Chapter 2 Scientific Measurements 1 Vanessa N. Prasad-Permaul CHM 1025 Valencia Community College.
1 CH 3: The Metric System Renee Y. Becker CHM 1025 Valencia Community College.
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Transcript of 1 CH 3: The Metric System Renee Y. Becker CHM 1025 Valencia Community College.
1
CH 3: The Metric System
Renee Y. BeckerCHM 1025
Valencia Community College
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The Metric System
• The English system was used primarily in the British Empire and wasn’t very standardized.
• The French organized a committee to devise a universal measuring system.
• After about 10 years, the committee designed and agreed on the metric system.
• The metric system offers simplicity with a single base unit for each measurement.
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Metric System Basic Units
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SI unit
• SI units– In 1960 International System of Units (SI) adopted
– This system has 7 SI base units that all other units can be derived from
– Metric system is a decimal system• We use SI prefixes• Indicates a power of 10
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Measurement and Units
Physical Quantity Name of Unit Abbreviation Mass kilogram kg
Length meter m Temperature kelvin K
Amount of substance mole mol Time second s
Electric current ampere A Luminous intensity candela cd
SI Units
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Metric Prefixes
Unit Symbol Value
meter m 1
decimeter dm 10 = 1 x 101
centimeter cm 100 = 1 x 102
millimeter mm 1000= 1 x 103
micrometer m 1 x 106
nanometer nm 1 x 109
picometer pm 1 x 1012
1 kilometer = 1 x103 meter1 km = 1000 m
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Measurements and Units
• Dimensional-Analysis method uses a conversion factor to express the relationship between units.
Original quantity x conversion factor = equivalent quantity
Example: express 2.50 kg lb.Conversion factor: 1.00 kg = 2.205 lb
2.50 kg x 2.205 lb = 6.00 lb 1.00 kg
Always start with the original quantityThen multiply by the conversion factor
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Measurements and Units
• Remember that anything divided by itself =1
• This is how we can get rid of units!!! They cancel out!!
• So remember when setting up dimensional analysis to always divide the units you are trying to get rid of. And multiply by the unit you want to keep!
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Example 1
• What unit will the answer have for the following?
12 bird x 3 dog x 12 cat = 108 4 bird 1 dog
13 g CO2 x 1 mole CO2 = .30
44 g CO2
56 clowns x 2 doctors x 10 doctors = 3 x 101
12 clowns 3 cops
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Example 2: Metric Conversion
a) 1.267 km m cm
b) .784 L mL
c) 3.67 x 105 cm mm
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Example 3: English Conversion
a) 79 oz lb.
b) 9.63 x 10-3 ft in
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Example 4: Metric-English Conversion
a) 1.34 x 1012 in cm
b) 4.67 x 10-7 lb g
c) 10.5 gal L
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Example 5: Measurement with Compound Units
I am traveling 32 mi/hr, how fast am I traveling in km/hr?
1 mi = 1.61 km
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Volume by Calculations
V = L x w x hLength, width, and height have to be in the same
unit
Example: a box has L = 12 cm, w = 42 cm, h = 32 cm• What is the volume of the box?
V = L x w x h = 12 cm x 42 cm x 32 cm = 1.6 x 104 cm3
– don’t forget to multiply the units as well as the #’s!!!
– If the units are not the same you will have to convert so that they are!!
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Volumes of Solids, Liquids, Gases
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Volume by Displacement
• How we can find density in the lab!!
• If the jade has a mass of 21.3 g what is the density?
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Gas Volume by Displacement
You want to measure the volume of gas given off in a chemical reaction.
The gas produced displaces the water in the flask into the beaker. The volume of water displaced is equal to the volume of gas.
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Density
• The density of an object is a measure of its concentration of mass.
• Density is defined as the mass of an object divided by the volume of the object.
• Density = Mass/Volume
• M = DxV
• V = M/D
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Density
• Density is expressed in different units. It is usually grams per milliliter (g/mL) for liquids, grams per cubic centimeter (g/cm3) for solids, and grams per liter (g/L) for gases.
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Density
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Density
• We can estimate the density of a substance by comparing it to another object.
• A solid object will float on top a liquid with a higher density.
• Object S1 has a density less than that of water, but larger than that of L1.
• Object S2 has a density less than that of L2, but larger than that of water.
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Example 6: Density
• What is the density(in g/mL) of unknown substance that has a volume of 20 mL and a mass of 10 g?
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Example 7: Density
• What is the density (in g/cm3) of a platinum nugget that has a mass of 224.50 g and a volume of 10.0 cm3 ?
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Example 8: Volume
• What is the volume (in mL) of an unknown substance if it’s mass is 0.125 g and it’s density is 1.873 g/mL?
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Example 9: Mass
• What is the mass (in g) of an unknown substance if it’s density is 2.578 g/mL and it’s volume is 4.23 mL?
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Temperature
• Temperature is a measure of the average kinetic energy of the individual particles in a sample.
• There are three temperature scales:
– Celsius
– Fahrenheit
– Kelvin
• Kelvin is the absolute temperature scale.
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Temperature Conversions:
The Kelvin and Celsius degree
are essentially
the same because both
are one hundredth of the
interval between freezing
and boiling points of water.
Temperature
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Temperature
• Temperature Conversions:
– Celsius (°C) — Kelvin temperature conversion:
Kelvin (K) = °C + 273.15
– Fahrenheit (°F) — Celsius temperature conversions:
C = 5/9 (F -32) F = (9/5 * C) + 32
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Example 10: Temperature
Carry out the indicated temperature conversions:
(a) –78°C = ? K
(b) 158°C = ? °F
(c) 375 K = ? °C
(d) 98.6°F = ? °C
(e) 98.6°F = ? K
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Temperature Scales
• On the Fahrenheit scale, water freezes at 32 °F and boils at 212 °F.
• On the Celsius scale, water freezes at 0 °C and boils at 100 °C. These are the reference points for the Celsius scale.
• Water freezes at 273K and boils at 373K on the Kelvin scale.
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Heat
• Heat is the flow of energy from an object of higher temperature to an object of lower temperature.
• Heat measures the total energy of a system.
• Temperature measures the average energy of particles in a system.
• Heat is often expressed in terms of joules (J) or calories (cal).
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Heat vs. Temperature
• Although both beakers below have the same temperature (100 ºC), the beaker on the right has twice the amount of heat, because it has twice the amount of water.