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Chapter 1 Chemical Foundations

Chapter 1 Chemical Foundations. CHY 115: General Chemistry I. Chapter Outline. Overview of chemistry Methods of science Measurements Unit systems Quantities measured Taking measurements Accuracy and precision, types of error Significant figures and calculations Dimensional analysis

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Chapter 1 Chemical Foundations

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  1. Chapter 1Chemical Foundations CHY 115: General Chemistry I

  2. Chapter Outline • Overview of chemistry • Methods of science • Measurements • Unit systems • Quantities measured • Taking measurements • Accuracy and precision, types of error • Significant figures and calculations • Dimensional analysis • Temperature • Density • Classification of matter

  3. Chemistry • Chemistry – study of the matter of the universe and the changes that this matter undergoes • Matter – anything that has mass and occupies space • Examples of matter and “non-matter”

  4. Chemistry • What chemists study about the matter: • Composition • Structure • Properties • Chemical changes the matter will undergo • Relationship between the matter and: • The environment • Human health

  5. Better living (?) through chemistry

  6. The Scientific Method (1.2) • The scientific method describes a framework by which science is conducted. • Scientific method has been described as organized common sense. • Methodical approach to problem-solving.

  7. Scientific Method • Observations  questions • Develop hypotheses to explain observations • Test hypotheses • Make predictions, if hypothesis is true then…. • Test accuracy of the prediction • Repeat the process, test new hypotheses… • Analyze results and share findings and conclusions

  8. Scientific Inquiry • Observations  Questions • Observations must be recordable and repeatable • Observations may be: • Quantitative or • Qualitative

  9. Scientific Inquiry • Develop and test hypotheses • Hypothesis – tentative explanation of the observations based on limited data • Make predictions based on the hypothesis • Test accuracy of the prediction • Data collected generates new observations which in turn, often leads to more hypotheses to test • Repeat for all hypotheses

  10. Scientific Inquiry • Analyze results and share findings and conclusions • Publish results in journals • Present findings at conferences….. • Public versus Private Research

  11. Types of Research • Basic research • scientific research for the sake of knowledge, no immediate application in mind. • Applied research •  scientific research with the short-term goal of solving a specific problem • begin the research with an application in mind.

  12. Theories • After significant research theories/models are developed to explain the observations • Theory – well-tested explanation of some part of nature that explains a broad range of observations • Supported by significant data • Subject to rigorous testing and revision when needed

  13. Natural Law versus Theory • Natural Law • Statement/summary of observed behavior • Law of conservation of matter • Theory (also called a model) • Explanation of observed behavior based on significant data • Theories attempt to explain laws

  14. Factors Impacting Scientific Inquiry • The direction of scientific research is impacted by many factors: • Theories and technology of the day • Money • Religion • Politics • World conditions

  15. Units of Measure (1.3) • Much of chemistry is based on analysis of quantitative observations • A quantitative observation is obtained by measurement and includes a number and a unit.

  16. Unit Systems • English system • Used in United States • Metric system • Used in science • International system (SI) • Based on the metric system UNITS MATTER!

  17. Unit Systems • English System • Used in U.S. • Little logic to the units • Examples

  18. Unit Systems • Metric System • Developed in the late 1700’s and adopted after the French Revolution • A base (or fundamental) unit is defined for each quantity measured • The size of the base unit can be modified by adding a prefix

  19. Unit Systems - metric Quantity Base unit Symbol

  20. Unit Systems - meteric • Metric Prefixes, see page 9

  21. Unit Systems • Using prefixes • Base unit = meter • Kilometer = km = _________ m

  22. Unit Systems • International System (SI) • Adopted in 1960 • Internationally agreed upon set of units • Used in industry and science • See page 9

  23. What chemists measure • Length – distance between 2 points • Metric base = _____________ • Mass – quantity of matter present • Base unit: __________ • Weight – measure of gravitational pull on an object • Base unit: ___________

  24. Mass and Weight • Measure mass on a balance. • Measure weight on a scale.

  25. Volume • Volume – amount of three dimensional space occupied by an object • SI base = meter3 • Metric base = Liter = dm3 • dm = ______ cm • dm3 = ___________ cm3 • Equivalent units: • mL = _______ = ________

  26. Uncertainty in Measurement (1.3) • All measurements include some degree of uncertainty • A properly taken measurement includes all of the certain digits and one uncertain (estimated) digit

  27. Taking measurements • When taking a measurement you record: • All known digits • those marked on the measuring device • One estimated digit • A multiple of 1/10 the smallest marked unit on the measuring device

  28. Taking measurements • Thermometer example • Graduated cylinder example

  29. Accuracy and Precision • Accuracy – how close a measured value agrees with the true value • Ideally values will differ in only the estimated digit

  30. Accuracy and Precision • Precision – how closely repeated measurements agree with each other • Ideally the values will differ in only the estimated digit

  31. Evaluating a measuring device • Good measuring devices are both accurate and precise • Readings taken with a precise, but not accurate measuring device can be corrected.

  32. Types of Errors • Random error • Value has an equal probability of being high or low • Compensate for random errors by: • Systematic error • Value recorded is consistently low or high • Compensate for systematic errors by:

  33. Significant Figures and Calculations (1.5) • A measurement includes all the certain digits and one estimated (uncertain) digit • These digits are called the significant figures of a measurement. • All calculations based on measurements must reflect the uncertainty of the original measurements.

  34. Significant Figures • Rules for counting significant figures • Rules for rounding off calculations based on significant figures

  35. Counting Significant Figures • All nonzero integers are significant. • 35.76 g = _______ sig. fig.

  36. Counting Significant Figures • Zeros • Leading zeros are NEVER significant • 0.0037 mL = _____ sig fig • Captive zeros are ALWAYS significant • 7.098 g = ______ sig. fig.

  37. Counting Significant Figures • Zeros • Trailing zeros are significant only if the value includes a decimal place. • 3570 g = ______ sig. fig. • 7.500 kg = ______ sig. fig.

  38. Counting Significant Figures • Exact Numbers have unlimited significant figures • Numbers obtained by counting • 23 students • Definitions • 1 foot = 12 inches • 1 inch = 2.54 cm (exactly)

  39. Rules for Rounding Off • If the first digit to be removed is: • Less than 5, the preceding digit remains the same • 5 or greater, the preceding digit is increased by 1

  40. Significant Figures and Calculations • Multiplication and Division • The answer is rounded to the same number of sig. fig. as the measurement with the fewest sig. fig. (3.50 x 102 mL) x 0.7030 g/mL =

  41. Significant Figures and Calculations • Addition and Subtraction • The answer is rounded to the same number of decimal places as the measurement with the fewestdecimal places. 32.05 g + 5.3978 g + 6.30 g =

  42. Dimensional Analysis (1.6) • Convert the number of minutes left in class to seconds. • Open to Appendix A26 • PRACTICE!

  43. Dimensional Analysis • The largest pumpkin at last year’s Windsor fair weighed 673 pounds. • Express the mass of this pumpkin in grams and in kg.

  44. Dimensional Analysis • A block of wood has a volume of 2.50 ft3. • Express the volume of the wood block in cm3.

  45. Dimensional Analysis • The world's oceans have a surface area of 361,100,000 square kilometers. • Express this surface area in square miles. Please put your final answer in scientific notation.

  46. Dimensional Analysis • Water has a density of .998 g/mL at room temperature. • Express the density of water in pounds/gallon. • Game plan?

  47. Temperature (1.7) • Temperature Scales (units) • Fahrenheit (0F) • Used in this country • Celsius (0C) • Used in the physical science • Kelvin (K) • SI unit for temperature • Used in gas law calculations

  48. Temperature

  49. Temperature

  50. Temperature Conversions TK = TC + 273.15 TC = (TF - 32) 1.8 TF = (1.8) TC + 32

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