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?