Chemistry Chapter 3
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Transcript of Chemistry Chapter 3
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Chemistry Chemistry Chapter 3Chapter 3
Scientific MeasurementScientific Measurement
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Scientific NotationScientific NotationConvert to or from Scientific Convert to or from Scientific Notation:Notation:
A) 2412.41 x 102
B) 60156.015 x 103
C) 0.01621.62 x 10-2
D) 0.5125.12 x 10-1
E) 6.62 x 102
662
F) 3.4 x 10 -3
0.0034
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Accuracy -how close measurements are to the correct or accepted value.
Precision - closeness of a set of measurements.
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Percent error – compares the accuracy of an individual value or average values to the correct or accepted value.
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% error = Accepted value – Experimental value x 100% Accepted value
STAAR CHART FORMAT
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Example: What is the percent error for a Example: What is the percent error for a mass measurement of 17.7g, given that the mass measurement of 17.7g, given that the
correct value is 21.2g?correct value is 21.2g?
% error = 21.2g – 17.7g x 100% = 21.2g
16.5%16.5%
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Significant Figures RulesSignificant Figures Rules1. Nonzero Digits – every nonzero
digit is significant.
Ex: a) 32.8 m has three sig figs b) 981.78 km has five sig figs
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2. Sandwich zeros – zeros appearing between nonzero digits are significant.
Ex: c) 101.2 g has four sig figs d) 50.1 L has three sig figs
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3. Placeholder – leftmost zeros appearing in front of nonzero digits are not significant.
Ex: e) 0.000007 has one sig fig f) 0.0003809 has four sig figs
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4. Trailer zeros – zeros at the end of a number and to the right of the decimal point are significant.
Ex: g) 2000. m has four sig figs h) 34.0 mL has three sig figs
Uncertainty in Measurement
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STAAR CHART FORMAT FOR STAAR CHART FORMAT FOR SIG. FIGS.SIG. FIGS.
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RoundingRounding
*The calculated value cannot be more precise than the measured values used to obtain it.
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Example: Round each measurement to Example: Round each measurement to the three sig. figs.the three sig. figs.
a) 45.89m 45.9m
b) 3004 m3.00 x 103m
c) 17.32 cm 17.3 cm
d) 20019 L2.00x104 L
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Rounding – Addition and Rounding – Addition and SubtractionSubtraction
Round the answer to the same number of decimal places (not digits) as the measurement with the least number of decimal places.
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Example: Subtract 2.6103m Example: Subtract 2.6103m from 5.44m.from 5.44m.
5.44 m - 2.6103 m 2.8297 m
2.83m2.83m
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Rounding – Multiplication and Rounding – Multiplication and DivisionDivision
Round the answer to the same number of sig. figs as the measurement with the least number of sig. figs.
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Example: Multiply 2.4 mExample: Multiply 2.4 m22 and and 15.82m.15.82m.
2.4 m2 x 15.82 m = 37.968 m3
38 m38 m33
Extra Practice
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SI Measurement – Le Systeme International d’Unites
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7 SI Base Units7 SI Base Units Quantity Quantity
SymbolUnit Name Unit
Abbreviation
Length l meter mMass m kilogram kgTime t second sTemperatu
reT Kelvin K
Amount of Substance
n mole mol
Electric Current I ampere ALuminous
IntensityIv candela cd
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SI PrefixesSI Prefixes Prefi
xUnit
abbreviation
Exponential
factor
Example
kilo k 103 1 kilometer(km)= 1000 m
100 1 meter (m)
deci d 10-1 10 decimeter(dm) = 1 m
centi
c 10-2 100 centimeter (cm) = 1m
milli m 10-3 1000 millimeter (mm) = 1m
micro
u 10-6 1000000 micrometer (um) =1m
nano
n 10-9 1000000000 nanometer (nm) = 1m
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Mass – measure of the quantity of matter (SI unit is kg).
The gram, g, is ideal for expressing masses of small objects such as a beaker.
For even smaller masses like weighing out chemicals the milligram is used.
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Mass vs WeightMass vs Weight
Mass is the measure of the amount of matter, whereas weight is the measure of the gravitational pull on matter.
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Derived units are a combination of SI base units.
*Volume is the amount of space occupied by an object. The derived unit for volume is cubic meters, m3. (Volume = l x w x h)
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Figure 01.20Figure 01.20
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Density is a derived unit. It is mass divided by volume.
density = mass or D = m volume V
The SI units are kg/m3
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Density…:Density…:
• is a physical property of a substance.• does not depend on the size of the
sample.• As the mass of the sample increases
so does the volume.
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Density of a substance determines whether it floats or sinks in a liquid.
For instance, ice has a density of 0.92 g/mL, which is less than that of water (0.998 g/mL). Since ice is less dense, it will float on water.
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Example: The density of water is 0.998 g/mL. If Example: The density of water is 0.998 g/mL. If copper pellets were placed in the water would it copper pellets were placed in the water would it
sink or float? (Density of copper is 8.92g/mL)sink or float? (Density of copper is 8.92g/mL)
The copper would sink as its density is higher than that of water.
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Examples:Examples:A sample of aluminum metal has a A sample of aluminum metal has a mass of 8.40g. The volume of the sample is 3.1cmmass of 8.40g. The volume of the sample is 3.1cm33. . Calculate the density of aluminum.Calculate the density of aluminum.
D = m = 8.40g = 2.7g/cm2.7g/cm33
V 3.1cm3
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A sheet of metal has a length of 32.0cm, a width of A sheet of metal has a length of 32.0cm, a width of 2.00cm, and a height of 1.000cm. The density 2.00cm, and a height of 1.000cm. The density of the metal is 9.7g/cmof the metal is 9.7g/cm33. Calculate the mass of . Calculate the mass of
the metal.the metal.
D = m/V m = D x V m = (9.7g/cm3)(32.0cm x 2.00cm x 1.000cm)
m = 620 g620 g
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Specific GravitySpecific Gravity• Comparison of the density of a
substance with the density of a reference substance.
• A hydrometer is used to measure the specific gravity of a liquid.
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TemperatureTemperature• Determines the direction of heat
transfer.
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Temperature ScalesTemperature Scales• Celsius scale: Uses water as the
reference (i.e. 0oC and 100oC)
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Temperature Scales (cont.)Temperature Scales (cont.)• Kelvin scale: Freezing point of water
is 273.15 K and its boiling point is 373.15 K.– Absolute Zero – all motion ceases
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Converting between Celsius Converting between Celsius and Kelvinand Kelvin
K = oC + 273oC = K – 273
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Liquid nitrogen boils at 77.2 K. What is Liquid nitrogen boils at 77.2 K. What is this temperature in degrees Celsius?this temperature in degrees Celsius?
oC = K – 273oC = 77.2 – 273
-195.8-195.8ooCC