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1 Chemistry 11 Unit 1: SI units and unit conversion Hebden p. 9-40) SI#units# "SystemeInternational",orSI#Units,isastandardizedsystemofmeasurementbasedoninternationally agreeddefinitions. Thereareseveralbase#units. Quantity Unit Symbol Length Mass Amountofsubstance mole mol Time Temperature Energy joule J Electriccurrent ampere A Volume aremadebyusingmultiplethebaseunits.forexample: Velocity= withaunitm/s) Density= withaunitkg/l) MolarityConcentration)= withaunitmol/l) WhatdoyounoticeaboutunitslikemLmililitre),µmmicrometer),ηsnanosecond)? Theseunitsaremadeof andbaseunit. Usingaprefixandbaseunittougherallowustoworkvery or numbers moreconveniently. Eachprefixrepresentsamultipleof10 x.

2 Memorize:,,,,,and fortherestoftheyear!) Explorethescaleofuniversehttp://htwins.net/scale2/) Ms.Yajimaisabout157cminheight.Howmanymisthat? 157cm=1.57m Canyoufillintheblanktoshowthestep? 157cmXm=1.57m cm E.g.,Usethesamemethodtoconvertanaverageheightofminionsfrom1050mmintom. 1050mmXm= m mm E.g.,Howmanygarethereinanaveragemassofbananas0.116kg)? 0.116kgXg= g kg Thefractionusedabovetochangeoneunitintoanotheriscalledtheunit#conversion#factor.Unitconversion factorsrepresentrelationshipbetweentwounits. E.g.,Writeunitconversionfactorbetweenthefollowingunits: 1. cmandm 2. mmandm 3. µgandg 4. ηsands Unitconversionbetweentwonon`baseunitsrequiresmultiplefactorsinthestep.First,changethegiven unittonon`prefixunit,thenchangetothedesiredunit. E.g.,Howmanykgarethereinanaveragemassofanadulthumanbrain mg)? mgXgXkg= kg mg g 2

3 Q:Howmanyμgaretherein7kg?Usetwoconversionfactorsbecauseitisaconversionbetweentwonon` baseunits.dokg!g!μg) Q:Convert72μsintoms.Usetwoconversionfactorsbecauseitisaconversionbetweentwonon`base units.doμs!s!ms) Challenge#Q:Convert100m/μsintokm/s.Dom!km,andμs!s) Q:Howmanyminutesaretherein2hours? Whatistheconversionfactorhere?i.e.,Whatistherelationshipbetweenhoursandminutes?)!Beginwiththevaluethatisgiven. 2hoursX = Note:&You&may&not&always&know&the&conversion&factor.&In&that&case,&read&the&question&carefully&to&unlock&the& secret&message.&you&can&still&follow&the&same&steps.& Q:Ifacarcango80kmin1hr,howfarcanthecargoin8.5hr? Q:If0.200mLofgoldhasamassof3.86g,whatisthemassof5.00mLofgold? 3

4 Density Densityisanexampleofderivedquantity.Itisanumbermadebycombiningtwoormoreothervalues.Densityis definedasmassdividedbyvolumeormassovervolume).inotherwords:!"#$%&'! =!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Inthelabexperiment,youwillfindthedensityofagivensamplethencompareyourresultwiththeacceptedvalue. Reading#a#Value Step1 Whenreadingavalueoffglasswareorotherinstruments), firstfigureout. Forexample,inthisgraduatedcylinder,eachspacingrepresents1mL. Step2 Readthevalueusingthe #of#the# Itisapproximately36mL,butitisalittlebitmore.Howmuchmore? NOTE:Generally,dependingonhow visiblyapart thespacingsare, youcanestimatethelastdigitto1/10 th to1/5 th orevenless)ofthe spacings Thebottomofthemeniscuslookslikeitasexactlyhalf`waybetween 36mLand37mL.Therefore,#the#reading#is# #ml Q.Readtheburettereading. Eachspacingis ml.butthenumberincreasesgoingdown.wow! Estimatedvalueis ml,butitisabitmorethan ml. Thebottomofthemeniscuslookslikeslightlybelow1.4mL,soIamgoingtoreaditas 1.41mL.#Butyoumayreaditas1.42mL,whichisacceptable.Answersuchas1mL, 1.4mL,1.410mL,1.415mLareNOTacceptable.Acceptablevaluesare ml, mlor ml. Noticethethirdnumber3 rd significantfigure)isnotreallyfixedsoitiscalledthe #digit. Inthisreading,wehave2certaindigits,and1uncertaindigit NOTE:Inmostofyourreadings,every#digit#is#certain#except#for#the#last#one. 4

5 Significant#Figures AtanOlympictrialsrace,arunnerwasclaimedtohavecrossedthefinishlineatatimeof #seconds.A stopwatchwasusedtotimetherunnerduringtherace.whatiswrongwiththerecordedrunner stime? Ifthestopwatchcanonlyreadto0.1s,thenitissillytoclaimthatthetimeis s.Thestopwatch can tmeasurethetimeto7decimalplaces.therefore,thelastdigits916847)haveno#significance!they arenotimportant. What%is%a%significant%figure? Significant#figure:isameasuredand digit. Rules#of#Counting#Significant#f=Figures: 1. Anynon zeronumberisasignificantfigure. Eg. 35.2Thisvaluehas sigfigs. 2. Leading#zeroesareNOTsignificantbecauseitistheretoplacethedecimalpoint. Eg sigfigs) 3. Zeroesin#betweennon zeronumbersaresignificant. Eg. 205 sigfigs) sigfigs) 4. Trailing#zeroesthe endingzeros )aresignificant..? Eg sigfigs) sigfigs) Hmmmwell.#Trailing#zeroesareONLYsignificantwhena#decimal#pointisshown.weassumethatthelast digitsarezeroesbecausetheyareroundedoff) Eg. 0.1 sigfigs) 0.10 # sigfigs) 1100 # sigfigs) 10 # sigfigs) # sigfigs) 10. # sigfigs) # sigfigs) 5. Definedvalueshave #numberofsigfigs. Eg.1km=10 3 m infinitenumberofsigfigs) Eg.Dozen=12 infinitenumberofsigfigs) Scientific#Notation: Fromdecimalpointoftheoriginalnumber,counthowmanytimesthepointneedstomovetogetonlyone digitleftofthepoint. Moveleft= exponent Moveright= exponent 5

6 Eg.Change358123intoscientificnotation. Eg.Change0.1135intoscientificnotation. # # Note:Onlycountthenumberofsignificantfiguresinthe partofthescientificnotation. # Rounding#the#Numbers#to#the#Correct#Number#of#Sig#Figs Startcuttingdigitsfromtherightanddecidewhichlastdigittokeep.Leaveitasisifthenextdigiton therightislessthan5.increaseitby1roundingup)ifthenextdigitontherightismorethan5. Q.Roundto3significantfigures: ! Multiplying#and#Dividing#Numbers: Aftermultiplyingordividingnumbers,round#offtheanswertotheLEAST#numberofsignificantfigures containedinthecalculation. Eg X3.000=6.00 # 3s.f. 4s.f. 3s.f. NOTE:&You&should&keep&all&your&digits&used&on&your&calculator&during&the&calculations.&&Only&the&final& answer&should&be&rounded!!! Adding#and#Subtracting#Numbers: Afteraddingorsubtractingnumbers,round#offtheanswertotheLEAST#numberofdecimalplaces containedinthecalculation. Eg. Add12.56and125.8together. Eg decimalplaces decimalplace finalanswerroundedto1decimalplace! 6

7 Accuracy#and#Precision InEnglishclass,boththesetermsmeanverysimilarthings;butinscienceitisnotso! isdeterminedbyhowcloseyourvalueistothetrueorcorrect value. isdeterminedbyhowmanys.f.yourvaluehasandbyhowoftenyour valuesarerepeated. Eg.Whenmeasuringthedensityofsilversample,densitywasmeasuredtobe8.1g/mL,8.0g/mLand 7.8g/mL.Ifthe correct densityofsilveris10.5g/ml,areyourvaluesprecise,accurateorneither? Trythefollowingexampletodetermineifitisaccurate,precise,bothorneither. Ss Ss Ss Ss 7

8 Name: Date: Block: CHEMISTRY 11 UNIT CONVERSIONS Make sure to show all steps including all units, and box your final answer. 2. The average distance from the earth to the moon is 384Mm. Express this distance in mm. 3. The mass of an average grain of salt is 115 microgram. Express this mass in grams. 4. The thickness of this paper is 40.5!m. What is the thickness of the paper in km?! 1

9 5. The speed of light is 3.0 X cm/s. Sunlight takes 8.29 minutes to travel from the surface of the sun to the earth. What is the distance of the earth from the sun in km? 6. A car travels 7.50 km per litre of gasoline. Express this gas mileage in m/ml. 7. The average distance from the earth to the moon is 384 Mm. If sound travels at a speed of 385m/s, how many minutes would it take for an astronaut s message to reach the earth?! 2

10 Name Date Class 53 MATH HANDBOOK TRANSPARENCY MASTER Scientific Notation 1 Use with Appendix B, Scientific Notation Scientists need to express small measurements, such as the mass of the proton at the center of a hydrogen atom kg), and large measurements, such as the temperature at the center of the Sun K). To do this conveniently, they express the numerical values of small and large measurements in scientific notation, which has two parts. A number in which only one digit is placed to the left of the decimal N 10 n An exponent of 10 by which the number is multiplied Thus, the temperature of the Sun, 15 million kelvins, is written as K in scientific notation. Positive Exponents Express in scientific notation. Copyright Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc. Each time the decimal place is moved one place to the left, Negative Exponents Express in scientific notation. Each time the decimal place is moved one place to the right, the exponent is increased by one. the exponent is decreased by one. Math Handbook Transparency Masters Chemistry: Matter and Change 91

11 Name Date Class 54 MATH HANDBOOK TRANSPARENCY WORKSHEET Scientific Notation 1. Express each of the following numbers in scientific notation. a Use with Appendix B, Scientific Notation b c d. 56 million e. 2/10 f g h i j. 12 thousandth 2. Express each of the following measurements in scientific notation. a. speed of light in a vacuum, m/s b. number of seconds in a day, s c. mean radius of Earth, 6378 km d. density of oxygen gas at 0 C and pressure of 101 kpa, g/ml Copyright Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc. e. radius of an argon atom, m 92 Chemistry: Matter and Change Math Handbook Transparency Worksheets

12 Name 55 Scientists very often deal with very small and very large numbers, which can lead to a Pf confusion when counting zeros! We have learned to express these numbers as powers 10. Scientific notation takes the form of M x 1 On where 1 I M < 10 and 'n" represents the number of decimal places to be moved. Positive n indicates the standard form is a large number. Negative n indicates a number between zero and one. Example 1 : Convert 1,500,000 to scientific notation. We move the decimal point so that there is only one digit to its left, a total of 6 places., 1,500,000 = 1.5 x lo6 Example 2: Convert to scientific notation. For this, we move the decimal point 5 places to the right = 2.5 x 105 Note that when a number starts out less than one, the exponent is always negative.) Convert the following to scientific notation. Convert the following to standard notation. 5. 2,2x105 = 10. 4x100 = chemistry IF8766 Fair, Inc.

13 Name Date Class 57 MATH HANDBOOK TRANSPARENCY MASTER Operations with Scientific Notation 2 Use with Appendix B, Operations with Scientific Notation Addition and Subtraction Before numbers in scientific notation can be added or subtracted, the exponents must be equal. Not equal Equal ) ) ) ) The decimal is moved to the left to increase the exponent ) Multiplication When numbers in scientific notation are multiplied, only the number is multiplied. The exponents are added. Copyright Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc ) ) 2.00)4.00) Division When numbers in scientific notation are divided, only the number is divided. The exponents are subtracted Math Handbook Transparency Masters Chemistry: Matter and Change 93

14 Name Date Class 58 MATH HANDBOOK TRANSPARENCY WORKSHEET Operations with Scientific Notation 2 Use with Appendix B, Operations with Scientific Notation 1. Perform the following operations and express the answers in scientific notation. a ) ) ) ) ) ) ) b ) ) ) ) ) ) ) c ) ) ) ) ) ) ) d ) ) ) ) ) ) ) e ) ) ) ) ) ) ) f ) ) ) ) ) ) ) Perform the following operations and express the answers in scientific notation. a ) ) ) ) 4.3)2.0) b ) ) ) ) 6.0)1.5) ) c ) ) ) ) 1.5)8.0) ) d. e. f / / / / ) ) / ) ) 6.48/2.4)1.8) ) Copyright Glencoe/McGraw-Hill, a division of the McGraw-Hill Companies, Inc. 94 Chemistry: Matter and Change Math Handbook Transparency Worksheets

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17 Chemistry 11 Density Lab Names: Date: Purpose To measure the density of metal samples and compare the experimental results to the accepted values. Procedure 1. Fill a graduated cylinder with tap water about halfway up. 2. Record the initial volume of water with a correct number of digits. 3. Obtain a sample of metal or other material) and record its name. 4. Place the metal into the cylinder. 5. Measure and record the final volume of water. Take out the sample out of the cylinder and dry it with a paper towel. 6. Using a balance, weigh the mass of the sample. 7. Repeat from step 3 to 6 until you have at least three different measurements. Safety Precautions Equation The formula for density is: Data and Observation Metal used = Sample Transparency Color State Sample Mass g) Initial Volume ml) Final Volume ml) Change in Volume ml) Density g/ml) Average Density g/ml) % Error 1

18 Calculation 1. Calculate the density of each metal and fill it in the table. Show one sample calculation for density. Show all steps): 2. Compare your experimental measurement of the average density with the theoretical value from the table below. Use the equation below to calculate percent error. %!!""#"! =!!"#$%&'$)*+!!"#$%!!!h!"#!$%&'!!"#$%!h!"#!$%&'!!"#$% 100% Show calculation steps for % error. Element Symbol Theoretical Density g/ml) Nickel Ni 8.90 Aluminum Al 2.70 Chromium Cr 7.15 Platinum Pt 21.5 Copper Cu 8.96 Gold Au 19.3 Iron Fe 7.87 Silver Ag 10.5 Lead Pb 11.3 Tin Sn 7.26 Magnesium Mg 1.74 Tungsten W 19.3 Zinc Zn List two reasons why the experimental values are different from the theoretical value. This is called the source of error. Conclusion 2