1. Chapter 1: Scientists’ Tools

2. Chemistry is an Experimental Science This chapter will introduce the following tools that scientists use to “do chemistry”  Section 1.1: Observations & Measurements  Section 1.2: Converting Units  Section 1.3: Significant Digits  Section 1.4: Scientific Notation

3. Section 1.1—Observations & Measurements

4. Taking Observations Qualitative descriptions  Color  Texture  Formation of solids, liquids, gases  Heat changes  Anything else you observe

5. Clear versus Colorless Clear See-through Cloudy Parts are see- through with solid “cloud” in it Opaque Cannot be seen through at all Colorless does not describe transparency Words to describe transparency  You can be clear & colored  You need to describe the color of the solution & the cloud if it’s cloudy (examples: blue solution & white cloud or colorless solution and blue solid)

6. Clear versus Colorless Cherry Kool-ade Example: Describe the following in terms of transparency words & colors Whole Milk Water

7. Clear versus Colorless Cherry Kool-adeClear & red Example: Describe the following in terms of transparency words & colors Whole Milk Water Opaque & white Clear & Colorless

8. Gathering Data Quantitative measurements International System of Units (SI Units) are used Quantity Mass (how much stuff is there) Unit Kilogram (kg) Instrument used Balance Volume (how much space it takes up) Liters (L) Graduated cylinder Temperature (how fast the particles are moving) Kelvin (K) or Celsius (°C) Thermometer Length Meters (m) Meter stick Time Seconds (sec) stopwatch Energy Joules (J) (Measured indirectly)

9. Measurement tool for Mass

10. Measurement Tool for Temperature

11. Uncertainty in Measurement Every measurement has a degree of uncertainty The last decimal you write down is an estimate  Write down a “5” if it’s in-between lines  Write down a “0” if it’s on the line 5 mL 10 15 20 25 mL 5 mL 10 15 20 25 mL Remember: Always read liquid levels from the bottom of the meniscus (the bubble at the top) Example: Read the measurements

12. Uncertainty in Measurement Every measurement has a degree of uncertainty The last decimal you write down is an estimate  Write down a “5” if it’s in-between lines  Write down a “0” if it’s on the line 5 mL 10 15 20 25 mL 5 mL 10 15 20 25 mL Example: Read the measurements It’s in- between the 10 & 11 line 10.5 mL It’s on the 12 line 12.0 mL

13. Measurement Tool for Volume

14. Measurement Tool for Length 1.5 cm 1.95 cm

15. Uncertainty in Measurement Example: Read the measurements 1234567812345678

16. Uncertainty in Measurement Example: Read the measurements 1234567812345678 It’s right on the 6.9 line 6.90 It’s between the 3.8 & 3.9 line 3.85

17. HINT:Uncertainty in Measurement Choose the right instrument  If you need to measure out 5 mL, don’t choose the graduated cylinder that can hold 100 mL. Use the 10 or 25 mL cylinder The smaller the measurement, the more an error matters—use extra caution with small quantities  If you’re measuring 5 mL & you’re off by 1 mL, that’s a 20% error  If you’re measuring 100 mL & you’re off by 1 mL, that’s only a 1% error

18. Gathering Data Multiple trials help ensure that you’re results weren’t a one-time fluke! Precise—getting consistent data (close to one another) Accurate—getting the “correct” or “accepted” answer consistently Example: Describe each group’s data as not precise, precise or accurate Correct value

19. Precise & Accurate Data Example: Describe each group’s data as not precise, precise or accurate Correct value Precise, but not accurate Precise & Accurate Not precise

20. Can you be accurate without precise? Correct value This group had one value that was almost right on…but can we say they were accurate? No…they weren’t consistently correct. It was by random chance that they had a result close to the correct answer.

21. Can you be accurate without precise? Correct value This group had one value that was almost right on…but can we say they were accurate?

22. You Try! Accepted Value = bulls-eye *not accurate but precise *accurate & precise *not precise nor accurate

23. Example: Below is a data table produced by three groups of students who were measuring the mass of a paper clip which had a known mass of 1.0004g. Group 1Group 2Group 3Group 4 1.01 g2.863287 g10.13251 g2.05 g 1.03 g2.754158 g10.13258 g0.23 g 0.99 g2.186357 g10.13255 g0.75 g Average1.01 g2.601267 g10.13255 g1.01 g

24. Percent Error A calculation designed to determine accuracy % Error = |Accepted - Experimental| x 100 |Accepted|

25. You Try! A student measured an unknown metal to be 1.50 grams. The accepted value is 1.87 grams. What is the percent error? % Error = |1.87 –1.50| x 100 1.87 = 20%

26. Section 1.2—Converting Units

27. Converting Units Often, a measurement is more convenient in one unit but is needed in another unit for calculations. Dimensional Analysis is a method for converting unit

28. Equivalents Dimensional Analysis uses equivalents…called Conversion Factors 1 foot = 12 inches or 4 quarters = 1 dollar What happens if you put one on top of the other? 1 foot 12 inches 4 quarters 1 dollar

29. Equivalents Dimensional Analysis uses equivalents called conversion factors…what are they? 1 foot = 12 inches What happens if you put one on top of the other? 1 foot 12 inches When you put two things that are equal on top & on bottom, they cancel out and equal 1 = 1

30. Dimensional Analysis Dimensional analysis is based on the idea that you can multiply anything by 1 as many times as you want and you won’t change the physical meaning of the measurement! 27 inches 1  = 27 inches

31. Dimensional Analysis Dimensional analysis is based on the idea that you can multiply anything by 1 as many times as you want and you won’t change the physical meaning of the measurement! 1 foot 12 inches = 2.25 feet 27 inches  1  = 27 inches

32. Dimensional Analysis Dimensional analysis is based on the idea that you can multiply anything by 1 as many times as you want and you won’t change the physical meaning of the measurement! 1 foot 12 inches = 2.25 feet 27 inches  Remember…this equals “1” 27 inches 1  = 27 inches Same physical meaning…it’s the same length either way!

33. Canceling Anything unit that is identical on the top and the bottom of an expression will cancel When canceling units…just cancel the units… 1 foot 12 inches 27 inches 

34. Common Equivalents 1 ft 12 in 1 in 2.54 cm 1 min 60 s 1 hr 3600 s 1 quart (qt) 0.946 L 4 pints 1 quart 1 pound (lb) 454 g = = = = = = =

35. Steps for using Dimensional Analysis 1 Write down your given information 2 Write down an answer blank and the desired unit on the right side of the problem space 3 Use conversion factors to cancel unwanted unit and get desired unit. 4 Calculate the answer…multiply across the top & divide across the bottom of the expression

36. Example #1 Example: How many grams are equal to 1.25 pounds? 1.25 lb 1 Write down your given information

37. Example #1 Example: How many grams are equal to 1.25 pounds? 1.25 lb 2 Write down an answer blank and the desired unit on the right side of the problem space = ________ g

38. Example #1 Example: How many grams are equal to 1.25 pounds? 1.25 lb = ________ g 3 Use equivalents to cancel unwanted unit and get desired unit. The equivalent with these 2 units is: 1 lb = 454 g A tip is to arrange the units first and then fill in numbers later!  lb g Put the unit on bottom that you want to cancel out! 1 454

39. Example #1 Example: How many grams are equal to 1.25 pounds? 1.25 lb = ________ g  lb g 1 454 4 Calculate the answer…multiply across the top & divide across the bottom of the expression Enter into the calculator: 1.25  454  1 568

40. Metric Prefixes  Metric prefixes can be used to form conversion factors as well  First, you must know the common metric prefixes used in chemistry

41. Metric Prefixes hecto- (h) 100 deci- (d) 0.1 centi- (c) 0.01 milli- (m) 0.001 micro- ( μ) 0.000001 nano (n) 0.000000001 = = = = = = BASE UNITS: These prefixes work with any base unit, such as grams (g), liters (L), meters (m), seconds (s), etc. kilo- (K) 1000 10 deka- (da) Base (1)  0.000000000001pico (p) mega- (M) giga- (G) tera- (T) 1,000,000 1,000,000,000 1,000,000,000,000 = = = = = =

42. Converting with the Metric System By Moving a Decimal Point From Kilo to Milli: Locate the known prefix and the one you need to convert to on the chart. Move the direction and the number of places it takes to go from the known to the other. If using the other prefixes, remember that there is a difference of 1000 or 3 places between each.

43. Examples Convert 15 cl into ml Convert 6000 mm into Km Convert 1.6 Dag into dg Convert 3.4 nm into m 150 ml.006 Km 160 dg.0000000034 m

44. Metric Activity: Answers 5 pm 4 x10 -9 m & 4 nm 1 x 10 -6 m 4 x 10 -3 m 10 mm & 1 cm 1m 5 km & 5 x 10 3 1Mm 1Gm

45. Metric Conversion Factors Many students get confused where to put the number shown in the previous chart… 1.Select which unit is greater. 2.Make that unit 1 and then determine how many smaller units are in the bigger unit. 1 kg = 1000 g my way OR.001Kg = 1 g the other way Example: Write a correct equivalent between “kg” and “g”

46. Try More Metric Equivalents There are two options: 1 L = 1000 ml my way 0.001 L = 1 mL the other way Example: Write a correct equivalent between “mL” and “L” There are two options: 1 cm = 10 mm my way.1cm = 1mm the other way Example: Write a correct equivalent between “cm” and “mm”

47. Metric Volume Units To find the volume of a cube, measure each side and calculate: length  width  height length height width But most chemicals aren’t nice, neat cubes! Therefore, they defined 1 milliliter as equal to 1 cm 3 (the volume of a cube with 1 cm as each side measurement) 1 cm 3 1 mL =

48. Example #2: Using D.A. Example: How many grams are equal to 127.0 mg? 127.0 mg = ________ g You want to convert between mg & g 1 g = 1000 mg my way 1 mg = 0.001 g the other way

49. Example #2 Example: How many grams are equal to 127.0 mg? 127.0 mg = ________ g  mg g 1000 1 Enter into the calculator: 127.0  0.001  1 0.1270 You may be able to do this in your head…but practice the technique on the more simple problems so that you’ll be a dimensional analysis pro for the more difficult problems (like stoichiometry)!

50. Multi-step problems There isn’t always an equivalent that goes directly from where you are to where you want to go! With multi-step problems, it’s often best to plug in units first, then go back and do numbers.

51. Example #3 Example: How many kilograms are equal to 345 cg? 345 cg = _______ kg There is no direct equivalent between cg & kg With metric units, you can always get to the base unit from any prefix! And you can always get to any prefix from the base unit! You can go from “cg” to “g” Then you can go from “g” to “kg”

52. 345 cg = _______ kg Example #3 Example: How many kilograms are equal to 345 cg?  cg g Go to the base unit  g kg Go from the base unit

53. = _______ kg Example #3 Example: How many kilograms are equal to 345 cg?  cg g 100 1 345 cg  g kg 1000 1 100 cg = 1 g 1000 g = 1 kg Remember—the # goes with the base unit & the “1” with the prefix!

54. = _______ kg Example #3 Example: How many kilograms are equal to 345 cg?  cg g 100 1 Enter into the calculator: (345  1 x 1)  (100 x 1000) 0.00345 345 cg  g kg 1000 1

55. You Try! #1 Example: 0.250 kg is equal to how many grams?

56. 1000 0.250 kg You Try! #1 Example: 0.250 kg is equal to how many grams? = ______ g  kg g 1 1 kg = 1000 g Enter into the calculator: 0.250  1000  1 250.

57. You Try! #2 Example: How many mL is equal to 2.78 L?

58. 1000 2.78 L You Try! #2 Example: How many mL is equal to 2.78 L? = ______ mL  L mL 1 1 mL = 0.001 L Enter into the calculator: 2.78  1000  1 2780

59. You Try! #3 Example: 147 cm 3 is equal to how many liters?

60. You Try! #3 Example: 147 cm 3 is equal to how many liters? Remember—cm 3 is a volume unit, not a length like meters! = _______ L  cm 3 mL 1 1 147 cm 3  mL L 1000 1 There isn’t one direct equivalent 1 cm 3 = 1 mL 1 L = 1000 mL or.001L = 1mL Enter into the calculator: 147  1  0.001  1  1 0.147

61. Let’s Practice #4 Example: How many milligrams are equal to 0.275 kg?

62. Let’s Practice #4 Example: How many milligrams are equal to 0.275 kg? = _______ mg  kg g 1 1000 0.275 kg  g mg 1 1000 There isn’t one direct equivalent 1 kg = 1000 g 1 g = 1000mg or 1 mg = 0.001 g Enter into the calculator: 0.275  1000  1000  1 275,000

63. Section 1.3—Significant Digits

64. Taking & Using Measurements You learned in Section 1.2 how to take careful measurements Most of the time, you will need to complete calculations with those measurements to understand your results 1.00 g 3.0 mL = 0.3333333333333333333 g/mL If the actual measurements were only taken to 1 or 2 decimal places… how can the answer be known to and infinite number of decimal places? It can’t!

65. Significant Digits A significant digit is anything that you measured in the lab—it has physical meaning The real purpose of “significant digits” is to know how many places to record in an answer from a calculation But before we can do this, we need to learn how to count significant digits in a measurement

66. Significant Digit Rules 1 All measured numbers are significant 2 All non-zero numbers are significant 3 Middle zeros are always significant 4 Trailing zeros are significant if there’s a decimal place 5 Leading zeros are never significant

67. All the fuss about zeros 102.5 g Middle zeros are important…we know that’s a zero (as opposed to being 112.5)…it was measured to be a zero 125.0 mL The convention is that if there are ending zeros with a decimal place, the zeros were measured and it’s indicating how precise the measurement was. 125.0 is between 124.9 and 125.1 125 is between 124 and 126 0.0127 m The leading zeros will dissapear if the units are changed without affecting the physical meaning or precision…therefore they are not significant 0.0127 m is the same as 127 mm

68. Sum it up into 2 Rules: Oversimplification Rule 1 If there is no decimal point in the number, count from the first non-zero number to the last non-zero number 2 If there is a decimal point (anywhere in the number), count from the first non-zero number to the very end The 4 earlier rules can be summed up into 2 general rules

69. Examples of Summary Rule 1 Example: Count the number of significant figures in each number 124 20570 200 150 1 If there is no decimal point in the number, count from the first non-zero number to the last non-zero number

70. Examples of Summary Rule 1 Example: Count the number of significant figures in each number 124 20570 200 150 1 If there is no decimal point in the number, count from the first non-zero number to the last non-zero number 3 significant digits 4 significant digits 1 significant digit 2 significant digits

71. Examples of Summary Rule 2 Example: Count the number of significant figures in each number 0.00240 240. 370.0 0.02020 2 If there is a decimal point (anywhere in the number), count from the first non-zero number to the very end

72. Examples of Summary Rule 2 Example: Count the number of significant figures in each number 0.00240 240. 370.0 0.02020 3 significant digits 4 significant digits 2 If there is a decimal point (anywhere in the number), count from the first non-zero number to the very end

73. Importance of Trailing Zeros Just because the zero isn’t “significant” doesn’t mean it’s not important and you don’t have to write it! “250 m” is not the same thing as “25 m” just because the zero isn’t significant The zero not being significant just tells us that it’s a broader range…the real value of “250 m” is between 240 m & 260 m. “250. m” with the zero being significant tells us the range is from 249 m to 251 m

74. Let’s Practice Example: Count the number of significant figures in each number 1020 m 0.00205 g 100.0 m 10240 mL 10.320 g

75. Let’s Practice Example: Count the number of significant figures in each number 1020 m 0.00205 g 100.0 m 10240 mL 10.320 g 3 significant digits 4 significant digits 5 significant digits

76. Performing Calculations with Sig Figs 1 Addition & Subtraction: Answer has least number of decimal places as appears in the problem 2 Multiplication & Division: Answer has least number of significant figures as appears in the problem When recording a calculated answer, you can only be as precise as your least precise measurement Always complete the calculations first, and then round at the end!

77. EXCEPTION: When adding/subtracting and then multiplying/dividing, follow the rules for addition/subtraction first and then apply that number of sig figs to the multiplication/division. (6.350- 6.010)/2.0 = _______

78. Addition & Subtraction Example #1 Example: Compute & write the answer with the correct number of sig digs 15.502 g + 1.25 g This answer assumes the missing digit in the problem is a zero…but we really don’t have any idea what it is 1 Addition & Subtraction: Answer has least number of decimal places as appears in the problem 16.752 g

79. Addition & Subtraction Example #1 Example: Compute & write the answer with the correct number of sig digs 15.502 g + 1.25 g 1 Addition & Subtraction: Answer has least number of decimal places as appears in the problem 16.752 g 16.75 g 3 decimal places 2 decimal places Lowest is “2” Answer is rounded to 2 decimal places

80. Addition & Subtraction Example #2 Example: Compute & write the answer with the correct number of sig digs 10.25 mL - 2.242 mL This answer assumes the missing digit in the problem is a zero…but we really don’t have any idea what it is 1 Addition & Subtraction: Answer has least number of decimal places as appears in the problem 8.008 mL

81. Addition & Subtraction Example #2 Example: Compute & write the answer with the correct number of sig digs 10.25 mL - 2.242 mL 1 Addition & Subtraction: Answer has least number of decimal places as appears in the problem 8.01 mL 2 decimal places 3 decimal places Lowest is “2” Answer is rounded to 2 decimal places 8.008 mL

82. Multiplication & Division Example #1 Example: Compute & write the answer with the correct number of sig digs 10.25 g 2.7 mL = 3.796296296 g/mL 2 Multiplication & Division: Answer has least number of significant figures as appears in the problem

83. Multiplication & Division Example #1 Example: Compute & write the answer with the correct number of sig digs 3.8 g/mL 4 significant digits 2 significant digits Lowest is “2” Answer is rounded to 2 sig digs 10.25 g 2.7 mL = 3.796296296 g/mL 2 Multiplication & Division: Answer has least number of significant figures as appears in the problem

84. Multiplication & Division Example #2 Example: Compute & write the answer with the correct number of sig digs 1.704 g/mL  2.75 mL 4.686 g 2 Multiplication & Division: Answer has least number of significant figures as appears in the problem

85. Multiplication & Division Example #2 Example: Compute & write the answer with the correct number of sig digs 4.69 g 4 significant dig 3 significant dig Lowest is “3” Answer is rounded to 3 significant digits 2 Multiplication & Division: Answer has least number of significant figures as appears in the problem 1.704 g/mL  2.75 mL 4.686 g

86. Let’s Practice #1 Example: Compute & write the answer with the correct number of sig digs 0.045 g + 1.2 g

87. Let’s Practice #1 Example: Compute & write the answer with the correct number of sig digs 1.2 g 3 decimal places 1 decimal place Lowest is “1” Answer is rounded to 1 decimal place 1.245 g Addition & Subtraction use number of decimal places! 0.045 g + 1.2 g

88. Let’s Practice #2 Example: Compute & write the answer with the correct number of sig digs 2.5 g/mL  23.5 mL

89. Let’s Practice #2 Example: Compute & write the answer with the correct number of sig digs 59 g 2 significant dig 3 significant dig Lowest is “2” Answer is rounded to 2 significant digits 2.5 g/mL  23.5 mL 58.75 g Multiplication & Division use number of significant digits!

90. Let’s Practice #3 Example: Compute & write the answer with the correct number of sig digs 1.000 g 2.34 mL

91. Let’s Practice #3 Example: Compute & write the answer with the correct number of sig digs 0.427 g/mL 4 significant digits 3 significant digits Lowest is “3” Answer is rounded to 3 sig digs 1.000 g 2.34 mL = 0.42735 g/mL Multiplication & Division use number of significant digits!

92. Let’s Practice #4 Example: Compute & write the answer with the correct number of sig digs 1.704 m  2.75 m

93. Let’s Practice #4 Example: Compute & write the answer with the correct number of sig digs 4.69 m 2 4 significant dig 3 significant dig Lowest is “3” Answer is rounded to 3 significant digits 1.704 m  2.75 m 4.686 g Multiplication & Division use number of significant digits!

94. Section 1.4—Scientific Notation

95. Scientific Notation Scientific Notation is a form of writing very large or very small numbers that you’ve probably used in science or math class before Scientific notation uses powers of 10 to shorten the writing of a number.

96. Writing in Scientific Notation The decimal point is put behind the first non-zero number The power of 10 is the number of times it moved to get there A number that began large (>1) has a positive exponent & a number that began small (<1) has a negative exponent

97. Example #1 Example: Write the following numbers in scientific notation. 12457.656 m 0.000065423 g 128.90 g 0.0000007532 m

98. Example #1 Example: Write the following numbers in scientific notation. 12457.656 m 0.000065423 g 128.90 g 0.0000007532 m 1.24567656  10 m 4 6.5423  10 g -5 1.2890  10 m 2 7.532  10 m -7 The decimal is moved to follow the first non-zero number The power of 10 is the number of times it’s moved

99. Tiny original numbers have negative exponents Example #1 Example: Write the following numbers in scientific notation. 12457.656 m 0.000065423 g 128.90 g 0.0000007532 m 1.24567656  10 m 4 6.5423  10 g -5 1.2890  10 m 2 7.532  10 m -7 Large original numbers have positive exponents

100. Reading Scientific Notation A positive power of ten means you need to make the number bigger and a negative power of ten means you need to make the number smaller Move the decimal place to make the number bigger or smaller the number of times of the power of ten

101. Example #2 Example: Write out the following numbers. 1.37  10 4 m 2.875  10 2 g 8.755  10 -5 g 7.005  10 -3 m

102. 1.37  10 4 m 2.875  10 2 g 8.755  10 -5 g 7.005  10 -3 m Example #2 Example: Write out the following numbers. 13700 m 287.5 g 0.00008755 m 0.007005 m Move the decimal “the power of ten” times Positive powers = big numbers. Negative powers = tiny numbers

103. Scientific Notation & Significant Digits Scientific Notation is more than just a short hand. Sometimes there isn’t a way to write a number with the needed number of significant digits …unless you use scientific notation!

104. Take a look at this… Write 120004.25 m with 3 significant digits 120004.25 m 120000. m 120000 m 1.20  10 5 m 120. m 8 significant digits 6 significant digits 2 significant digits 3 significant digits Remember…120 isn’t the same as 120000! Just because those zero’s aren’t significant doesn’t mean they don’t have to be there! This answer isn’t correct!

105. Let’s Practice Example: Write the following numbers in scientific notation. 0.0007650 g with 2 sig figs 120009.2 m with 3 sig figs 239087.54 mL with 4 sig figs 0.0000078009 g with 3 sig figs Example: Write out the following numbers 1.34 × 10 -3 g 2.009  10 -4 mL 3.987  10 5 g 2.897  10 3 m

106. Let’s Practice 7.7 × 10 -4 g 1.20 × 10 5 g 2.391 × 10 5 g 7.80 × 10 -6 g Example: Write the following numbers in scientific notation. 0.0007650 g with 2 sig figs 120009.2 m with 3 sig figs 239087.54 mL with 4 sig figs 0.0000078009 g with 3 sig figs Example: Write out the following numbers 1.34 × 10 -3 g 2.009  10 -4 mL 3.987  10 5 g 2.897  10 3 m 0.00134 g 0.0002009 mL 398700 g 2897 m