Name: Per.: Date: Assignment #: Chemistry: Scientific ......• Ex 2/ Write the two possible...
Transcript of Name: Per.: Date: Assignment #: Chemistry: Scientific ......• Ex 2/ Write the two possible...
Name:___________________________________________Per.:______Date:_________________________Assignment#:_______Chemistry:ScientificMeasurementsNotesMeasurements
• Weoftentakemeasurementsinchemistrylabs• Areourmeasurementsaccurate?
o Thisdependson:§ Thereliabilityofthemeasuringinstrument§ Thecarewithwhichitisread–thisisdeterminedbyYOU!
Accuracyvs.Precision
• Itisnecessarytomakegood,reliablemeasurementsinthelab• Accuracy–howcloseameasurementistothe________________________________• Precision–howclosethemeasurementsare_________________________________(reproducibility)
SignificantFigures
• SignificantFigures=_____________________________________________________________________________________________________________________________________________
• Measurementsmustbereportedtothecorrectnumberofsignificantfigures
• Ifyoudon’tusethecorrectsigfigs,youranswerisincorrectL
RulesforSigFigs
• RulesforCountingSigFigs1) ____________________________________arealwayssignificant
Ex/3456has_________sigfigs2) ____________________________________areNOTsignificant
Ex/0.0486has_______sigfigs3) Zeroes____________________________significantdigitsarealsosignificant
Ex/16.07has_______sigfigs4) __________________________________________aresignificantonlyifadecimalispresent
Ex/9.300has_______sigfigsEx/0.03010has_______sigfigs
5) ____________________________anddefinedquantitieshave_____________________sigfigsEx/23people,or425thumbtacksEx/60minutes=1hour
6) ScientificNotationX×10n
• Pair-Share-Respond:o _____________________o _____________________o _____________________o _____________________
o _____________________o _____________________o _____________________
RoundingCalculatedAnswers• Ingeneral,acalculatedanswercannotbemoreprecisethantheleastprecisemeasurementfrom
whichitwascalculated• Everheardthatachainisonlyasstrongastheweakestlink?• Sometimes,calculatedvaluesneedtoberoundedoff1) Determinehowmanysigfigsareneeded2) Roundyouranswertothecorrectnumberofsigfigs• AddingandSubtracting
o Roundtothenumberwiththe____________________________________________________________________o Ex/12.25m+349.0m+8.24m=_____________________
• MultiplyingandDividing
o Roundanswertothe_______________________________________________________________presento Ex/6.38×2.0=_____________________o Ex/2.10meters×0.7meters=_____________________
• Pair-ShareRespondAnswers:
o _____________________o _____________________o _____________________o _____________________o _____________________o _____________________
ScientificNotationReview
• Howwideisouruniverse?• 210,000,000,000,000,000,000,000miles• That’s22zeroes• Whennumbersarethislarge,itiseasiertowritetheminscientificnotation
o à2.1×1023miles• Scientificnotationexpressesanumberintheform:
• Rules:
1. Movedecimalpointafterthe__________________________________________,andincludeallsignificantdigits
2. _____________________=numberofplacesyoumovedthedecimal3. Movedleftà_____________________exponent.Movedrightà_____________________exponent.4. WriteasM×10n
• Examples1) 0.0000000902
Wherewouldthedecimalgotomakethenumberbetween1and10?______________Thedecimalwasmovedhowmanyplaces?______________Imovedright,somyexponentisnegative.Answer:____________________________
• TryThese:Writeinscientificnotation
1) ____________________________2) ____________________________
3) ____________________________4) ____________________________
Units
• Weuseunitstoexpressourmeasurements• TheInternationalSystemofUnits(AKAMetricsystem)isastandardsystem• Commonbaseunitsinchemistry:
o Length:____________________________o Mass:____________________________o Temperature:____________________________o Time:____________________________o Amount:____________________________o Energy:____________________________o Volume:____________________________
• Non-SIunits(Liter,Celsius)andderivedunits(miles/hour,grams/mL)aresometimesalsoused
Conversions
• IntheSIsystem,baseunitsareusedandcaneasilybeconvertedsincetheyarefactorsof10.
o Example:o 1000mm=103mm=1mo 100cg=102cg=1g
• First,writewhatyoustartwith• Second,drawaconversionfactor(ratio).Thisiscalleddimensionalanalysis.• Example:103mL=1L
• Theseconversionfactorsaredefined,andhaveunlimitedsignificantfigures• DONOTusetodeterminethenumberofsigfigsinyourfinalanswer• Onlyusegivenmeasurements• Ex1/Writethetwopossibleconversionfactorsforkilogramsandgrams
• Ex2/Writethetwopossibleconversionfactorsforcentimetersandmeters
• Ex3/Convert13inchestoyards.
• Ex4/Convert12.0inchestocm
• Ex5/Express750dginkilograms
• Ex6/Express9.7kgincentigramsOtherCalculations
• Ex7/Change15meters/hourtounitsofcentimeters/second
• Density=________________________________________• Commonunitsare________________orpossibly________________(org/Lforgas)• Densityisaphysicalproperty,anddoesnotdependuponsamplesize• Ex8/Apennyhasamassof3.1gandavolumeof0.35cm3.Calculateitsdensity.
• Whathappenstothedensityasthetemperatureofanobjectincreases?o Massremainsthesameo Mostsubstancesincreaseinvolumeastemperatureincreaseso Thus,densitygenerallydecreasesasthetemperatureincreases
• Waterisanimportantexceptiontothepreviousstatement.Overcertaintemperatures,thevolumeofwaterincreasesasthetemperaturedecreases(doyouwantyourwaterpipestofreezeinthewinter?)
o Doesicefloatinliquidwater?Whyorwhynot?