l Matter - anything that has mass and takes up space. l Chemistry - the study of the composition of matter and the changes that matter undergoes. –Involves all aspects of life b/c all living and nonliving things are made of matter

4. 3 Five Areas of Chemistry l Organic – carbon chemistry l Inorganic – non-carbon chemistry; generally non-living things (ex. Rocks) l Biochemistry – processes in organisms (ex. Muscle contraction and digestion) l Analytical – composition of matter (ex. Measuring amount of Pb (lead) in H 2 O) l Physical – mechanisms, rate, and E transfer

5. 4 Scientific Notation l Chemistry often deals with very large and very small numbers. l There are approximately 602,200,000,000,000,000,000,000 molecules of water in 18 mL l one electron has a mass of 0.000000000000000000000000000911 g l We need a shorter way of writing these numbers

6. 5 Scientific Notation l Consists of two parts 1. a number between 1 and 10 2. multiplied by 10 raised to a power l 602,200,000,000,000,000,000,000 = 6.022 x 10 23 l 0.000000000000000000000000000911 g = 9.11 x 10 -28

7. 6 Putting a number into scientific notation l STEP 1 - Determine how many times you have to move the decimal place to make a number between 1 and 10 l 3240000 = 3.24

8. 7 STEP 2 - Determining the exponent l The number of places you move the decimal becomes the exponent l Starting with a number greater than 1 = a positive exponent l Starting with a number less than 1 = a negative exponent l 0.00045 u 4.5 x 10 -4

9. 8 Going from scientific notation to a “regular” number l Move the decimal place as indicated by the exponent l Negative exponents give you numbers less than one. Positive exponents give you numbers greater than one

10. 9 Examples l 3.21 x 10 4 –32100 l 6.17 x 10 -5 –0.0000617

11. 10 USING YOUR CALCULATOR l EXP button l Adding, subtracting, multiplying, & dividing – USE PARENTHESES

12. 11 PRACTICE

13. 12 How good are the measurements? l Accuracy- how close the measurement is to the actual value l Precision- how well can the measurement be repeated

14. 13 Differences l Accuracy can be true of an individual measurement or the average of several. l Precision requires several measurements before anything can be said about it.

15. 14 Let’s use a golf anaolgy

16. 15 Accurate?No Precise?Yes

17. 16 Accurate?Yes Precise?Yes

18. 17 Precise?No Accurate?Maybe?

19. 18 Accurate?Yes Precise?We can't say!

20. 19 In terms of measurement l Three students measure the room to be 10.1 m, 10.2 m and 10.1 m across. The room is actually 10.5m across. l Were they precise? l Were they accurate?

21. 20 Error l Accepted value (or actual value) –The right answer –Based on reliable references l Experimental Value- what YOU get l Error = experimental value – accepted value l Can be negative

22. 21 Percent Error l Absolute value of error l A man weighs 215 kg using a proven accurate balance. If he uses another, that is not as accurate, and it says 210 kg, what is the percent error?

23. 22 Percent Error Example l Example: I measured a sample of boiling water to be 99.1°C. The text says that water’s boiling point is 100°C. Is there an error? If so, what is the percent error? –Experimental value = 99.1°C –Accepted value = 100°C –Error = 99.1°C– 100°C = -0.9°C –Percent Error = 0.9°C/100°C x 100% = 0.9%

24. 23 Significant Figures l In a measurement, all known digits plus one estimated digit are called significant figures or significant digits l AKA “sig figs” l Tells us about the accuracy of a measurement

25. 24 Significant figures (sig figs) l When we measure something, we can (and do) always estimate between the smallest marks. 21345

26. 25 Significant figures (sig figs) l The better the marks, the better we can estimate. l Scientists always understand that the last number measured is actually an estimate. 21345

27. 26 Significant figures (sig figs) l The measurements we write down tells us about the instrument we use l The last digit is between the lines l What is the smallest mark on the ruler that measures 142.13 cm? 141 142

28. 27 Significant figures (sig figs) l What is the smallest mark on the ruler that measures 142 cm? 10020015025050

29. 28 l 140 cm? l There’s a problem – which ruler was used to measure 140 cm? 10020015025050 100200

30. 29 l 140 cm? l Scientists needed a set of rules to help us know which zeroes are measured and which are estimates 10020015025050 100200

31. 30 RULES of SIG FIGS 1. Non zeros are ALWAYS significant. –46.3 = 3 sig figs 129 = 3 sig figs 2. Zeroes between non zeroes ARE significant l 40.7 = 3 sig figs 2001 = 4 sig figs

32. 31 RULES of SIG FIGS 3. If there’s a decimal, start counting at the first NON-ZERO and count all the way to the end l 0.045 = 2 sig figs l 0.0450 = 3 sig figs l 1.200 = 4 sig figs l 4.00 = 3 sig figs

33. 32 RULES of SIG FIGS 4. If there’s NOT a decimal, ignore any zeroes at the end 270 = 2 sig figs 27 000 = 2 sig figs 2700000000000000 = 2 sig figs

34. 33 l 140 cm? 10020015025050 100200

35. 34 Back to our ruler problem l 140 has 2 significant figures l That tells us the measurement was only taken to the hundreds and the tens are estimated

36. 35 100200 l 140 cm

37. 36 Numbers without sig figs l Counted numbers –12 eggs in a dozen –32 students in a class l Definitions –1 m = 100 cm –16 ounces is 1 pound l AKA “Unlimited” significant figures

38. 37 Scientific notation l Only use first part! l How many sig figs in 1.20 x 10 3 m?

39. 38 Sig figs. l How many sig figs in the following measurements? l 458 g l 4085 g l 4850 g l 0.0485 g l 0.004085 g l 405.0 g l 4050 g l 0.450 g l 4050.05 g l 0.0500060 g

40. 39 Significant Figures l Rules for adding and subtracting –The answer should be rounded to the same number of decimal places as the measurement with the least number of decimal places.

41. 40 For example 27.936.4+ 27.93 6.4+ 34.33 27.93 6.4

42. 41 Multiplication and Division l Rules for multiplying and dividing l The answer should be rounded to the same number of sig figs as the measurement with the least number of sig figs.

43. Volume 50 40 30 20 10 0 How much space an object occupies Graduated Cylinders Come in variety of sizes Measure in milliliters (mL)

44. l Meniscus - the curve the water takes in the cylinder How to Measure Volume 50 40 30 20 10 0 l Measure at the bottom of the meniscus.

45. How to Measure Volume l Always be level with the meniscus to avoid parallax errors Correct: Viewing the meniscus at eye level Incorrect: viewing the meniscus from an angle

46. How to Measure Volume l Read the volume using all certain digits and one uncertain digit. l Certain digits are determined from the calibration marks on the cylinder. l The uncertain digit (the last digit of the reading) is estimated.

47. How to Measure Volume Use the graduations to find all certain digits There are two unlabeled graduations below the meniscus, and each graduation represents 1 mL, so the certain digits of the reading are… 52 mL.

48. How to Measure Volume Estimate the uncertain digit and take a reading The meniscus is about eight tenths of the way to the next graduation, so the final digit in the reading is. The volume in the graduated cylinder is 0.8 mL 52.8 mL.

49. 48 Measuring Temperature l Same as volume – read to the calibration marks and then estimate the last digit l Do not allow the thermometer to touch the walls or bottom of the beaker, etc. when measuring temperature 0ºC

50. 49 Reading the Thermometer _ _. _  C 874350

51. 50 Mass l Quantity of matter in an object l WEIGHT – depends on gravity l Massing an object often called “weighing” b/c weight is proportional to mass

52. 51 Measuring Mass l Analytical balance3-beam balance

53. How to measure Mass 1002004003005000 0102030405060708090 012345678910

54. 53 Measuring Mass  Always check that the balance is level and zeroed before using it.  Never weigh chemicals directly on the balance pan. Always use a weighing boat or a dish.  Do not weigh extremely hot or cold objects.

55. 54 The Metric System

56. 55 Measuring l Numbers without units are meaningless. l “It is 10 long.” l 10 what?

57. 56 The Metric System l Easier to use b/c it’s a decimal system. –Every conversion is by some power of 10. l A metric unit has two parts - a prefix and a base unit. –Prefix tells you how many times to divide or multiply by 10.

58. 57

59. 58 The International System of Units (SI) l Most common base units –meter (m) - length –gram (g) – mass –Liter (L) – volume –Kelvin (K) – temperature K = °C + 273 –second (s) - time –mole (mol) – amount of substance

60. 59 Common Metric Prefixes l Mega (M) = 10 6 l ** Kilo (k) = 10 3 l ** Deci (d) = 10 -1 l ** Centi (c) = 10 -2 l ** Milli (m) = 10 -3 l Micro (µ) = 10 -6 l Nano (n) = 10 -9 l Pico (p) = 10 -12

61. 60 Converting with a ladder khDdcm The box is the base unit (meters, Liters, grams, etc.) 1. Find your starting unit 2. Count the steps to your end unit. 3. The direction you move is the direction you move the decimal.

62. 61 Conversions with a ladder l Change 5.6 m to millimeters khDdcm l Starts at the base unit and moves three to the right. l So…move the decimal point three to the right 5600

63. 62 Conversions with a ladder l Convert 25 mg to grams l Convert 0.45 km to mm l Convert 35 mL to liters khDdcm

64. 63 Conversions with a ladder l Only works with same base unit –m to cm –kg to mg l So what do we do if the units are different or don’t use the decimal system? –Feet to inches –Meters to miles

65. 64 Conversion factors l A ratio of equivalent measurements. l 1 m = 100 cm l Or write it as a ratio 1 m OR 100 cm 100 cm 1 m l Conversion factor is equal to 1

66. 65 Dimensional Analysis l Easy way to convert units – even if it’s NOT a decimal system l Make sure your units cancel out l Calculate like a fraction

67. 66 EXAMPLE l 13 inches is how many yards? l 36 inches = 1 yard l 13 inches1 yard = 13 = 0.36 yards 36 inches 36

68. 67 Dimensional Analysis l Really just multiplying by one, in a creative way. l Choose the conversion factor that gets rid of the unit you don’t want.

69. 68 Dimensional Analysis l A ruler is 12.0 inches long. How long is it in cm? ( 1 inch is 2.54 cm) l in meters? l A race is 10.0 miles long. How far is this in yards? – 1 mile = 1760 yards l Pikes Peak is 14,110 ft above sea level. What is this in meters? –1 meter = 3.28 feet

70. 69 Multiple Units l 25 kg = _____ mg 25 kg1000 g 1 kg 1000 mg 1 g 25, 000, 000 mg = 2.5 x 10 7 mg

71. 70 Multiple units l The speed limit is 65 mi/hr. What is this in m/s? –1 mile = 1760 yds – 1 meter = 1.094 yds 65 mi hr 1760 yd 1 mi1.094 yd 1 m1 hr 60 min 1 min 60 s

72. 71 Density l The ratio of mass to volume l D = m / V l Density is the same no matter the sample size so it can be used to help identify unknown substances

73. 72 Calculating l D = m/V l Units will be g/mL or g/cm 3 l 1 mL = 1 cm 3 l A piece of wood has a mass of 11.2 g and a volume of 23 mL. What is the density?

74. 73 Calculating l A piece of wood has a density of 0.93 g/mL and a mass of 23 g. What is the volume? l Return to Algebra 1 l What ever you do to one side, do to the other. l How would you find the density in kg/L?

75. 74 m DV

76. 75 Floating l Lower (less) density floats on higher (more) density. l Ice is less dense than water (Atypical) l Most wood is less dense than water. l Helium is less dense than air. l A ship is less dense than water.