2Why is Chemistry important? In our daily lives:New materialsNew pharmaceuticalsNew energy sourcesFood suppliesCan you think of anything else?
3ChemistryIs the science that deals with the materials of the universe and the changes that those materials undergo
4Chemical Changes What are some examples of chemical changes? Iron rustingWood burningFood cookingGrape juice fermentingPlants growingHow do we know that these are chemical changes?
5Steps in the Scientific Method ObservationsQuantitative vs QualitativeQuantitative – measurement involves a number and a unitFormulating HypothesesPossible explanation for the observationPerforming ExperimentsGathering new information to decide whether the hypothesis is valid
6Quantitative & Qualitative Observations Qualitative Quantitativered book 4 quartersround tire 6 wheelswooden desk 24 studentsmetal chair 5 atomsaluminum foil 65°Cglass square 2” x 4” x 8”rough board 2 graduated cylinders
7Outcomes over the Long Term Theory (Model)A set of tested hypotheses that give an overall explanation of some natural phenomenonNatural LawThe same observation applies to many different systemsEx. Law of Conservation of Mass
8Law vs TheoryA law summarizes what happens; a theory (model) is an attempt to explain why it happens
10Problems with the scientific method Scientists must be objective when using the scientific method. The scientific method is affected by:Profit motives Religious BeliefsWars Misinterpretation of DataBudgets EmotionsFads PrejudicesPolitics Peer Pressure
11Scientific Terminology What is the difference between a hypothesis and a theory?What is the difference between an observation and a theory?What is the difference between a natural law and a theory?
12The Fundamental SI Units Physical Quantity Name Abbreviationmass kilogram kglength meter mtime second stemperature Kelvin KElectric Current Ampere AAmount of Substance mole molLuminous Intensity candela cd
13SI Prefixes Common to Chemistry Unit Abbr.ExponentMegaM106Kilok103Decid10-1Centic10-2Millim10-3Micro10-6Nanon10-9Picop10-12
14Uncertainty in Measurement A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.Measurements are performed with instrumentsNo instrument can read to an infinite number of decimal places.
15Precision and Accuracy Accurate and precisePrecise, but not accurateNeither accurate not preciseAccuracy refers to the agreement between the measure quantity and the accepted valuePrecision refers to the degree of agreement of several repeated measurements (made in the same manner) to each other.
16Types of Error Random Error (Indeterminate Error) – Measurement has an equal probability of being high or lowSystematic 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
17Rules for Counting Significant Figures Non-zero integers always count as sig. fig.34564 sig figs
18Rules for Counting Significant Figures ZerosLeading Zeros do not count as sig figs0.04863 sig figs
19Rules for Counting Significant Figures ZerosCaptive Zeros always count as sig figs16.074 sig figs
20Rules for Counting Significant Figures ZerosTrailing Zeros are significant only if the number contains a decimal point.9.3004 sig figs
21Rules for Counting Significant Figures Exact Numbers have an infinite number of significant figures.1 inch = 2.54 cm
22Practice Counting Significant Figures m17.10 kg100,890 L3.29 x103 scm3, 200, 0005 sig figs4 sig figs3 sig figs2 sig figs
23Rules for Significant Figures in Mathematical Operations Multiplication and Divisionnumber of sig figs in the results equals the number of sig figs in the least precise measurement used n the calculation (the one with the lowest number of sig figs).6.38 x 2.0 = 12.7613 (2 sig figs)
24Practice for Significant Figures in Mathematical Operations Answer23 m24.22 g/cm30.05 cm2240 m/s5870 lb·ft2.96 g/mLCalculationCalculator Says3.24 m x 7.0 m22.68 m2100.0 g ÷ 23.7 cm3g/cm30.02 cm x cmcm2710 m ÷ 3.0 sm/slb x 3.23 ftlb·ft1.030 g ÷ 2.87 mLg/mL
25Rules for Significant Figures in Mathematical Operations Addition and SubtractionThe number of decimal places in the result equals the number of decimal places in the least precise measurement=18.7 (3 sig figs)
26Practice for Significant Figures in Mathematical Operations CalculationCalculator Says3.24 m m10.24 m2100.0 g cm376.27 g/cm30.02 cm cm2.391 cm2713.1 m – sm/slb lblb·ft2.030 mL mL0.16 g/mLAnswer10.2 m76.3 g2.39 cm709.2 Llb0.160 mL