ch. 3 scientific measurement ch. 3 scientific measurement
TRANSCRIPT
Ch. 3 Scientific Ch. 3 Scientific Measurement Measurement
MeasurementMeasurement
Quantitative informationQuantitative information Need a number and a unit (most of time)Need a number and a unit (most of time) Represents a quantityRepresents a quantity For example: 2 metersFor example: 2 meters
2 is number2 is number Meters is unitMeters is unit Length is quantityLength is quantity
Units compare what is being measured to Units compare what is being measured to a defined measurement standarda defined measurement standard
SI MeasurementSI Measurement
Le Systeme International d’Unites : SILe Systeme International d’Unites : SI System of measurement agreed on all System of measurement agreed on all
over the world in 1960over the world in 1960 Contains 7 base unitsContains 7 base units
We still use some non-SI unitsWe still use some non-SI units
Important SI Base UnitsImportant SI Base Units
Quantity Symbol Unit Abbreviation
Length l meter m
Mass m kilogram kg
Time t second s
Temperature T Kelvin K
Amount n mole mol
PrefixesPrefixes Prefixes are added to the base unit names to Prefixes are added to the base unit names to
represent quantities smaller or largerrepresent quantities smaller or larger
M mega 106 1,000,000 larger
k kilo 103 1,000 larger
c centi 10-2 1/100 smaller
m milli 10-3 1/1000 smaller
μ micro 10-6 1/1,000,000 smaller
LengthLength
SI unit: m SI unit: m use use cmcm a lot too a lot too kmkm is used instead of miles for is used instead of miles for
highway distances and car speeds in highway distances and car speeds in most countriesmost countries
MassMass
Measure of the quantity of matterMeasure of the quantity of matter SI unit: kg SI unit: kg use use gg a lot too a lot too mass vs. weightmass vs. weight
weight is the measure of gravitational pull on weight is the measure of gravitational pull on mattermatter
mass does not depend on gravitymass does not depend on gravity on a new planet, mass would be same but on a new planet, mass would be same but
weight could changeweight could change
Temperature ConversionsTemperature ConversionsFahrenheit to CelsiusFahrenheit to Celsius
329
5 C F
325
9F C
Celsius to Kelvin conversionsCelsius to Kelvin conversions
+273.15+273.15
→→
CC KK←←
-273.15-273.15
Temperature ConversionsTemperature Conversions
ExampleExample
What is 32°F in Kelvin?What is 32°F in Kelvin? freezing point of water!freezing point of water!
0)3232(9
5C
15.27315.2730 K
ExampleExample
What is 298 K in Fahrenheit?What is 298 K in Fahrenheit?
CC o25273298
FF 7732)25(5
9
Derived SI UnitsDerived SI Units
come from combining base unitscome from combining base units combine using multiplication or divisioncombine using multiplication or division
Example:Example: Area: A = length x widthArea: A = length x width
= m x m = m x m
= m= m22
VolumeVolume
amount of space occupied by objectamount of space occupied by object SI: mSI: m33 = m x m x m = m x m x m use use cmcm33 in lab a lot in lab a lot non-SI: non-SI:
1 liter = 1dm1 liter = 1dm33= 1000cm= 1000cm33
1 liter = 1000 mL1 liter = 1000 mL1cm 1cm 33= 1mL= 1mL
DensityDensity
ratio of mass to volumeratio of mass to volume SI:SI:
Other units: g/ cmOther units: g/ cm3 3 or g/ mLor g/ mL
volume
massDensity
3m
kg
characteristic property of substance (doesn’t characteristic property of substance (doesn’t change with amount ) because as volume change with amount ) because as volume increases, mass also increasesincreases, mass also increases density usually decreases as T increasesdensity usually decreases as T increasesexception: ice is less dense than liquid water so exception: ice is less dense than liquid water so it floatsit floats
ExampleExample
A sample of aluminum metal has a mass of A sample of aluminum metal has a mass of 8.4 g. The volume is 3.1 cm8.4 g. The volume is 3.1 cm33. Find the . Find the density.density.
Known Unknown
m = 8.4 g D = ?
V = 3.1 cm3
337.2
1.3
4.8
cm
g
cm
g
V
mD
Conversion FactorsConversion Factors ratio that comes from a statement of ratio that comes from a statement of
equality between 2 different unitsequality between 2 different units every conversion factor is equal to 1every conversion factor is equal to 1
dollarquarters 14
Example:Example:
statement of equalitystatement of equality
conversion factorconversion factor1
4
1
quarters
dollar
Dimensional AnalysisDimensional Analysis
Conversion FactorsConversion Factors
can be multiplied by other numbers can be multiplied by other numbers without changing the value of the without changing the value of the number number
since you are just multiplying by 1since you are just multiplying by 1
quartersdollar
quartersdollars 12
1
43
Example 1Example 1
Convert 5.2 Convert 5.2 cm to mmcm to mm
5.2 5.2 cm= 5.2 x 10 cm= 5.2 x 10 11mmmm = 52 mm = 52 mm Known:Known: 100 cm = 1 m100 cm = 1 m
1000 mm = 1 m1000 mm = 1 m Must use m as an intermediateMust use m as an intermediate
mmm
mm
cm
mcm 52
1
1000
100
12.5
Example 2Example 2
Convert 0.020 Convert 0.020 kg to mgkg to mg0.020 0.020 kg = 0.020 x 10 kg = 0.020 x 10 66 mg mg= 20,000 mg= 20,000 mg
Known:Known: 1 kg = 1000 g1 kg = 1000 g1000 mg = 1 g1000 mg = 1 g
Must use g as an intermediateMust use g as an intermediate
mgg
mg
kg
gkg 000,20
1
1000
1
1000020.0
Example 3Example 3
Convert 500,000 Convert 500,000 μμg to kgg to kg
500,000 500,000 μμg = 500,000 x 10 g = 500,000 x 10 -9-9 kg kg= 0.0005 kg= 0.0005 kg Known:Known: 1,000,000 1,000,000 μμg = 1 gg = 1 g
1 kg = 1000 g1 kg = 1000 g Must use g as an intermediateMust use g as an intermediate
kgg
kg
g
gg 0005.0
1000
1
000,000,1
1000,500
Advanced ConversionsAdvanced Conversions One difficult type of conversion deals with One difficult type of conversion deals with
squared or cubed unitssquared or cubed units
ExampleExample
Convert 3 dm Convert 3 dm 33 to cm to cm33
1dm =10 cm1dm =10 cm
3 dm 3 dm 33 = 3 x 10 cm x 10 cm x 10 cm= 3000 cm = 3 x 10 cm x 10 cm x 10 cm= 3000 cm33
ExampleExample
Convert: Convert: 2000 cm2000 cm33 to m to m33
OR
Known:Known:100 cm = 1 m100 cm = 1 m cmcm33 = cm x cm x cm = cm x cm x cmmm33 = m x m x m = m x m x m
3002.0100
1
100
1
100
12000 m
cm
m
cm
m
cm
mcmcmcm
33
3 002.0100
12000 m
cm
mcm
Advanced ConversionsAdvanced Conversions
Another difficult type of conversion deals Another difficult type of conversion deals units that are fractions themselvesunits that are fractions themselves
Be sure convert one unit at a time; don’t Be sure convert one unit at a time; don’t try to do both at oncetry to do both at once
Work on the unit on top first; then work on Work on the unit on top first; then work on the unit on the bottomthe unit on the bottom
ExampleExample
Convert 350 g/ mL to kg/LConvert 350 g/ mL to kg/L Top firstTop first
350 g to kg 350 g to kg 350 g= 350 x 10 350 g= 350 x 10 -3-3 kg= .35 kg kg= .35 kg Bottom part afterBottom part after
1mL to L1mL to L1mL= 1x 10 1mL= 1x 10 -3-3 L= 0.001 L L= 0.001 L Result:Result:350 g/ mL = .35 kg/ 0.001L= 350kg/ L350 g/ mL = .35 kg/ 0.001L= 350kg/ L
Combination ExampleCombination Example
Convert 7634 mg/mConvert 7634 mg/m33 to Mg/L to Mg/L
TopTop7634 mg= 7634 x 10 7634 mg= 7634 x 10 -9-9 Mg= 0.000007634 Mg Mg= 0.000007634 Mg
BottomBottom1m= 10 dm1m= 10 dm1 m1 m33= 10 dm x 10 dm x10 dm= 1000 dm = 10 dm x 10 dm x10 dm= 1000 dm 33 = 1000 L = 1000 L
Result:Result:7634 mg/m7634 mg/m3 3 = 0.000007634 Mg/ 1000 L= 0.000000007634 Mg/L= 0.000007634 Mg/ 1000 L= 0.000000007634 Mg/L= 7.634 x 10 = 7.634 x 10 -9-9 Mg/L Mg/L
Accuracy vs. PrecisionAccuracy vs. Precision
AccuracyAccuracy- closeness of measurement to - closeness of measurement to correct or accepted valuecorrect or accepted value
PrecisionPrecision- closeness of a set of - closeness of a set of measurementsmeasurements
Accuracy vs. PrecisionAccuracy vs. Precision
Percent Error vs. Percent DifferencePercent Error vs. Percent Difference
Percent Error:Percent Error: Measures the accuracy of an Measures the accuracy of an
experimentexperiment Can have + or – valueCan have + or – value
%100accepted
lexperimetaaccepted
Percent Error vs. Percent DifferencePercent Error vs. Percent Difference
Percent Difference: Percent Difference: Used when one isn’t “right”Used when one isn’t “right” Compare two valuesCompare two values Measures precisionMeasures precision
%1002 and 1 valueof average
2 value1 value
ExampleExample
Measured density from lab experiment is Measured density from lab experiment is 1.40 g/mL. The correct density is 1.36 1.40 g/mL. The correct density is 1.36 g/mL. g/mL.
Find the percent error.Find the percent error.
%94.210036.1
1.40-1.36 error %
ExampleExample
Two students measured the density of a Two students measured the density of a substance. Sally got 1.40 g/mL and Bob got 1.36 substance. Sally got 1.40 g/mL and Bob got 1.36 g/mL.g/mL.
Find the percent difference.Find the percent difference.
%90.2100
21.361.401.36-1.40
difference %