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Introduction to Chemistry

Introduction to Chemistry. CHEMISTRY = Chemistry is the study of matter and energy and the interactions between them. Observations. Studying science requires that one be a good observer. observation inference. uses the five senses. involves a judgment or assumption. Data.

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Introduction to Chemistry

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  1. Introduction to Chemistry CHEMISTRY = Chemistry is the study of matter and energy and the interactions between them

  2. Observations Studying science requires that one be a good observer. observation inference uses the five senses involves a judgment or assumption

  3. Data There are two types of data. Observations are also called data. qualitative data quantitative data descriptions; measurements; no numbers must have numbers and UNITS

  4. How good are the measurements? • Scientists use two word to describe how good the measurements are- • Accuracy- how close the measurement is to the actual value. • Precision- how well can the measurement be repeated.

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

  6. PRECISION VERSUS ACCURACY Problem : Identify if the following figures are either accurate or precise or both: • A._________ B._________ C.__________ D._________ Only Precise Neither A/P A ? Both A & P

  7. In terms of measurement • Three students measure the room to be 10.2 m, 10.3 m and 10.4 m across. • Were they precise? • Were they accurate?

  8. Data • Must be organized • Can be organized into charts, tables, or graphs

  9. Line Graph shows continuous change Stock Price over Time

  10. Elements of a “good” line graph • axes labeled, with units • use the available space • title • neat

  11. How to read a graph • Interpolate - read between data points • What volume would the gas occupy at a temperature of 150 K? • Extrapolate - read data beyond data points • What volume would the gas occupy at a temperature of 260 K? • Which do you have more confidence in? Why? 7 L (dependent variable) ~4 L (independent variable)

  12. Line Graph How does the mass of a penny change with age? B A Mass (g) Mass (g) Age (Year of Penny) Age (Year of Penny) D C Mass (g) Mass (g) Age (Year of Penny) Age (Year of Penny)

  13. Hypothesis • A suggested solution to the problem. • Must be testable • Sometimes written as If…Then… statements • Predicts an outcome

  14. A law states what happens. Scientific Law vs. Scientific Theory A theory tries to explain why or how something happens. Law of Gravity Theory of Gravity Atomic Theory Collision Theory of Reactions

  15. Significant Figures Numbers in science are used to measure Measurements can only be taken to the least precise level of the measuring device

  16. Significant Figures Counting Sig Fig Examples 1. 23.50 1. 23.50 4 sig figs, rule # 3 sig figs, rule # 2. 402 2. 402 3. 5,280 3. 5,280 3 sig figs , rule # 2 sig figs , rule # 4. 0.080 4. 0.080 Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  17. Rounding rules • Look at the number behind the one you’re rounding. • If it is 0 to 4 don’t change it. • If it is 5 to 9 make it one bigger. • Round 45.462 to four sig figs. • to three sig figs. • to two sig figs. • to one sig figs. 45.46 45.5 45 50

  18. Watch the Sig Figs • When rounding, you don’t change the size of the number. • You should end up with a number about the same size (magnitude). • Use place holders- they’re not significant. • Round 15253 to 3 sig figs • Round 0.028965 to 3 sig figs 15300 0.0290

  19. Significant figures (cont’d) 98.748 __________ 950.9 __________ 0.08 __________ 0.058 __________ 8.097 __________ 74.99 __________ Round to the tenths Round to the hundredths

  20. Significant Figures # of sig figs in the answer is based on the # sig figs in least precise measurement. Which is the least precise? 7.22m or 7.22555 m Calculating with Sig Figs

  21. Significant Figures Calculating with Sig Figs • Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer. • (This is the measurement that is the LEAST precise) 224 g + 130 g 354 g 224 g + 130 g 354 g 3.75 mL + 4.1 mL 7.85 mL 3.75 mL + 4.1 mL 7.85 mL  350 g  7.9 mL Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  22. 3 SF Significant Figures Calculating with Sig Figs • Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer. • (This is the measurement that is the LEAST precise) (13.91g/cm3)(23.3cm3) = 324.103g 4 SF 3 SF 324g Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

  23. Measuring with Accuracy and Precision

  24. 1 2 3 4 5 0 cm 1 2 3 4 5 0 cm 1 2 3 4 5 0 cm Practice Measuring Length 4.5 cm 4.54 cm 3.0 cm Timberlake, Chemistry 7th Edition, page 7

  25. 0 100 200 300 400 500 0 1 2 3 4 5 6 7 8 9 10 How to measure Mass 0 10 20 30 40 50 60 70 80 90

  26. How to Measure Volume 50 Graduated Cylinder Come in variety of sizes measure milliliters 40 30 20 10 0

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

  28. The units of measurement in science are from the metric system. • The three most common are mass (grams), volume (liters), and length (meters) • The metric system utilizes these base units then adds prefixes to indicate values increasing or decreasing by a factor of 10. The Metric System

  29. k h D d c m Converting • how far you have to move on this chart, tells you how far, and which direction to move the decimal place. • The box is the base unit, meters, Liters, grams, etc. . . . . . . .

  30. k h D d c m Converting . . . . . . . • In order to convert from one unit to another, set up a proportion where the unknown (X) and the given (G) with their respective units of measurement are on top and the conversion factors are under in the right place.

  31. Metric Conversions 10cm = _____m 1mm = _____cm 10dL = _____mL 5 liters = _____mL

  32. Metric Conversions 0.1dL = _____cL 1Kg = _____g 100 mm = _____cm 300,00mg = _____g

  33. h D d c m k 3 3 What about micro- and nano-? . . . . . . . . . μ n • The jump in between is 3 places • Convert 15000 μm to m • Convert 0.00035 cm to nm

  34. Scientific Notation

  35. How wide is our universe? 210,000,000,000,000,000,000,000 miles (22 zeros) This number is written in decimal notation. When numbers get this large, it is easier to write them in scientific notation.

  36. Powers of 10 • http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/ • http://www.powersof10.com/

  37. Scientific Notation A number is expressed in scientific notation when it is in the form a x 10n where a is between 1 and 10 and n is an integer

  38. Write the width of the universe in scientific notation. 210,000,000,000,000,000,000,000 miles Where is the decimal point now? After the last zero. Where would you put the decimal to make this number be between 1 and 10? Between the 2 and the 1

  39. 2.10,000,000,000,000,000,000,000. How many decimal places did you move the decimal? 23 When the original number is more than 1, the exponent is positive. The answer in scientific notation is 2.1 x 1023

  40. 1) Express 0.0000000902 in scientific notation. Where would the decimal go to make the number be between 1 and 10? 9.02 The decimal was moved how many places? 8 When the original number is less than 1, the exponent is negative. 9.02 x 10-8

  41. Write 28750.9 in scientific notation. • 2.87509 x 10-5 • 2.87509 x 10-4 • 2.87509 x 104 • 2.87509 x 105

  42. 2) Express 1.8 x 10-4 in decimal notation. 0.00018 3) Express 4.58 x 106 in decimal notation. 4,580,000 On the graphing calculator, scientific notation is done with the button. 4.58 x 106 is typed 4.58 6

  43. 4) Use a calculator to evaluate: 4.5 x 10-5 1.6 x 10-2 Type 4.5 -5 1.6 -2 You must include parentheses if you don’t use those buttons!! (4.5 x 10 -5) (1.6 x 10 -2) 0.0028125 Write in scientific notation. 2.8125 x 10-3

  44. 5) Use a calculator to evaluate: 7.2 x 10-9 1.2 x 102On the calculator, the answer is: 6.E -11 The answer in scientific notation is 6 x 10 -11 The answer in decimal notation is 0.00000000006

  45. 6) Use a calculator to evaluate (0.0042)(330,000).On the calculator, the answer is 1386. The answer in decimal notation is 1386 The answer in scientific notation is 1.386 x 103

  46. 7) Use a calculator to evaluate (3,600,000,000)(23).On the calculator, the answer is: 8.28 E +10 The answer in scientific notation is 8.28 x 10 10 The answer in decimal notation is 82,800,000,000

  47. Write (2.8 x 103)(5.1 x 10-7) in scientific notation. • 14.28 x 10-4 • 1.428 x 10-3 • 14.28 x 1010 • 1.428 x 1011

  48. Write in PROPER scientific notation.(Notice the number is not between 1 and 10) 8) 234.6 x 109 2.346 x 1011 9) 0.0642 x 104 on calculator: 642 6.42 x 10 2

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