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Chemistry Notes.docx

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CHEM 208
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Module1BasicsLambertLamLesson 11Scientific Method1 Steps of the Scientific MethodThe scientific method performing a study in organized steps consists of1Performing experiments2Making observations3Proposing a hypothesis based upon the observation made 4Confirming the hypothesis by repeated experimentation5Proposing a scientific lawStep 1Performing ExperimentsAn experiment is a set of steps procedures that are performed under controlled conditions to propose or test a hypothesisStep 2Making ObservationsObservations a key factor in scientific studies as well as in everyday life can be classified as oQualitativeobservation does not use numbers The flower is purpleBubbles are produced when lemon juice is added to baking sodaoQuantitativeobservation is a measurement It has two componentsA measured quantity numerical value with an appropriate unitObserved temperature measured using a thermometer for the liquid was found to be 33CIn this case the measured quantity is temperature and the appropriate unit is CStep 3Proposing a HypothesisA hypothesis is a tentative explanation to account for the observations of an experiment A hypothesis is valid provided that ones assumptions to explain the observations of an experiment can be testedStep 4Confirming the HypothesisThe validity of the hypothesis needs to be confirmed via repeated and controlled experiments In order to accept a hypothesis there must be no inconsistencies between the hypothesis and the experimental observations In the event of any inconsistencies steps 1 through 4 must be repeatedStep 5Proposing a Scientific LawBy repeatedly performing experiments and modifying the hypothesis to account for the observations from the experiments one is able to propose a scientific lawExpression of Numerical ValueCertain rules apply to the expression of the numerical value and the system of units used in scientific measurements These includeScientific notationSignificant figuresSI system of units2 Scientific NotationScientific notation is a very convenient way of expressing very large or very small numbers and at the same time provides a method of increasing efficiency in scientific calculationsnIt is a mathematical expression in which a number is expressed as N x 10where N contains only one nonzero digit to the left of the decimal and n is an integerMeasurementScientific Notation0123g123 x 10g310004 mL10004 x 10mL300012 mg12 x 10mg15162832 x 10L2832 x 10L7210 million kg210 x 10kg3 Significant Measures DigitsEvery measurement and thus all of the calculations performed by using such measurements always have some uncertaintya characteristic of any measurementThis is due to experimental error In the case of measuring devices the last digit of the measurement is uncertainSignificant figures sig fig in a measured number include all certain digits and one uncertain digitThe concept of significant figures isUsed to indicate the precision reproducibility closeness of measurements of a measurement or that of a calculated result using much measurementsDoes not apply to counted items such as exact numbers eg 5 cars 3 houses and defined conversion factors eg 1 inch254 cm 1 cal4184 JThese have an infinite number of significant figuresRules of Determining Significant Figures DigitsRule 1All nonzero digits are significant figuresMeasurement of sig fig13562 g5236 cm3179871 kg6Rule 2Counting begins from the left with the first nonzero number thus leading zeros are not significantMeasurement of sig fig0056 mL20000356 L300225 kg3Rule 3Zeros between nonzero digits are counted as significant figuresMeasurement of sig fig1056 g43078 cm 4
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