Chemistry I

1. Chemistry I Introduction, Review of Required Prerequisites, & Lab Safety

2. What is Chemistry? • Chemistry is the study of matter and the changes that it undergoes • A basic understanding of chemistry is central to all sciences: biology, physics, Earth science, ecology, etc. • Branches of chemistry include: • Organic Chemistry • Inorganic Chemistry • Physical Chemistry • Analytical Chemistry • Biochemistry • Who cares! How much can I get paid for learning this stuff? • More than a teacher!!! • Scientific Research – Chemist, Chemical Engineer, Consultant, Forensics, Food and Flavor Chemist, Geochemist, Medicine or even business/finance • About 40-60k for starting pay with B.S. and M.S. and 100k-200k for medical field

3. Chemistry = Conversions = Math = Problems • So go and buy a good calculator and stop stealing them from my desk!!! • SI Units – Metric System

4. Scientific Method • Do you know the steps to the scientific method? • In order and completely? • Do you know the process of publishing, peer review, creating a theory? • The difference between a theory and a scientific law?

5. The Scientific Method : Observe Question Hypothesize Test hypothesis by observations and/or experimentation Collect data Draw a conclusion Modify hypothesis if necessary Test again … Experiments must be able to be repeated by others. Science is loosely described as the search for knowledge. It is “observation, study, and experimentation to find out about the nature of things.” Social or Natural including: Psychology Biology Sociology Physical … Earth… The Nature of Science

6. Observations • Gathered through your senses • A scientist notices something in their natural world

7. Observations • An exampleof an observation might be noticing that many salamanders near a pond have curved, not straight, tails

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

9. Hypothesis • An example of a hypothesis might be that the salamanders have curved tails due to a pollutant in the moist soil where they live.

10. Experiment • A procedure to test the hypothesis.

11. Experiment A good or “valid” experiment will only have ONE variable!

12. Experiment Variable – factor in the experiment that is being tested

13. Controls and Variables

14. Scientific Experiments Follow Rules • An experimenter changes one factor andobserves or measureswhat happens.

15. The Control Variable • The experimenter makes a special effort to keep other factors constant so that they will not affect the outcome. • Those factors are called control variables.

16. What is the Purpose of a Control? • Controls are NOT being tested • Controls are used for COMPARISON

17. Other Variables • The factor that is changed is known as the independent variable. • The factor that is measured or observed is called the dependent variable.

18. Example of Controls & Variables • For example, suppose you want to figure out the fastest route to walk home from school. • You will try several different routes and time how long it takes you to get home by each one. • Since you are only interested in finding a route that is fastest for you, you will do the walking yourself.

19. What are the Variables in Your Experiment? • Varying the route is the independent variable • The time it takes is the dependent variable • Keeping the same walker throughout makes the walker a control variable.

20. One more thing… it is best to make several trials with each independent variable.

21. Valid Experiments

22. Remember: To be a Valid Experiment: • Two groups are required --- the control & experimental groups • There should be only onevariable

23. Data • Results of the experiment • There are two ways to describe or analyze your data: • Qualitative Data– Tells about qualities of an object or thing. • Smell, color, sound, etc. • Think QUALITative, Quality. • Quantitative Data– Tells about quantity, or numbers of data. • 5 inches, 10 lbs, 12 minutes, etc. • Think QUANTITative, Quantity.

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

25. Data • When analyzing data, you have to account for error in your work. • Error is an expression of the amount of imprecision in a set of measurements. • Error is commonly expressed as percentage error. • Example: Today, there is a 45% chance of rain, +/- 2%.

26. *Organizing Data Line Graphs Pie Charts Bar Graphs Continuous Change Comparison of similar things X-Axis = independent Happens anyway, like time Y-Axis = dependent it is a result of the test parts/portions/percents of a whole

27. Which is Which???

28. Graphing • The independent variable (the factor that is changed during an experiment) is always on the X-axis • The dependent variable (the factor that is being measured during an experiment) is always on the Y-axis • Best Fit Line – Questions on this? • (0,0) is not always the best starting point for best fit lines, if the origin is not a valid data point • PLEASE LABEL YOUR GRAPHS AND TABLES • Titles, Axes Labels, Units, etc.

29. Algebra and Graphs • Anyone know the equation for a linear relationship between two points? • Slope? • Challenge: • If the data collected did not give a straight best-fit line, and it happened to be parabolic, what is the equation for a quadratic relationship? y = ax2 + bx+ c

30. Conclusion • The answer to the hypothesis based on the data obtained from the experiment

31. Retest In order to verify the results, experiments must be retested.

32. Acceptance of Scientific Ideas • After you analyze results, next you have to publicize them. • There is a system of review all scientists follow to check their work, and it is called peer review. • Peer review is when many different scientists review your work and either approve, or disapprove it. • Approved work is published and made available to the public. • Unapproved work is not published at all.

33. Acceptance of Scientific Ideas • After results have been published, they are usually replicated many times. • When a hypothesis has been tested over and over and is generally accepted by scientists, it becomes a theory. • Theories are based on scientific laws. A law is an explanation of the natural world that has no exceptions. • Example: • The Big Bang Theory • Theory of Gravitation • etc.

34. Sciences are integrated,so it is important to know something of each. • Technology = science put to work/use. • Scientific theory = an explanation that has been tested by repeated observation; simple explanation of observations that leads to further predictions. • Scientific law = observation of nature without explanation. Example: Law of gravity. • Data may be qualitative (descriptive words), or quantitative (numbers). • Data may lead to a change, or update, in a theory. • Example: Caloric theory → Kinetic theory • Models (computer, physical, illustrated…) may be used to aide in predictions, and to represent reality.

35. The Way Science Works… • Be sure to test only one variable at a time. • Remember that no experiment is a failure because it still brings about more data/observations. • Tools of science include the fancy specialized tools, as well as the logic of critical thinking, and the basic physical observation.

36. Solving a Problem 1) Identify a Problem 2) State Observations about the problem 3) Form a Hypothesis about the problem (if…then…) 4) Design an Experiment to test the hypothesis 5) Collect Data 6) Form a Conclusion 7) Retest

37. Measurements • Precision vs. Accuracy • Precision is the degree of exactness of a measurement • Accuracy is how well the results of a measurement agree with the “real” value; that is the accepted value as measured by a competent experimenters. • Therefore, (quick summary) • use equipment correctly • make all readings at eye level • don‘t “guesstimate” a value • ask for help

38. Reporting Measurements • Using significant figures • Report what is known with certainty • Add ONE digit of uncertainty (estimation)

39. Math Review • Conversions • Anyone need to review, speak now? • Dimensional Analysis? • Significant Digits • Must Use These!!

40. Significant Figures • The valid digits in a measurement are called significant digits • The last digit given for any measurement is the uncertain digit • All nonzero digits in a measurement ARE significant • Rules for counting significant figures are summarized below. • Zeros within a number are always significant • e.g. Both 4,308 and 40.05 contain four significant figures • Zeros that do nothing but set the decimal point MAYBE significant • e.g. Thus, 470,000 has two significant figures (or 3, 4, 5, or even 6!!!) • Trailing zeros that aren't needed to hold the decimal point are significant • e.g. 4.00 has three significant figures

41. 46 1.9858e-3 .00746 21.0 .05343 1479. 2518.00 .049 392 .002241 1.67e-2 2 5 3 3 4 4 6 2 3 4 3 Sig. Figs.

42. Sig. Figs. • 1200 • 1200. • 120.0 • 2.9813 x 10-12 • 0.004 • .004 • 0.0043 • 0.00430 • 123456789 • 2 (maybe 3 or 4) • 4 • 4 • 5 • 1 • 1 • 2 • 3 • 9

43. Significant Figures • If you are not sure whether a digit is significant, assume that it isn't • For example, if the directions for an experiment read: "Add the sample to 400 mL of water," assume the volume of water is known to one significant figure • Exact numbers are known with complete certainty • Try this one: 5,280 feet in a mile… how many significant figures? • In addition and subtraction, the result is rounded off to the last common digit occurring furthest to the right in all components • In other words, the result is rounded off so that it has the same number of decimal places as the measurement having the fewest decimal places • For example: 104.630 + 27.08362 + 0.61 = 132.32362 • This should be rounded to 132.32 (2 decimal places)

44. Significant Figures • In multiplication and division, the result should be rounded off so as to have the same number of significant figures as in the component with the least number of significant figures • For example: 3.0 (2 sig figs ) × 12.60 (4 sig figs) = 37.8000 • Round it off to 38 (2 significant figures) “The answer in a calculation cannot be more precise than the values in the calculation.”

45. How many decimal places are needed? How many sig. figs. in the answer? • 4.389 + 812.1233 + 128.1 = • 1 • 1.1234 – 12.5223 + 9.998 = • 3 • 871.12598 + 1238.71238 = • 5 • 11235 * 1234 * 87 = • 2 • 49837 ÷ 34.23491 = • 5 • 0.00691 * 4.001 * 580001 = • 3 Sig. Figs. Continued

46. Chemical Properties Chemical properties describe how a substance reacts. Some elements are very reactive and occur in nature combined with other elements. Other elements are non-reactive, such as gold. A chemical reaction or change results in the production of: new substance new color odor or gas precipitate change in energy Physical Properties Physical properties can be observed without a chemical change/new product. Size, shape, texture may change, but it is still the same stuff. Dissolving is a physical change. Physical properties include color, size, shape, density, taste, smell, feel, sound, texture, melting point, boiling point, strength, hardness, solubility, conductivity,… What are the states of matter? Properties of Matter

47. Physical Property - Density • Density: The ratio of Mass to Volume • Density = Mass / Volume (D = M/V) • Mass is the amount of material that makes a substance • Volume is the amount of space the object physically occupies in a three-dimensional space • Besides measuring length, width, & height, what is another method of measuring volume? • Since density is a physical property, it can be used to identify substances

48. Chemical Property • A chemical property is one that describes how a substance reactions and thus subsequently changes into something else • These are also known as Chemical Reactions mercury (II) oxide  mercury + oxygen Reactants Products

49. Physical and Chemical Properties Examples of Physical Properties Boiling point Color Slipperiness Electrical conductivity Melting point Taste Odor Dissolves in water Shininess (luster) Softness Ductility (form wire) Viscosity (resistance to flow) Volatility (vapor)Hardness Malleability Density (mass / volume ratio) Examples of Chemical Properties Burns in air Reacts with certain acids Decomposes when heated Explodes Reacts with certain metals Reacts with certain nonmetals Tarnishes Reacts with water Is toxic Chemical properties can ONLY be observed during a chemical reaction!

50. Intrinsic Extrinsic • Characteristics or properties of matter that DO NOT depend on the amount of matter present • These characteristics do not change with changing amounts of matter • These can be used to find the identify of an unknown sample • Phase, color, taste, texture, density, solubility, melting/boiling point, etc. • Characteristics or properties of matter that DO depend on the amount of matter • These properties change with changing quantities • Mass, volume, weight, etc. Intrinsic vs Extrinsic Properties