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Chemistry

CHEM 208

All Professors

Fall

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Module 2 The Scientific Method and MatterThe Scientific MethodIn a standard visit to a medical clinic tests are performed making observations that help the physician in diagnosing the probable cause of the problem proposing a hypothesis Next the medication is prescribed and finally the ailment is checked in due course to ensure that the problem has been solved testing the hypothesis by experimentStep 1 Performing Experiments An experiment is a set of steps procedures that are performed under controlled conditions to propose or test a hypothesis Step 2 Making ObservationsObservations key factor in scientific studies as well as in everyday life can be classified asQualitative does not use sEx The Flower is PurpleBubbles are produced when lemon juice is added to baking sodaQuantitative is a measurement Has two components A measures quantity numerical value with an appropriate unitEx Observed temperature measured using a thermometer for the liquid was found to be 33 degree celcius Measured quantitytemperature and appropriate unit is degrees celcius Step 3 Proposing a Hypothesis based upon the observations madeA 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 tested Step 4 Confirming the Hypothesis by repeated experimentationThe validity of the hyp needs to be confirmed via repeatedcontrolled experimentsIn order to accept a hyp there must be no inconsistencies between the hypthe experimental observationsIf there are inconsistencies steps 14 must be repeatedStep 5 Proposing a Scientific LawBy repeatedly performing experimentsmodifying the hypothesis to account for the observations from these experiments one Is able to propose a scientific law Numerical ValuesExpression of Numerical ValueCertain rules apply to the expression of the numerical value and the system of units used in scientific measurements each to be discussed further on the following slidesThese includeScientific notation Convenient way of expressing very large or very small numbers and at the same time provides a method of increasing efficiency in scientific calculations nMathematical expression in which ain expressed as N x 10 Powers of ten must be used 10 raised to a certain powerN can be anyother than zero but can only have one digit before the decimal 456 but not 7665 or 0456 n can be any whole number without decimal2 3Ex 5984659846 x 10 and 0007676 x 10 Significant figures digitsEvery measurement always has some uncertainty due to experimental error In the case of measuring devices the last digit of the measurement is uncertain Significant figures sigfig in a measured number include all certain digits and one uncertain digitThe concept of significant figure isUsed to indicate the precision reproducibility closeness of measurements of a measurement or that of a calculated result using such measurementsDoes not apply to counted items such as exact numbers ex 5 cards 3 houses and defined conversion factors ex 1 inch254 cm 1 cal4184 JThese have an infinite number of significant figuresRule 1 All nonzero digits are significant figures Rule 2 Counting begins from the left with the first nonzero number Leading zeros are not significant Rule 3 Zeros between nonzero digits are counted as significant figuresRule 4 Terminal zeros zeros to the right of a numberThese are always significant if the value contains a decimal point ex 1Terminal zeros in other cases may or may not be significant For example a measured value given as 200 cm does not signify anything regarding theof significant figuresIn such cases sometimes a decimal point makes the zeros significant but mostly scientific notation is used ex 2Chemical CalculationsIn calculations involving measured values with a certain number of significant figures the number of significant figures in the final answer depends on the operations performedRule 1 In addition and subtraction of measured quantities the final answer contains the same number of decimal places as are in the measurement with least number of decimal places least precise measurementEX 250 g2241 g1234 g486 gRule 2 in multiplicationdivision of measured quantities the final answer contains the sameof significant figures as are in the measurement with the leastof significant figures Ex 920 g x 2450 g225 gRule 3 In the final answer of a calculation involving exact numbers unit conversion factorsconstants theof significant figures is dictated by the measured quantity involved Exact numbers unit conversion factorsconstants have no effect on the number of significant figures

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