2 Steps in the Scientific Method 1. Observations- quantitative- qualitative2. Formulating hypotheses- possible explanation for the observation3. Performing experiments- gathering new information to decidewhether the hypothesis is valid
3 Outcomes Over the Long-Term Theory (Model)- A set of tested hypotheses that give an overall explanation of some natural phenomenon.Natural Law- The same observation applies to many different systems
4 A law summarizes what happens Law vs. TheoryA law summarizes what happensA 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
5 Nature of Measurement Part 2 - scale (unit) A measurement is a quantitative observation consisting of 2 parts:Part 1 - numberPart 2 - scale (unit)Examples:20 grams6.63 x Joule·seconds
6 The Fundamental SI Units (le Système International, SI)
9 SI Prefixes Common to Chemistry Unit Abbr.ExponentMegaM106Kilok103Decid10-1Centic10-2Millim10-3Micro10-6Nanon10-9Picop10-12
10 Uncertainty in Measurement A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.Measurements are performed withinstrumentsNo instrument can read to an infinite number of decimal places
11 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.Neither accurate nor precisePrecise but not accuratePrecise AND accurate
12 Types of ErrorRandom Error (Indeterminate Error) - measurement has an equal probability of being high or low.Systematic Error (Determinate Error) - Occurs in the same direction each time (high or low), often resulting from poor technique or incorrect calibration. This can result in measurements that are precise, but not accurate.
13 Rules for Counting Significant Figures - Details Nonzero integers always count as significant figures.3456 has4 sig figs.
14 Rules for Counting Significant Figures - Details Zeros- Leading zeros do not count as significant figures.has3 sig figs.
15 Rules for Counting Significant Figures - Details Zeros- Captive zeros always count as significant figures.16.07 has4 sig figs.
16 Rules for Counting Significant Figures - Details ZerosTrailing zeros are significant only if the number contains a decimal point.9.300 has4 sig figs.
17 Rules for Counting Significant Figures - Details Exact numbers have an infinite number of significant figures.1 inch = cm, exactly
18 Sig Fig Practice #1 1.0070 m 5 sig figs 17.10 kg 4 sig figs How many significant figures in each of the following?m 5 sig figs17.10 kg 4 sig figs100,890 L 5 sig figs3.29 x 103 s 3 sig figscm 2 sig figs3,200,000 2 sig figs
19 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)
20 Sig Fig Practice #2 Calculation Calculator says: Answer 3.24 m x 7.0 m 100.0 g ÷ 23.7 cm3g/cm34.22 g/cm30.02 cm x cmcm20.05 cm2710 m ÷ 3.0 sm/s240 m/slb x 3.23 ftlb·ft5870 lb·ft1.030 g ÷ 2.87 mLg/mL2.96 g/mL
21 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.= 18.7 (3 sig figs)
22 Sig Fig Practice #3 Calculation Calculator says: Answer 3.24 m + 7.0 m 100.0 g g76.27 g76.3 g0.02 cm cm2.391 cm2.39 cm713.1 L LL709.2 Llb lblblb2.030 mL mL0.16 mL0.160 mL