Significant Figures

1. Significant Figures

2. Laboratory measurements are made by reading all digits on the instrument, and estimating one digit.

3. Significant Figures • All the digits of a measurement that you are sure of (markings on the instrument) plus one estimated digit.

4. Significant Figures • Used to express limitations in a measurement.

5. Rules for significant digits. • Nonzero digits are always significant. • Example: 5.67 • All final zeros used after the decimal point are significant. • Example: 5.60 • Zeros between two other significant digits are always significant. • Example: 5006, 5.006 • Zeros used solely for spacing the decimal point are not significant. • Example: 56,100 , 0.566 , .0561

6. Significant zerosIf a zero is used only to place the decimal, it is NOT significant. Examples: • Desk measures 32.10 cm • What is the last marking on the instrument? • How many significant figures in this number. • Counting numbers are exact whole numbers. • 30 people in the room • $20.05 dollars in my pocket

7. Reading a Measurement A) 720.29g B) 722.9 g C.) 722.90 g D.) 723 g

8. Reading a Measurement A.) 200 g B.) 200.5 g C.) 200.55 g D.) 20.5g

9. Reading a Measurement A.) 76.0 ml B.) 76 ml C.) 77 ml D.) 75.00 ml

10. Reading a Measurement A.) 47 ml B.) 47.00 ml C.) 47.0 ml D.) 44 ml

11. Reading a Measurement A.) 3.44 ml B.) 3.4 ml C.) 3.50 ml D.) 3.5 ml E.) 3.48 ml

12. Lec Sup #1 How many significant figures are in the measurement 405cm? 0 1 2 3 4

13. Lec Sup #2 How many significant figures are in the measurement 3.208 cm? 0 1 2 3 4

14. Lec Sup #3 How many significant figures are in the measurement 3000 cm? 0 1 2 3 4

15. Lec Sup #4 How many significant figures are in the measurement .0045 cm? 0 1 2 3 4

16. Lec Sup #5 How many significant figures are in the measurement .0450 cm? 0 1 2 3 4

17. Rules for calculating with significant figures. Addition or subtraction Your final answer may contain no more places after the decimal than your least known quantity. (Round the answer so that it has the same number of decimal places as the measurement having the fewest decimal places.)

18. Example: 42.253 mL 125.6 mL1.75 mL 169.603 mL *Answer can only have as many places to the right of the decimal as that of the known quantity with the least:= 169.6 mL

19. Multiplication and divisionYour final answer may have no more total Significant digits than your known quantity with the least number of significant figures. Example: 62 cm x 33.03 cm = 2047.86 cm2 *only good to 2 figs 2.0 x 10 3 cm2

20. Rules for rounding off Look at digit to the right of digit to be rounded.IF: • Greater than or equal to 5 round up, less than 5 leave.

21. Lec Sup #6Round to three significant figures. A) 8.7300 B) 8.7200 C) 8.72 D) 8.73 E.) 8.73 X 104 • 8.7257cm =

22. Lec Sup #7Round to three significant figures. A) 126.00 B) 125 C) 126 D) 125.00 E.) 130. • 125.699cm =

23. Lec Sup #8Round to three significant figures. A) 124 B) 124,000 C) 120,000 D) 1.20 X 104 E.) 125,000 • 124,292 =

24. Lec Sup #9 Example: • If 4.383 g of oxygen • combine with 0.0023 g of carbon, • what’s the mass of the resulting compound? 4.4 g 4.38 g 4.385 g 4.3853 g 4.39 g 4.383 g 0.0023 g 4.3853 g

25. Lec Sup #10 Example: • If a line of 1.0 x 108 water molecules is 1.00 inches long, what is the average diameter, in millimeters of a water molecule? 1.00 inch 2.54 cm 1 m 1000 mm 1.0 x 108 molecules 1 inch 100 cm 1 m = 2.54 x 10-7 = 2.5 x 10-7 mm/molecule

26. Lec Sup #11 • A student places 28.70 g of iron, • 0.3807 oz of aluminum, and 0.00389 lb of • copper in a beaker that weighs 138 g. • What is the total mass in grams of the • beaker and its contents? • 179.27 g • 179.3 g • 179 g • 180 g • 200 g Note: conversions will count in sig fig analysis if the conversion is not exact. For instance metric to english (1lb is approx 454 g). But not in the case of exact conversions (1 lb is exactly 16 oz

27. #11 • A student places 28.70 g of iron, • 0.3807 oz of aluminum, and 0.00389 lb of • copper in a beaker that weighs 138 g. • What is the total mass in grams of the • beaker and its contents? 0.3807 oz 1.00 lb 454 g 16 oz 1.00 lb 28.70 g 10.8 g 1.77 g 138 g 179.27 = 179 g = 10.8 gAl 0.00389 lb 454 g 1.00 lb = 1.77 gCu

28. Lec Sup #12 • A girl needs to reflux a mixture • for 9.85 hours. How long must • the mixture reflux in minutes? = 591 min = 600 min = 590 min 9.85 h 60 min 1 h

29. Lec Sup #12 • A girl needs to reflux a mixture • for 9.85 hours. How long must • the mixture reflux in minutes? Exact conversions do not dictate the number of significant figures in answer since infinitely significant. 9.85 h 60 min 1 h

30. Lec Sup #13 • A group of chemistry students are instructed to measure a 0.75 m length of magnesium ribbon and a .100m length of ribbon. How long will the total ribbon be in mm? • .850mm • 850mm • 8.50 X 102 mm If multiple operations, calc sig figs through order of operations to see how answer should be reported.

31. A group of chemistry students are instructed to measure a 0.75 m length of magnesium ribbon and a .100m length of ribbon. How long will the total ribbon be in mm? 0.75 m + .100m = .85m .85m 1000 mm 1 m = 850 mm

32. Accuracy & Precision Accuracy: how close a measurement is to the true value of the quantity that was measured. Precision: (1) how closely two or more measurements of the same quantity agree with one another as well as (2) the degree of exactness.

33. Classification of Matter • Chemistry: • Study of matter and changes in matter • Matter • Anything that occupies space and has mass

34. Pure Substance: • Form of matter that has a constant composition and distinct properties. • Mixture: • Combination of 2 or more substances in which the substances retain their distinct identities.

35. Types of Mixtures • Homogeneous: • Composition of mixture is the same throughout. (solutions) • Heterogeneous: • Composition is not uniform (suspensions)

36. Types of Pure Substances • Element: • Substance which cannot be separated into simpler substances by chemical means. • Compound: • Composed of atoms of 2 or more elements chemically fixed in definite proportions. Na, K, Cl C6H12O6

37. Classification of Matter

38. Example 14:Classify Dry Ice as one of the following (a) an element, (b) a compound, (c) or a mixture:

39. Example14:Classify gasoline as one of the following (a) an element, (b) a compound, (c) or a mixture:

40. Example 14:Classify air as one of the following (a) an element, (b) a compound, (c) or a mixture:

41. Example 14:Classify blood as one of the following (a) an element, (b) a compound, (c) or a mixture:

42. Example 14:Classify methane as one of the following (a) an element, (b) a compound, (c) or a mixture:

43. Example 14:Classify Iodine as one of the following (a) an element, (b) a compound, (c) or a mixture:

44. Similar properties on the periodic table • Families(groups)/Periods • Oxidation numbers • Polyatomic ions • metals, nonmetals, and metalloids

45. Chemical Physical Extensive Intensive Macroscopic Microscopic Types of Properties

46. Lec Supplement 15: The following are properties of the element silicon; classify them as(a) physical intensive, (b) physical extensive, (c) or chemical properties: • _______ Melting point, 1410oC

47. Lec Supplement 15: The following are properties of the element silicon; classify them as(a) physical intensive, (b) physical extensive, (c) or chemical properties: • _______ Reacts with fluorine to form • silicon tetrafluoride

48. Lec Supplement 15: The following are properties of the element silicon; classify them as(a) physical intensive, (b) physical extensive, (c) or chemical properties: • _______ Gray

49. Lec Supplement 15: The following are properties of the element silicon; classify them as(a) physical intensive, (b) physical extensive, (c) or chemical properties: • _______ Not affected by most acids

50. Matter Changes • Physical change: does not change the identity (composition) of substance • Chemical change: changes chemical composition (identity of substance) • both involve energy transformation • endothermic: absorb energy • exothermic: release energy