1. Unit 2: Scientific Processes and Measurement

2. Science: man made pursuit to understand natural phenomena
Chemistry: study of matter

3. Safety Resources Hazard Symbols blue – health red – flammability
yellow – reactivity white – special codes
Scale: 0 to 4
0 = no danger
4 = extreme danger!

4. MSDS – Material Safety Data Sheet
gives important information about chemicals
first aid, fire-fighting, properties, disposal, handling/storage, chemical formula…

5. Scientific Method
General set of guidelines used in an experiment

6. Hypothesis
Testable statement based on observations; can be disproven, but not proven

7. Which of these is a hypothesis that can be tested through experimentation?
A) Bacterial growth increases exponentially as temperature increases.
B) A fish’s ability to taste food is affected by the clarity of aquarium water.
C) Tadpoles’ fear of carnivorous insect larvae increases as the tadpoles age.
D) The number of times a dog wags its tail indicates how content the dog is.

8. Law States phenomena but does not address “why?”
Examples: Newton’s Laws of Motion, Law of Conservation of Mass

9. Theory Broad generalization that explains a body of facts
Summarizes hypotheses that have been supported through repeated testing

10. Qualitative Observations
Non-numerical descriptions in an experiment
Example: Color is blue…

11. Quantitative Observations
Observations that are numerical
Example: the mass is 9.0 grams

12. Parts of an Experiment
Independent Variable: variable that is being changed or manipulated by YOU
Dependent Variable: variable that responds to your change ---- what you see
Controlled Variables: variables that you keep the same

13. Control or Control Set-up: used for comparison; allows you to measure effects of manipulated variable
Directly proportional: when one variable goes up, the other also goes up
Indirectly proportional: when one variable goes up, the other goes down

14. The diagram shows different setups of an experiment to determine how sharks find their prey. Which experimental setup is the control?
A) Q
B) R
C) S
D) T

15. “DRY MIX” - way to remember definitions and graphing
DRY – dependent, responding, y-axis
MIX – manipulated, independent, x-axis

16. Nature of Measurement Part 1 - number Examples: 20 grams
Measurement - quantitative observation
consisting of 2 parts
Part 1 - number
Part 2 - scale (unit)
Examples:
20 grams
6.63 x Joule seconds

17. Measuring
Volume
Temperature
Mass

18. Reading the Meniscus
Always read volume from the bottom of the meniscus. The meniscus is the curved surface of a liquid in a narrow cylindrical container.

19. Try to avoid parallax errors.
Parallax errors arise when a meniscus or needle is viewed from an angle rather than from straight-on at eye level.
Correct: Viewing the meniscus at eye level
Incorrect: viewing the meniscus from an angle

20. Graduated Cylinders
The glass cylinder has etched marks to indicate volumes, a pouring lip, and quite often, a plastic bumper to prevent breakage.

21. Measuring Volume
Determine the volume contained in a graduated cylinder by reading the bottom of the meniscus at eye level.
Read the volume using all certain digits and one uncertain digit.
Certain digits are determined from the calibration marks on the cylinder.
The uncertain digit (the last digit of the reading) is estimated.

22. 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.

23. 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
0.8 mL
The volume in the graduated cylinder is
52.8 mL.

24. 10 mL Graduate
What is the volume of liquid in the graduate? 6
_ . _ _ mL 6 2

25. 100mL graduated cylinder 5 _ _ . _ mL 2 7
What is the volume of liquid in the graduate? 5
_ _ . _ mL 2 7

26. The cylinder contains:
Self Test
Examine the meniscus below and determine the volume of liquid contained in the graduated cylinder.
The cylinder contains: 7
_ _ . _ mL 6

27. The Thermometer
Determine the temperature by reading the scale on the thermometer at eye level.
Read the temperature by using all certain digits and one uncertain digit.
Certain digits are determined from the calibration marks on the thermometer.
The uncertain digit (the last digit of the reading) is estimated.
On most thermometers encountered in a general chemistry lab, the tenths place is the uncertain digit.

28. Do not allow the tip to touch the walls or the bottom of the flask.
If the thermometer bulb touches the flask, the temperature of the glass will be measured instead of the temperature of the solution. Readings may be incorrect, particularly if the flask is on a hotplate or in an ice bath.

29. Reading the Thermometer
Determine the readings as shown below on Celsius thermometers:
_ _ . _ C 8 7 4
_ _ . _ C 3 5

30. Measuring Mass - The Beam Balance
Our balances have 4 beams – the uncertain digit is the thousandths place ( _ _ _ . _ _ X)

31. Balance Rules
In order to protect the balances and ensure accurate results, a number of rules should be followed:
Always check that the balance is level and zeroed before using it.
Never weigh directly on the balance pan. Always use a piece of weighing paper to protect it.
Do not weigh hot or cold objects.
Clean up any spills around the balance immediately.

32. Mass and Significant Figures
Determine the mass by reading the riders on the beams at eye level.
Read the mass by using all certain digits and one uncertain digit.
The uncertain digit (the last digit of the reading) is estimated.
On our balances, the hundredths place is uncertain.

33. Determining Mass 1. Place object on pan
2. Move riders along beam, starting with the largest, until the pointer is at the zero mark

34. Check to see that the balance scale is at zero

35. 1 1 4
? ? ?
_ _ _ . _ _ _
Read Mass

36. 1 1 4 4 9 7
_ _ _ . _ _ _
Read Mass More Closely

37. Uncertainty in Measurement
A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.

38. Why Is there Uncertainty?
Measurements are performed with instruments
No instrument can read to an infinite number of decimal places
Which of these balances has the greatest uncertainty in measurement?

39. Precision and Accuracy
Accuracy refers to the agreement of a particular value with the true value.
Precision refers to the degree of agreement among several measurements made in the same manner.
Neither accurate nor precise
Precise but not accurate
Precise AND accurate

40. Rules for Counting Significant Figures - Details
Nonzero integers always count as significant figures.
3456 has
4 sig figs.

41. Rules for Counting Significant Figures - Details
Zeros
Leading zeros do not count as
significant figures.
has
3 sig figs.

42. Rules for Counting Significant Figures - Details
Zeros
Captive zeros always count as
significant figures.
16.07 has
4 sig figs.

43. Rules for Counting Significant Figures - Details
Zeros
Trailing zeros are significant only if the number contains a decimal point.
9.300 has
4 sig figs.

44. Rules for Counting Significant Figures - Details
Exact numbers have an infinite number of significant figures.
1 inch = cm, exactly

45. Sig Fig Practice #1 1.0070 m  5 sig figs 17.10 kg  4 sig figs
How many significant figures in each of the following?
m 
5 sig figs
17.10 kg 
4 sig figs
100,890 L 
5 sig figs
3.29 x 103 s 
3 sig figs
cm 
2 sig figs
3,200,000 
2 sig figs

46. Rules for Significant Figures in Mathematical Operations
Multiplication and Division: # sig figs in the result equals the number in the least precise measurement used in the calculation.
6.38 x 2.0 =
12.76  13 (2 sig figs)

47. Sig Fig Practice #2 Calculation Calculator says: Answer 3.24 m x 7.0 m
100.0 g ÷ 23.7 cm3
g/cm3
4.22 g/cm3
0.02 cm x cm
cm2
0.05 cm2
710 m ÷ 3.0 s
m/s
240 m/s
lb x 3.23 ft
lb·ft
5870 lb·ft
1.030 g ÷ 2.87 mL
g/mL
2.96 g/mL

48. Rules for Significant Figures in Mathematical Operations
Addition and Subtraction: The number of decimal places in the result equals the number of decimal places in the least precise measurement. =
 18.7 (3 sig figs)

49. Sig Fig Practice #3 Calculation Calculator says: Answer 3.24 m + 7.0 m
100.0 g g
76.27 g
76.3 g
0.02 cm cm
2.391 cm
2.39 cm
713.1 L L L
709.2 L
lb lb lb lb
2.030 mL mL
0.16 mL
0.160 mL

50. Scientific Notation In science, we deal with some very LARGE numbers:
1 mole =
In science, we deal with some very SMALL numbers:
Mass of an electron = kg

51. Imagine the difficulty of calculating the mass of 1 mole of electrons!kg x
???????????????????????????????????

52. Scientific Notation:
A method of representing very large or very small numbers in the form:
M x 10n
M is a number between 1 and 10
n is an integer

53. . 9 8 7 6 5 4 3 2 1
Step #1: Insert an understood decimal point
Step #2: Decide where the decimal must end
up so that one number is to its left
Step #3: Count how many places you bounce
the decimal point
Step #4: Re-write in the form M x 10n

54. 2.5 x 109
The exponent is the number of places we moved the decimal.

55. 0.0000579 1 2 3 4 5 Step #2: Decide where the decimal must end
up so that one number is to its left
Step #3: Count how many places you bounce
the decimal point
Step #4: Re-write in the form M x 10n

56. 5.79 x 10-5
The exponent is negative because the number we started with was less than 1.

57. Review: M x 10n Scientific notation expresses a number in the form:
n is an integer
1  M  10

58. Calculator instructions
2 x 106 is entered as 2 2nd EE 6
EE means x 10
If you see E on your calculator screen, it also means x 10

59. Try…
2 x 1014 / 3 x 10-3 = ?
2 x x 3 x 1023
4.5 x 1023 / 5.26 x 10-14

60. The Fundamental SI Units (le Système International, SI)

61. Metric System Prefixes (use with standard base units)
Kilo KING
Hecta HENRY
Deca DIED
Unit UNEXPECTEDLY
Deci DRINKING
Centi CHOCOLATE
Milli MILK

62. Conversion Unit Examples
1 L = 1000 mL 1 Hm = ______ m
1 m = ____ cm 1 Dm = _____ m
1 kg = 1000 g ___ dm = 1 m

63. Metric System Prefixes (use with standard base units)
Tera ,000,000,000,000 THE
Giga 109 1,000,000,000 GREAT
Mega 106 1,000,000 MIGHTY
Kilo KING
Hecta HENRY
Deca DIED
Unit UNEXPECTEDLY
Deci DRINKING
Centi CHOCOLATE
Milli MILK
Micro MAYBE
Nano NOT
Pico PASTUERIZED?

64. Conversion Unit Examples
1 L = 1000 mL 1 m = ______ nm
1 m = ____ cm 1 Dm = _____ m
1 kg = 1000 g ___ dm = 1 m
1 Mm = _____ m 1 Gb = _____ byte