what is measurement? units of measurement when do you measure? measure your height. read your...
TRANSCRIPT
What is measurement? Units of
Measurement When do you
Measure?• measure your height. • read your watch.• take your temperature.
• weigh a cantaloupe.
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Measurement in ChemistryIn chemistry we
• measure quantities.• do experiments.• calculate results. • use numbers to report
measurements.• compare results to
standards.• all with needed tools• every measurement,
• number followed by unit
Number and Unit
35 m
0.25 L
225 lb
3.4 hr
The Metric System (SI)
metric system or SI (international system)
• decimal system based on 10.
• Used worldwide.(M)
• Used by scientists (SI).
following unit used for each type of measurement:
Measurement Metric SILength
meter (m) meter (m)Volume
liter (L) cubic meter (m3)Mass
gram (g) kilogram (kg)Time
second (s) second (s)Temperature
Celsius (C) Kelvin (K)
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Length Measurement
Length
• measured using a meter stick.
• Uses unit of meter (m) in both systems.
• unit of an inch equal to exactly 2.54 centimeters in metric (SI) system.
1 in. = 2.54 cm
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Volume Measurement
Volume • space occupied by a
substance. • measured using a
graduated cylinder (liquids)
• metric system• unit liter (L) in• 1 L = 1.057 qt
• SI system (solids)• m3(cubic meter)
Mass Measurement
mass of an object
• quantity of material it contains.
• measured • balance.
• metric system• . gram (g)
• SI system• kilogram (kg)
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Temperature Measurement
temperature of a substance • indicates how hot or cold.• metric system
• Celsius (C)
• SI system • Kelvin (K) scale.
• thermometer here shows• 18ºC or 64ºF.
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Time Measurement
Time measurement
• metric and SI systems.• second(s)
• based on an atomic clock • uses a frequency
emitted by cesium atoms
What are scientific notation?• very large or very small numbers
• coefficient and a power of 10• width human hair is 0.000 008 m
• written 8 x 10-6 m.• large number such as 4 500 000 s
• written 4.5 x 106 s
• Let’s explore more ! coefficient power of ten coefficient
power of ten 1.5 x 102 7.35 x
10-4
decimal point moved after first digit
spaces moved shown as power of ten. 52 000. = 5.2 x 10 4 0.00378 = 3.78 x
10-3
4 spaces left 3 spaces right
Some Powers of Ten
Numbers written in standard format
and in scientific notation.
Diameter of the Earth12 800 000 m
1.28 x 107 m Mass of a human
68 kg 6.8 x 101 kg
Length of a pox virus0.000 03 cm
3 x 10-5 cm10
. l2. . . . l . . . . l3 . . . . l . . . . l4. . cm
• determine a quantity such as height or mass• markings on meter stick end of orange line are read
asfirst digit 2 plus second digit 2.7
• last digit obtained by estimating• length reported as 2.76 cmdigits 2 and 7 are certain
(known).• The final digit 6 was estimated (uncertain).• All three digits (2.76) are significant including
estimated digit.
What are measured numbers ?
. l3. . . . l . . . . l4. . . . l . . . . l5. . cm
• For this measurement• first and second known digits are 4.5.
• line ends on mark• estimated digit in hundredths place 0.
• measurement • reported as 4.50 cm.
Zero as a Measured Number!
What are significant numbers?Significant figures • obtained from
measurement• include all known
digits plus estimated digit.
• reported • measurement depend on
measuring tool.
• non-zero numbers in measured number are significant.
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38.15 cm 45.6 ft 265.6 lb
3122.55 m 5
The two kinds of zeros?
Sandwiched zeros• occur between nonzero
numbers.• are significant.
Number significant digits
50.8 mm 32001 min 4 0.0702 lb 3 0.40505 m 5
Trailing zeros & Leading zeros
• follow non-zero numbers in numbers without decimal points.
• Precede non-zero digits in a decimal number
• are usually place holders. • are not significant.
Number significant digits
25 000 cm 2 200 kg 10.0156 oz 30.0042 lb 225 005 000 g 5
What are prefixes?
A prefixfront of a unit increases or decreases size makes units larger or smaller
one or more factors of 10. indicates a numerical value.
prefix = value1 kilometer = 1000 meters
1 kilogram = 1000 grams
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Metric and SI Prefixes need to know!
An equality
states same measurement in two different units.can be written using
relationships between two metric units.
Example: 1 meter same as 100 cm and 1000 mm.
1 m = 100 cm1 m = 1000 mm
What are metric equalities?
Measuring Length
Several equalities can be written for length metric (SI) system
1 km = 1000 m
1 m = 1000 mm
1 m = 100 cm
1 mm = 0.001 m
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Measuring Volume
Several equalities can bewritten for volume metric(SI) system
1 kl = 1000 l1 l = 1000 ml1 l = 100 cl1 ml = 0.001 l
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Measuring Mass
Several equalities can be
written for mass metric (SI) system
1 kg = 1000 g1 g = 1000 mg1 g = 100 cg
1 mg = 0.001 g
Equalities • use two different units
• Describe same measured amount.
• written for relationships between units of the metric system, U.S. units, or between
For example,
1 m = 1000 mm
1 lb = 16 oz
2.205 lb = 1 kg
Other equalities between metric and U.S. units?
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Some Common Equalities
contents of packaged foods
• U.S. are listed as both metric and U.S. units• Indicate same amount of a substance in two
different units.
A conversion factor • fraction obtained from an equality
Equality: 1 in. = 2.54 cm• written as a ratio with a numerator and
denominator.
• can be inverted to give two conversion factors for every equality. 1 in. and 2.54 cm
2.54 cm 1 in.
Use conversion factors to change between units!
A conversion factor • may be obtained from information in a word
problem.• written for that problem only.
Example 1: The price of one pound (1 lb) of red peppers is
$2.39.1 lb red peppers and $2.39$2.39 1 lb red peppers
Example 2: The cost of one gallon (1 gal) of gas is $2.34.
1 gallon of gas and $2.34$2.34 1 gallon of gas
Conversion Factors in a Problem
A percent factor• Gives ratio of the parts to whole.
% = Parts x 100Whole
• Uses same unit to express percent.• Uses value 100 and unit for whole.• can be written as two factors.
Example: A food contains 30% (by mass) fat.
30 g fat and 100 g food100 g food 30 g fat
Percent as a Conversion Factor
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The thickness of the skin fold at
the waist indicates 11% body
fat. What percent factors can be
written for body fat in kg?
Percent factors using kg:
11 kg fat and 100 kg mass
100 kg mass 11 kg fat
Another example!
To solve a problem• Identify given unit• Identify needed unit.
Example: A person has a height of 2.0 meters. What is that height in inches?
given unit is initial unit of height. given unit = meters (m)
needed unit is unit for answer. needed unit = inches (in.)
Given and Needed Units can be used in problem solving!
Learning Check
An injured person loses 0.30 pints of blood. How
many milliliters of blood would that be?
Identify the given and needed units given in this
problem.
Given unit = _______
Needed unit = _______
1. Write given and needed units.2. Write a unit plan to convert given unit to needed
unit.3. Write equalities and conversion factors to
connect units.4. Use conversion factors to cancel given unit and
provide needed unit.
Unit 1 x Unit 2 = Unit 2
Unit 1Given x Conversion = Needed
unit factor unit
Problem Setup steps!
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How many minutes are 2.5 hours?
Given unit = 2.5 hrNeeded unit = minUnit Plan = hr
min
Setup problem to cancel hours (hr).
Given Conversion Neededunit factor unit2.5 hr x 60 min = 150 min
(2 SF) 1 hr
Setting up a Problem
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A rattlesnake is 2.44 m long. How many centimeters long is the snake?
Given Conversion Neededunit factor unit
2.44 m x 100 cm = 244 cm 1 m
A solved example
• Often, two or more conversion factors are required to obtain unit needed for answer.Unit 1 Unit 2Unit 3
• Additional conversion factors are placed in setup to cancel each preceding unit
Given unit x factor 1 x factor 2 = needed unitUnit 1 x Unit 2 x Unit 3 = Unit 3
Unit 1 Unit 2
Using Two or More Factors
How many minutes are in 1.4 days? Given unit: 1.4 days
Factor 1 Factor 2 Plan: days hr min
Set up problem: 1.4 days x 24 hr x 60 min = 2.0 x 103 min
1 day 1 hr 2 SF Exact Exact = 2 SF
Example: Problem Solving
• check your unit cancellation in setup.• units in conversion factors must cancel to give
correct unit for answer.
What is wrong with the following setup?
1.4 day x 1 day x 1 hr 24 hr 60 min
Units = day2/min is not the unit neededUnits don’t cancel properly.
Remember to check the unit cancellation!
Another example! the GPS
What is 165 lb in kg?STEP 1 Given 165 lb Need
kgSTEP 2 PlanSTEP 3 Equalities/Factors 1 kg = 2.20 lb 2.20 lb and 1 kg
1 kg 2.20 lbSTEP 4 Set Up Problem 165 lb x 1 kg = 75.0
kg 2.20 lb
Given: 4.65 L Needed: gallons
Plan: L qt gallon
Equalities: 1.06 qt = 1 L; 1 gal = 4 qt
Set Up Problem:
4.65 L x x 1.06 qt x 1 gal = 1.23 gal 1 L 4 qt
3 SF 3 SF exact 3 SF
A bucket contains 4.65 L of water. How many gallons of water is that?
3.0 ft x 12 in x 2.54 cm x 10 mm = 1 ft 1 in. 1 cm
Calculator answer: 914.4 mm Needed answer: 910 mm (2 SF rounded)
Check factor setup: Units cancel properlyCheck needed unit: mm
If a ski pole is 3.0 feet in length, how long is the ski pole in mm?
If your pace on a treadmill is 65 meters per minute, how many minutes will it take for you to walk a distance of 7500 feet?
Given: 7500 ft 65 m/min Need: min
Plan: ft in. cm m min
Equalities: 1 ft = 12 in. 1 in. = 2.54 cm 1 m = 100 cm
1 min = 65 m (walking pace)
Set Up Problem:
7500 ft x 12 in. x 2.54 cm x 1m x 1 min 1 ft 1 in. 100 cm 65 m
= 35 min final answer (2 SF)
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Percent Factor in a Problem
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
If the thickness of the skin fold at the waist indicates an 11% body fat, how much fat is in a person with a mass of 86 kg?
percent factor
86 kg mass x 11 kg fat
100 kg mass
= 9.5 kg fat
Another example:
How many lb of sugar are in 120 g of candy if the candy is 25%(by mass) sugar?
percent factor
120 g candy x 1 lb candy x 25 lb sugar
454 g candy 100 lb candy
= 0.066 lb sugar
Density• Compares the mass of an object to its
volume.• Is the mass of a substance divided by its
volume.
Density expressionDensity = mass = g or g = g/cm3 volume mL cm3
Note: 1 mL = 1 cm3
• Ice floats in water • because density of ice is less than density of
water.
• Aluminum sinks • because its density is greater than density of
water
What is density?
Osmium is a very dense metal. What is its density in g/cm3 if 50.0 g of osmium has a volume of 2.22 cm3?
Given: mass = 50.0 g volume = 22.2 cm3
Plan: Place the mass and volume of the osmium metal
in the density expression.
D = mass = 50.0 g volume 2.22 cm3
calculator = 22.522522 g/cm3
final answer (2) = 22.5 g/cm3
Problem on density
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How to determine volume by displacement ?
• solid completely submerged in water displaces its own volume of water.
• volume of solid is calculated from volume difference.45.0 mL - 35.5 mL
= 9.5 mL = 9.5 cm3
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Density Using Volume Displacement
The density of the zinc object is
then calculated from its mass
and volume.
mass = 68.60 g = 7.2 g/cm3 volume 9.5 cm3
What is the density (g/cm3) of 48.0 g of a metal if the level of water in a graduated cylinder rises from 25.0 mL to 33.0 mL after the metal is added?
Find the volume first?
object
33.0 mL 25.0 mL
Solution
Given: 48.0 g Volume of water = 25.0 mL
Volume of water + metal = 33.0 mL
Need: Density (g/mL)Plan: Calculate the volume difference. Change to
cm3, and place in density expression.
33.0 mL - 25.0 mL = 8.0 mL
8.0 mL x 1 cm3 = 8.0 cm3
1 mLSet up Problem:
Density = 48.0 g = 6.0 g = 6.0 g/cm3
8.0 cm3 1 cm3