Measurement and Significant Figures

1. Measurement andSignificant Figures www.lab-initio.com

2. How to survive and thrive AP ChemIsTRY • Steps to survive & thrive in AP Chem! • 1 Review all of your old notes from chemistry class. If you don't have those, ask somebody who has taken neat notes from a prior class and study those. The main point here is to simply refresh your memory: you're not going to remember it all or even be close. • 2 Walk into AP Chemistry with some confidence and swagger. Don't be intimidated: do it to it. • 3 Take notes and make flashcards of ideas and formulas. Try to synthesize your own flashcards and not just copy from the book and your notes. • 4 Read the chapter at least three times before the test. Sounds like overkill, but it's not. • "How should you study? Study like there's going to be an exam on the material the next morning. If you study like that, you won't have to worry about cramming for the exam later." - Unknown professor.

3. How to survive and thrive AP ChemIsTRY • 5 Keep in mind your fundamental properties of everything chemistry related. Start with the basic states of matter and end with the chemical properties such as pH and electronegativity. Cover the bases. • 6 Don't be afraid of pH. It's a pain in the butt, yes. Will it hurt you to do outside practice problems from the internet? Of course not. • 7 Use the internet often for extra practice. There are countless resources out there on the internet, and the problems are all different. Meaning: you won't get a narrow mental work out. • 8 Watch your stoichiometry. A lot of problems will be set up perfectly within the problem itself, keep your eyes peeled. • 9 Memorize your strong acids and bases. They ionize 100%, and are therefore pretty darn important. • 10 It's okay if you don't get it right the first time.

4. How to survive and thrive AP ChemIsTRY • 11 Try again and again. Until you get it perfect. • 12 Work through old tests and practice tests on the internet. It could be the difference between passing and failing the exam. • 13 Make mnemonic devices for everything. It especially helps with cations and anions. • 14 Do ALL of your homework assignments. Some teachers look simply for effort. • 15 Practice makes perfect test scores. By doing problems related to your current material, you can be fully readied for that material's test or quiz.

5. UNIT 0 REVIEW • Purchase 5 steps to a 5 • 2013-2014 edition (NOT OLD) • Review • VERY FAST – look at your notes, find where you were weak and START STUDYING • Review thru pg 11 in class, rest on your own • Help as needed • Use old notes • Use links on website!! Lots of help online!

6. Scientific problem solving • 1. Observations • - quantitative (involve #’s or measurement) • - qualitative ( don’t invole #’s) • 2. Formulating hypothesis • - possible explanation for the observation • 3. Performing experiments • - gathering new information to decide whether the hypothesis is valid - Results and observations lead to modifying the hypothesis

7. Theories become laws • Eventually, after many experiments the hypothesis may graduate to become a theory • A theory gives a universally accepted explanation of the problem • A theory gives a universally accepted explanation of the problem. • Theories should be constantly challenged and refined with new data and evidence.

8. Theories become laws • Theories are different from laws. • Laws state the general behavior that occurs naturally in nature. • Ex: Law of conservation of Mass is a law because we have observed over and over that mass is not created or destroyed but only changes form.

9. Law vs. Theory A law summarizes what happens A theory (model) is an attempt to explain why it happens. Einstein's theory of gravity describes gravitational forces in terms of the curvature of spacetime caused by the presence of mass

10. Extensive vs. Intensive Properties • Intensive properties do not change with amount of substance; are used for identification • a. Examples: density, melting point, boiling point, color, conductivity • Extensive Property--depends on the amount of matter present • b. These properties CANNOT be used to ID the substance!! • a. ex: mass, volume, length …..

12. Physical vs. Chemical Properties • Physical Property--can be observed without changing the identity of the substance • melting point- temp it changes from solid to liquid • ductility- able to be pulled into a thin wire • Viscosity- how quickly or slowly a fluid flows • solubility- will it dissolve in water

13. 2. Chemical Property--These characteristics are observed ONLY when a substance changes into a different substance • a. examples of Chemical Properties • 1) Combustible/flammable: able to burn • a) Examples & Facts: all chemicals come with a label that identifies their level of flammability • --oxygen & hydrogen are very flammable gases • --carbon dioxide is not a very flammable gas

14. C. Physical vs. Chemical Changes • Physical Changes--change the form of a substance without changing its identity; properties remain the same • Often reversible • Change of state most common

15. What are the Phase Changes?

17. Chemical Changes--change the identity of a substance; products have new & different properties • Usually NOT reversible • Signs of a Chemical Change • a. change in color or odor • b. formation of a gas • c. formation of a precipitate formed (a precipitate is a solid product which forms in a chemical reaction)

18. 4. Chemical Change examples • a. corrosion: slow reaction & wearing away of metals (rusting, tarnishing) • b. rusting- iron reacting with oxygen • c. burning a log

19. Elements, mixtures and compounds • An element is defined as a substance that cannot be broken down into other substances by chemical means. The elements are listed on the periodic table. • A compound is formed when a number of these elements bond together. Compounds always have a fixed composition, i.e. they always contain the same definite amount of each element present in the compound; • for example, a water molecule always contains two hydrogen atoms bonded to an oxygen atom and has the formula H2O. If that composition is altered, the chemical formula changes and the substance ceases to be water

20. Platinum • A mixture has varying composition and is made up of a number of pure substances. Mixtures can be; • (i) Homogeneous. Uniform in composition throughout a given sample but the composition and properties may vary from one sample to another; for example a solution of salt water, • (ii) Heterogeneous. Have separate, distinct regions within the sample. As a result the composition and properties vary from one part of the mixture to another; for example a chocolate chip cookie. • All pure substances are either elements or compounds.

22. Separation of mixtures • Separation of Mixtures • Filtration – solid substances are separated from liquids and solutions. • Distillation – uses differences in the boiling points of substances to separate a homogeneous mixture into its components. • Chromatography – separates substances on the basis of differences in solubility in a solvent.

23. Nature of Measurement A measurement is a quantitative observation consisting of 2 parts: • Part 1 - number • Part 2 - scale (unit) • Examples: • 20 grams • 6.63 x 10-34Joule·seconds

24. Celsius & Kelvin

25. SI Prefixes Common to Chemistry

26. Rules for Counting Significant Figures - Details • Nonzero integersalways count as significant figures. • 3456has • 4 sig figs.

27. Rules for Counting Significant Figures - Details • Zeros • - Leading zeros do not count as significant figures. • 0.0486has • 3sig figs.

28. Rules for Counting Significant Figures - Details • Zeros • - Captive zerosalways count as significant figures. • 16.07has • 4sig figs.

29. Rules for Counting Significant Figures - Details • Zeros • Trailing zeros are significant only if the number contains a decimal point. • 9.300has • 4sig figs.

30. Rules for Counting Significant Figures - Details • Exact numbershave an infinite number of significant figures. • 1inch=2.54cm, exactly

31. Sig Fig Practice #1 How many significant figures in each of the following? 1.0070 m  5 sig figs 17.10 kg  4 sig figs 100,890 L  5 sig figs 3.29 x 103 s  3 sig figs 0.0054 cm  2 sig figs 3,200,000  2 sig figs

32. Rules for Significant Figures in Mathematical Operations • Multiplication and Division: • # sig figs in the result equals the number in the least precise measurement used in the calculation. • 6.38 x 2.0 = • 12.76 13 (2 sig figs)

33. Sig Fig Practice #2 Calculation Calculator says: Answer 22.68 m2 3.24 m x 7.0 m 23 m2 100.0 g ÷ 23.7 cm3 4.22 g/cm3 4.219409283 g/cm3 0.02 cm x 2.371 cm 0.05 cm2 0.04742 cm2 710 m ÷ 3.0 s 236.6666667 m/s 240 m/s 5870 lb·ft 1818.2 lb x 3.23 ft 5872.786 lb·ft 2.9561 g/mL 2.96 g/mL 1.030 g ÷ 2.87 mL

34. Rules for Significant Figures in Mathematical Operations • Addition and Subtraction: The number of decimal places in the result equals the number of decimal places in the least precise measurement. • 6.8 + 11.934 = • 18.734  18.7(3 sig figs)

35. Sig Fig Practice #3 Calculation Calculator says: Answer 10.24 m 3.24 m + 7.0 m 10.2 m 100.0 g - 23.73 g 76.3 g 76.27 g 0.02 cm + 2.371 cm 2.39 cm 2.391 cm 713.1 L - 3.872 L 709.228 L 709.2 L 1821.6 lb 1818.2 lb + 3.37 lb 1821.57 lb 0.160 mL 0.16 mL 2.030 mL - 1.870 mL

36. Uncertainty in Measurement • A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty. • Measurements are performed with instruments • No instrument can read to an infinite number of decimal places

37. Precision and Accuracy • Accuracy refers to the agreement of a particular value with the true value. • Precision refers to the degree of agreement among several measurements made in the same manner. Precise but not accurate Precise AND accurate Neither accurate nor precise

38. Accuracy & Precision • Consider 3 sets of data that have been recorded after measuring a piece of wood that is exactly 6.000 m long. • Which set of data is the most accurate? • Set Y • Which set of data is the most precise? • Set Y

39. Review on your own… • Review the notes on atomic theory and know the major points, Dalton’s atomic theory, and the chart on experiments • Review calculations of P, N, E, atomic number, mass number and ions. • Review periodic table structure, know metals, non-metals and metalloids (semi) • Review ALL nomenclature, polyatomic ions, ionic compounds, covalent compounds, acids, oxoanions & oxoacids (we did oxoacids, we just didn’t label them as such) • Don’t forget stock system, hydrates, etc.