Unit 2: Scientific Processes and Measurement

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 Measurement - quantitative observation consisting of 2 parts Part 1 - number Part 2 - scale (unit) Examples: • 20grams • 6.63 x 10-34Joule 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. Parallaxerrors arise when a meniscus or needle is viewed from an angle rather than from straight-on at eye level. Correct: Viewing the meniscusat eye level Incorrect: viewing the meniscusfrom 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 uncertaindigit. • 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 6 _ . _ _ mL 2

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

26. Self Test Examine the meniscus below and determine the volume of liquid contained in the graduated cylinder. The cylinder contains: 7 6 0 _ _ . _ mL

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: 8 7 4 3 5 0 _ _ . _ C _ _ . _ C

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 truevalue. Precisionrefers to the degree of agreement among several measurements made in the same manner. Precise but not accurate Precise AND accurate Neither accurate nor precise

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

41. Rules for Counting Significant Figures - Details • Zeros • Leading zeros do not count as significant figures. • 0.0486 has • 3 sig figs.

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

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

44. Rules for Counting Significant Figures - Details • Exact numbershave an infinite number of significant figures. • 1 inch = 2.54cm, exactly

45. Sig Fig Practice #1 How many significant figures in each of the following? 1.0070 m  5 sig figs 17.10 kg  4 sig figs 100,890 L  5 sig figs 3.29 x 103 s  3 sig figs 0.0054 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 22.68 m2 3.24 m x 7.0 m 23 m2 100.0 g ÷ 23.7 cm3 4.22 g/cm3 4.219409283 g/cm3 0.02 cm x 2.371 cm 0.05cm2 0.04742 cm2 710 m ÷ 3.0 s 236.6666667 m/s 240 m/s 5870 lb·ft 1818.2 lb x 3.23 ft 5872.786 lb·ft 2.9561 g/mL 2.96 g/mL 1.030 g ÷ 2.87 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. • 6.8 + 11.934 = • 18.734  18.7 (3 sig figs)

49. Sig Fig Practice #3 Calculation Calculator says: Answer 10.24 m 3.24 m + 7.0 m 10.2 m 100.0 g - 23.73 g 76.3 g 76.27 g 0.02 cm + 2.371 cm 2.39 cm 2.391 cm 713.1 L - 3.872 L 709.228 L 709.2 L 1821.6 lb 1818.2 lb + 3.37 lb 1821.57 lb 0.160 mL 0.16 mL 2.030 mL - 1.870 mL

50. Scientific Notation In science, we deal with some very LARGE numbers: 1 mole = 602000000000000000000000 In science, we deal with some very SMALL numbers: Mass of an electron = 0.000000000000000000000000000000091 kg