study of substances and changes between them

1. study of substances and changes between them

2. Balloon filled w/hydrogen gas. (chemistry requires all 3 ways of thinking) • Should we consider: • Whole balloon? Macroscopic • Gas molecules flying/bouncing inside? Molecular-level • Should you write formulas/equations? Symbolic

3. Macroscopically-think about things large enough to see, feel, weigh, etc. • Molecular-level-focus on molecules and how they behave: • If match held to balloon and it explodes, you see how they collide and react with other molecules. http://college.hmco.com/chemistry/shared/media/animations/oxygenhydrogensoapbubblesb.html http://wps.aw.com/bc_suchocki_chemistry_se/0,6823,526240-nav_and_content,00.html

4. What is an explosion? • Chemical level-reaction that releases a lot of energy fast (creating flash and boom). • Light hydrogen balloon-hydrogen reacts w/oxygen in air. • Before reaction, we had hydrogen in balloon and oxygen in air. • During explosion, H/O transformed to new substance - water. • Substances that enter into reaction-reactants. • New substance(s) produced by reaction-products.

5. What made the balloon explode? 2H2 + O2 2H2O Symbolic expressions common: H2 = hydrogen gas in balloon Chemical substance has name and formula (more convenient). Symbolic-chemical equation stands for what happens when hydrogen and oxygen meet over a flame

6. Can be read like a sentence. • Chemical formulas stand for names of reactants and products. • Plus sign (+) means "and" or "reacts with" (or words to that effect). • Arrow means "to produce" (or words to that effect). • H2 + Cl2 2HCl • Hydrogen reacts with chlorine to produce hydrochloric acid. • Or: Hydrochloric acid is produced from the reaction of hydrogen and chlorine.

7. Basic VS. Applied Research

8. Basic (fundamental/pure) research:curiosity or interest in scientific questionexpand knowledge, not create or invent something • No obvious commercial value to resulting discoveries: • How did the universe begin? • What are protons, neutrons, electrons composed of? • How do slime molds reproduce? • What is the specific genetic code of the fruit fly?

9. Applied research:designed to solve practical problems of modern world, rather than to acquire knowledge for knowledge's sake. • Goal of applied scientist is to improve the human condition: • Improve agricultural crop production. • Treat or cure a specific disease. • Improve energy efficiency of homes, offices, or modes of transportation.

10. Distinction between basic and applied research isn't always clear. • It sometimes depends on your perspective or point of view. • How long will it be before some practical application results from the research? • If a practical use is only a few years away, then the work can be defined as strictly applied research. • If a practical use is still 20-50 years away, then work is somewhat applied and somewhat basic in nature. • If practical use cannot be envisioned in foreseeable future, then work described as purely basic research.

11. There has been a noticeable shift in philosophyregarding the types of research receiving federal funding in recent years. • Universities get much of their money from the National Science Foundation (NSF). • Research at the Berkeley National Laboratory is funded primarily by the Department of Energy (DOE) and the National Institutes of Health (NIH). • Congress-strong influence on what types of research get funded-it allocates money to these various federal agencies. • Some members of Congress want to see less money given to basic research projects that probably will not lead to applied work for quite some time. • Shift in national priorities greatly concerns scientists.

12. Industry does little basic research today (expensive) • Very competitive-commercial research emphasizes projects requiring <10 years to develop a new product or process. • So universities and government laboratories left with the responsibility to carry out basic research and long-term applied research.

13. Extract general principles from observed facts by using scientific method

15. Observation (things perceived or measured directly) • Start w/observed facts about substances and processes: • Must be reliable-our senses should perceive what is real without any distortion or illusion. • Must be objective-should accept what we see, not what we wish to see. • Often extend senses w/measuring instruments-observe things that can't be observed w/unaided senses. • Should be as precise as possible-measurements of same thing should always give nearly same result.

16. Hypothesis (“educated guess”) • Observations  general principle that explains all facts (hypothesis): • Must be inclusive-it explains all the observed facts. • Must be useful-it leads to predictions about other related situations. • Must be testable-set up conditions of any prediction to see if prediction is true.

18. Experiment • Hypothesis  test it w/experiment. • Hypothesis must generate prediction in form, “if/then” • "If hypothesis is true & some conditions A exist, then B must be true." • A-set of conditions, B-predicted outcome. • During experiment, generate conditions A, see if B results: • If it does, hypothesis passed test. • If conditions A do not lead to result B, then we must conclude that there is something wrong in hypothesis.

19. Must be reproducible: Since errors can be made, it is necessary to repeat experiment to see if it always give same results. Doesn't-may be variable changing/affecting outcome: Must determine variable and control it before deciding validity of original hypothesis. Before accepting hypothesis, other workers, preferably in other labs, must reproduce same results.

20. If a hypothesis fails an experimental test, it will be necessary to go back one step and come up with a new hypothesis: Obtains new observation to add to original set. However if now hypothesis does not predict results of this experiment, it is no longer inclusive. Replace hypothesis with completely new one or modify it so it explains original observation and new one also. New hypothesis must then be tested further.

22. Theories or Laws • Once hypothesis has been tested numerous times, by many people, for all possible predictions, then confidence in that explanation will be high-hypothesis starts to be called theory • "law" often used interchangeably w/"theory". • However a law is more properly a theory that carries a very high level of confidence in its truth. • Law explains very broad range of observations and/or being consistent with common sense experience.

23. Laws describe some fundamental characteristic of the universe while a theory may give an explanation of phenomena in terms that are not directly observable: Newton's Laws of Motion can easily be observed by anyone in the motion of everyday objects. Theory of gravitation is intended to explain why gravity exists, why it has certain observable characteristics.

24. Hypothesis vs. theory: Hypothesis: Untested supposition. May or may not be valid. Theory: Carries a high level of confidence that it is true. Exists as statement of general principles of our present understanding of what is/isn't true.

25. A limitation of scientific method-theory is only as good as next test • Only justification for rejecting theory-observation is made that contradicts theory or one of its predictions. • Is always possible and has happened numerous times: • Newton's Laws of Motion almost certainly true but theory of gravitation invalid-doesn't completely explain Mercury’s orbit. • This inspired Einstein to formulate a completely new explanation of gravity in his theory of relativity. • Newton's theory still used for most celestial mechanics since it works fine in most cases. • Only in regions of high gravity does it give wrong answers. • Example where important/useful theory is retained within limits though we know it is invalid outside those limits. • Is it untrue? Perhaps, but still useful if we know how to use it

27. 3 primary areas for which science can't help us answer our questions Same problem: questions they present don't have testable answers. Since testability is so vital to scientific process, these questions simply fall outside venue of science.

28. Science can't answer questions about value: "Which of these flowers is prettier?" or “Which smells worse, a skunk or a skunk cabbage?" "Which is more valuable, 1 ounce of gold or 1 ounce of steel?" Gold is valuable, but would you build skyscraper with gold?-which has more value?

29. Science can't answer questions of morality: Problem of deciding good and bad, right and wrong, is outside determination of science.

30. Science can't help us with questions about supernatural: Prefix means "above"-"above (or beyond) the natural“. Scientist use only natural laws of universe.

31. Beginning of any scientific study is gathering of observations. • Observations must be reliable and objective. • Observations often involved the making of measurements which result in quantity with certain magnitude and some units (153 cm). • Always involves some error or uncertainty.

32. Accuracy vs. Precision • Accuracy-difference between measured value and “true” value (telling truth). • Precision-indication of how close multiple measurements would be expected to agree. (telling same story over and over again).

33. Accuracy and precision are then two different things: accuracy = truth = bull’s eye (is it close to the accepted value?) precision = closeness of all darts

34. Any quantity that is the result of a measurement has a built-in error. • Error and uncertainty is due to limitations of any measurement process. • Error may be systematic, always in same direction, or random, scattered around a central value.

35. There are two major ways to determine the precision of a measurement. • 1st depends on precision of measuring instrument. • Suppose one is measuring the length of a tabletop. • Use a ruler marked in cm.-length between 153 and 154 cm

36. You cannot say what fraction of a cm beyond 153 cm it is since there are no markings for fractions of a cm. Since edge seems closest to 153-report length as 153 cm. If length anywhere from halfway between 154 and 153 to halfway between 153 and 152-still report it as 153 cm. That is, the length would be 153 cm ± 0.5 cm. The error margin is thus a total of 1 cm wide. We say the length was 153 cm to the nearest cm. Since smallest division was 1 cm-ruler has precision of 1 cm. Any measurement w/this will have precision to nearest cm. Use ruler with divisions of 0.1 cm: between 153.0 and 153.1 cm

37. Length is 153.0 cm to the nearest 0.1 cm. Precision is 0.1 cm. Measurements more precise though length of table has not changed, only the instrument used has changed. Added a decimal place in number even though digit was 0 Measurements reported so that last digit contains the error. Digit called uncertain digit. When you see # representing a measured quantity, you understand that precision is to within the last decimal place.

38. 2nd way involves procedures producing multiple measurements Suppose you have balance that can be read to nearest cg. Assume precision of mass would be within 1 cg Four weighing of an object gave you the following data: Weighing Mass 1 24.56 2 24.62 3 24.58 4 24.64

39. The mean value (average) is 24.60 g. However-obvious that random error > 0.01 g. Values vary so much that 1st decimal place is uncertain Should it be 24.6 or 24.5? Report value only to first decimal place, as 24.6 g. Balance is only precise to within 0.1 g. Measurement s/b rounded off to single largest uncertain digit Quantity has # significant figures-smallest contains error Any measured quantity should always be rounded to correct # significant figures to show precision Thus uncertainty in quantity 3.45 g is 0.01 g; the uncertainty in 34.5 mL is 0.1 mL; the uncertainty in 23 L is 1 L.

40. Homework: Read 1.1-1.2, pp. 1-10 Q pp. 31-32, #2, 7-10 Q pg. 34, #7, 8, 10

41. Significant Figures:

42. Result of measurement s/b rounded so lowest digit contains error • Even if you have more digits, discard the extra. • If the last nonzero digit is larger than the error add zeros. • Digital scale reads mass of an object as 1.344 g but you know it is only precise to 0.1 g. • Round to the tenth's digit and report it as 1.3 g. • Length is 1 m long, but meter stick marked to nearest mm. • Report it as 1.000 m-to the nearest 0.001 m = 1 mm.

43. Significant Figures: last significant figure indicates precision • All nonzero digits are significant. • e.g. 2300 has only two SF, 2 and 3. • Zeros between significant figures are significant. • e. g. 105 has three SF. • Trailing zeros in # with a decimal point are significant. • e. g. 1.00 and 100. both have three SF. • Trailing zeros in # with no decimal point are not significant. • e. g. 200 and 300 both have only 1 SF. • Leading zeros are never significant. • e. g. 0.12 has two SF.

47. Give the correct number of significant figures for 4500, 4500., 0.0032, 0.04050 • 2, 4, 2, 4 • Give the answer to the correct number of significant figures: 4503 + 34.90 + 550 = ? • 5090 (3 significant figures - round to the tens place - set by 550) • Give the answer to the correct number of significant figures: 1.367 - 1.34 = ? • 0.027 (1 significant figure - round to hundredths place) • Give the answer to the correct number of significant figures: (1.3 x 103)(5.724 x 104) = ? • 7.4 x 107 (2 significant figures - set by 1.3 x 103) • Give the answer to the correct number of significant figures: (6305)/(0.010) = ? • 6.3 x 105 (2 significant figures - set by 0.010)

48.  37.76 + 3.907 + 226.4 =  •  319.15 - 32.614 =  •  104.630 + 27.08362 + 0.61 =  •  125 - 0.23 + 4.109 =  •  2.02 × 2.5 =  •  600.0 / 5.2302 =  •  0.0032 × 273 =  •  (5.5)3 =  •  0.556 × (40 - 32.5) =  •   45 × 3.00 =  •   3.00 x 105 - 1.5 x 102 = (Give the exact numerical result, then express it the correct number of significant figures). •   What is the average of 0.1707, 0.1713, 0.1720, 0.1704, and 0.1715?

49.  37.76 + 3.907 + 226.4 = 268.1 •  319.15 - 32.614 = 286.54 •  104.630 + 27.08362 + 0.61 = 132.32 •  125 - 0.23 + 4.109 = 129 •  2.02 × 2.5 = 5.0 •  600.0 / 5.2302 = 114.7 •  0.0032 × 273 = 0.87 •  (5.5)3 = 1.7 x 102 •  0.556 × (40 - 32.5) = 4 •  45 × 3.00 = 1.4 x 102 •  3.00 x 105 - 1.5 x 102 = (Give the exact numerical result, then express it the correct number of significant figures). • What is the average of 0.1707, 0.1713, 0.1720, 0.1704, and 0.1715? Answer = 0.1712

50. Homework: