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Transcript of Chapt03 Lecture
Christopher G. Hamaker, Illinois State University, Normal IL© 2008, Prentice Hall
Chapter 3The Metric System
INTRODUCTORY CHEMISTRYConcepts & Connections
Fifth Edition by Charles H. Corwin
Chapter 3 2
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.
Chapter 3 3
Metric System Basic Units
Chapter 3 4
Original Metric Unit Definitions• A meter was defined as 1/10,000,000 of the
distance from the North Pole to the equator.
• A kilogram (1000 grams) was equal to the mass of a cube of water measuring 0.1 m on each side.
• A liter was set equal to the volume of one kilogram of water at 4 C.
Chapter 3 5
Metric System Advantage• Another advantage of the metric system is that it is
a decimal system.
• It uses prefixes to enlarge or reduce the basic units.
• For example:– A kilometer is 1000 meters.
– A millimeter is 1/1000 of a meter.
Chapter 3 6
Metric System Prefixes
• The following table lists the common prefixes used in the metric system:
Chapter 3 7
Metric Prefixes, continued• For example, the prefix kilo- increases a base unit
by 1000:
–1 kilogram is 1000 grams
• The prefix milli- decreases a base unit by a factor of 1000:
–1 millimeter is 0.001 meters
Chapter 3 8
Metric Symbols• The names of metric units are abbreviated using
symbols. Use the prefix symbol followed by the symbol for the base unit, so:
–nanometer is abbreviated nm
–microgram is abbreviated mg
–deciliter is abbreviated dL
–gigasecond is abbreviated Gs
Chapter 3 9
Metric Equivalents• We can write unit equations for the conversion
between different metric units.
• The prefix kilo- means 1000 basic units, so 1 kilometer is 1000 meters.
• The unit equation is 1 km = 1000 m.
• Similarly, a millimeter is 1/1000 of a meter, so the unit equation is 1 mm = 0.001 m.
Chapter 3 10
Metric Unit Factors• Since 1000 m = 1 km, we can write the following
unit factors for converting between meters and kilometers:
1 km or 1000 m 1000 m 1 km
• Since 1 m = 0.001 mm, we can write the following unit factors.
1 mm or 0.001 m 0.001 m 1 mm
Chapter 3 11
Metric-Metric Conversions• We will use the unit analysis method we learned in
Chapter 2 to do metric-metric conversion problems.
• Remember, there are three steps:– Write down the unit asked for in the answer.
– Write down the given value related to the answer.
– Apply unit factor(s) to convert the given unit to the units desired in the answer.
Chapter 3 12
Metric-Metric Conversion Problem
• What is the mass in grams of a 325 mg aspirin tablet?
• Step 1: We want grams.
• Step 2: We write down the given: 325 mg.
• Step 3: We apply a unit factor (1 mg = 0.001 g) and round to three significant figures.
325 mg × = 0.325 g1 mg
0.001 g
Chapter 3 13
Two Metric-Metric Conversions
• A hospital has 125 deciliters of blood plasma. What is the volume in milliliters?
• Step 1: We want the answer in mL.
• Step 2: We have 125 dL.
• Step 3: We need to first convert dL to L and then convert L to mL:
0.1 L and 0.001 mL1 dL 1 L .
Chapter 3 14
Problem, continued• Apply both unit factors, and round the answer to 3
significant digits.
• Notice that both dL and L units cancel, leaving us with units of mL.
125 dL × = 12,500 mL×1 dL0.1 L 1 mL
0.001 L
Chapter 3 15
Another Example
• The mass of the Earth’s moon is 7.35 × 1022 kg. What is the mass expressed in megagrams, Mg?
• We want Mg; we have 7.35 × 1022 kg.
• Convert kilograms to grams, and then grams to megagrams.
7.35 × 1022 kg × = 5.98 × 1019 Mg×1 kg
1000 g 1 Mg
1000000 g
Chapter 3 16
Metric and English Units• The English system is still very common in the
United States.
• We often have to convert between English and metric units.
Chapter 3 17
Metric-English Conversion
• The length of an American football field, including the end zones, is 120 yards. What is the length in meters?
• Convert 120 yd to meters given that 1 yd = 0.914 m.
120 yd × = 110 m1 yd
0.914 m
Chapter 3 18
English-Metric Conversion
• A half-gallon carton contains 64.0 fl oz of milk. How many milliliters of milk are in a carton?
• We want mL; we have 64.0 fl oz.• Use 1 qt = 32 fl oz, and 1 qt = 946 mL.
64.0 fl oz × = 1,890 mL×32 fl oz
1 qt 946 mL1 qt
Chapter 3 19
Compound Units• Some measurements have a ratio of units.
• For example, the speed limit on many highways is 55 miles per hour. How would you convert this to meters per second?
• Convert one unit at a time using unit factors.– first, miles → meters
– second, hours → seconds
Chapter 3 20
Compound Unit Problem• A motorcycle is traveling at 75 km/hour. What is
the speed in meters per second?
• We have km/h; we want m/s.
• Use 1 km = 1000 m and 1 h = 3600 s.
= 21 m/s×1 km
1000 m 1 hr3600 s
75 kmhr
×
Chapter 3 21
Volume by Calculation
• The volume of an object is calculated by multiplying the length (l) by the width (w) by the thickness (t).
volume = l × w × t
• All three measurements must be in the same units.
• If an object measures 3 cm by 2 cm by 1 cm, the volume is 6 cm3 (cm3 is cubic centimeters).
Chapter 3 22
Cubic Volume and Liquid Volume
• The liter (L) is the basic unit of volume in the metric system.
• One liter is defined as the volume occupied by a cube that is 10 cm on each side.
Chapter 3 23
Cubic & Liquid Volume Units• 1 liter is equal to 1000 cubic centimeters
–10 cm × 10 cm × 10 cm = 1000 cm3
• 1000 cm3 = 1 L = 1000 mL
• Therefore, 1 cm3 = 1 mL.
Chapter 3 24
Cubic-Liquid Volume Conversion• An automobile engine displaces a volume of
498 cm3 in each cylinder. What is the displacement of a cylinder in cubic inches, in3?
• We want in3; we have 498 cm3.
• Use 1 in = 2.54 cm three times.
= 30.4 in3×1 in
2.54 cm ×498 cm3 ×
1 in2.54 cm
1 in2.54 cm
Chapter 3 25
Volume by Displacement• If a solid has an irregular shape, its volume cannot
be determined by measuring its dimensions.
• You can determine its volume indirectly by measuring the amount of water it displaces.
• This technique is called volume by displacement.
• Volume by displacement can also be used to determine the volume of a gas.
Chapter 3 26
Solid Volume by Displacement• You want to measure the volume of an irregularly
shaped piece of jade.• Partially fill a volumetric flask with water and
measure the volume of the water.
• Add the jade, and measure the difference in volume.
• The volume of the jade is 10.5 mL.
Chapter 3 27
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.
Chapter 3 28
The Density Concept
• 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.
= densityvolumemass
Chapter 3 29
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.
Chapter 3 30
Densities of Common Substances
Chapter 3 31
Estimating 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.
Chapter 3 32
Calculating Density• What is the density of a platinum nugget that has a
mass of 224.50 g and a volume of 10.0 cm3 ?
• Recall, density is mass/volume.
= 22.5 g/cm3
10.0 cm3
224.50 g
Chapter 3 33
Density as a Unit Factor• We can use density as a unit factor for conversions
between mass and volume.
• An automobile battery contains 1275 mL of acid. If the density of battery acid is 1.84 g/mL, how many grams of acid are in an automobile battery?
• We have 1275 mL; we want grams:
1275 mL × = 2350 gmL
1.84 g
Chapter 3 34
Critical Thinking: Gasoline
• The density of gasoline is 730 g/L at 0 ºC (32 ºF) and 713 g/L at 25 ºC (77 ºF). What is the mass difference of 1.00 gallon of gasoline at these two temperatures (1 gal = 3.784L)?
• The difference is about 60 grams (about 2 %).
= 2760 g×At 0 ºC: 1.00 gal ×730 g
L3.784 L1 gal
= 2700 g×At 25 ºC: 1.00 gal ×713 g
L3.784 L1 gal
Chapter 3 35
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.
Chapter 3 36
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.
Chapter 3 37
• This is the equation for converting °C to °F.
• This is the equation for converting °F to °C.
• To convert from °C to K, add 273.
°C + 273 = K
Temperature Conversions
= °F°C ×100°C180°F( )
( )180°F100°C
= °C(°F - 32°F) ×
Chapter 3 38
Fahrenheit-Celsius Conversions
• Body temperature is 98.6 °F. What is body temperature in degrees Celsius? In Kelvin?
K = °C + 273 = 37.0 °C + 273 = 310 K
( )180°F100°C
= 37.0°C(98.6°F - 32°F) ×
Chapter 3 39
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).
Chapter 3 40
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.
Chapter 3 41
Specific Heat
• The specific heat of a substance is the amount of heat required to bring about a change in temperature.
• It is expressed with units of calories per gram per degree Celsius.
• The larger the specific heat, the more heat is required to raise the temperature of the substance.
Chapter 3 42
Chapter Summary
• The basic units in the metric system are grams for mass, liters for volume, and meters for distance.
• The base units are modified using prefixes to reduce or enlarge the base units by factors of 10.
• We can use unit factors to convert between metric units.
• We can convert between metric and English units using unit factors.
Chapter 3 43
Chapter Summary, continued
• Volume is defined as length × width × thickness.
• Volume can also be determined by displacement of water.
• Density is mass divided by volume.
Chapter 3 44
Chapter Summary, continued• Temperature is a measure of the average energy of
the particles in a sample.
• Heat is a measure of the total energy of a substance.
• Specific heat is a measure of how much heat is required to raise the temperature of a substance.