Que es la Química, Método Científico
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Transcript of Que es la Química, Método Científico
1
Chapter 1 Chemistry in Our Lives
1.1 Chemistry and Chemicals
Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
2
Definition of Chemistry
Science devoted to the study of matter. It is the study of substances in terms of
• Composition What is it made of?• Structure How is it put together?• Properties What characteristics does it
have?• Reactions How does it behave with
other substances?
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Chemistry
Chemistry happens when• A car is started• Tarnish is removed from silver• Fertilizer is added to help
plants grow• Food is digested• Electricity is produced from
burning natural gas• Rust is formed on iron nails
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
Chemistry and sustainable development
Degradable plastics
Organic fertilizers
Solar energy Solar cars Clean industry Insulators
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Chemicals
Chemicals are substances used or produced by a chemical process.
• Soaps• Toothpaste• Polishes• Salt • Hairspray• Vitamins
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
6
Chemicals in Toothpaste
Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings
7
Learning Check
Which of the following items contain chemicals?
A. Fertilizers
B. Vitamins
C. Happiness
D. Iron nails
E. Paints
8
Solution
Which of the following items contain chemicals?
A. Fertilizers contain chemicals
B. Vitamins contain chemicals
C. Happiness does not contain chemicals
D. Iron nails contain chemicals
E. Paints contain chemicals
Substance
Substance- chemical that consists of one type of matter and always has the same composition and properties
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Chapter 1 Chemistry in Our Lives
1.2
Scientific Method: process used by
scientists to explain
observations in nature. Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
11
The scientific method involves: Observations• Facts obtained by observing and measuring
events in nature.
Hypothesis• A statement that explains the observations.
(educated guess)
Experiments• Procedures that test the hypothesis.
Theory • A model that describes how the observations
occur using experimental results.
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Summary of the Scientific Method
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
13
Everyday Scientific Thinking
Observation: The sound from a CD in a CD player skips.
Hypothesis 1: The CD player is faulty.
Experiment 1: When I replace the CD with another one, the sound from this second CD is OK.
Hypothesis 2: The original CD has a defect.
Experiment 2: When I play the CD in another player, the sound still skips.
Theory: My experimental results indicate the original CD has a defect.
Scientific method State the problem (like a question) Hypothesis (suggest an answer to a problem) (If _ind var___ then _dep var___) Plan experiment Gather data Interpret data (look for patterns or trends) Conclusion, plan future work Publish results
Experiment
Way of testing a hypothesis Has an independent and a dependent variable Independent variable- you define it, causes a
change in another Dependent variable- changes in response to the
ind. Var. Control group - reference to find out if there
were any changes in the experimental groups. It has all the same elements except the Ind. Var
Tránsito de San Pedro wants to establish if the installation of radars will affect the average velocity of cars driving through Morones Prieto.
establish the problem (Will radars affect the velocity of cars?)
Present the hypothesis (If there are radars in specific locations then cars will decrease their speed)
Design the experiment (install radars in locations and measure speed with and without radars)
identify independent (radars in specific locations) dependent variable (speed of cars) state the control group. (locations without radars)
Carol is a soccer player. She told Mark that Adidas training shoes have a greater performance than Nike training shoes, in the soccer field.
a) establish the problemb) Present the hypothesisc) Design the experimentd) identify dependent and independent variable e) state the control group.
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Learning Check
The step of scientific method indicated in each is
1) observation 2) hypothesis
3) experiment 4) theory
A. A blender does not work when plugged in.
B. The blender motor is broken.
C. The plug has malfunctioned.
D. The blender does not work when plugged into a different outlet.
E. The blender needs repair.
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Solution
The step of scientific method indicated in each is
1) observation 2) hypothesis
3) experiment 4) theory
A. (1) A blender does not work when plugged in.
B. (2) The blender motor is broken.
C. (2) The plug has malfunctioned.
D. (3) The blender does not work when plugged
into a different outlet.
E. (4) The blender needs repair. Cw-Do from page 9 problems: 1.12-1.14
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Chapter 2 Measurements
2.1
Units of Measurement
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
21
Measurement
You make a measurement
every time you• Measure your height. • Read your watch.• Take your temperature.• Weigh a cantaloupe.
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
22
Measurement
In a measurement
• A measuring tool is used to compare some dimension of an object to a standard.
• Of the thickness of the skin fold at the waist, calipers are used.
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
23
Stating a Measurement
In a measurement, a number is followed by a unit.
Observe the following examples of measurements:
Number Unit
35 m
0.25 L
225 kg
3.4 hr
24
The Metric System (SI)
The metric system or SI (international system) is
• A decimal system based on 10.
• Used in most of the world.
• Used everywhere by scientists.
25
Units in the Metric System
In the metric (SI) system, one unit is used for each
type of measurement:
Measurement Metric SI
length 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)
30
For each of the following, indicate whether the unit describes 1) length, 2) mass, or 3) volume.
____ A. A bag of onions has a mass of 2.6 kg.
____ B. A person is 2.0 m tall.
____ C. A medication contains 0.50 g aspirin.
____ D. A bottle contains 1.5 L of water.
Learning Check
31
For each of the following, indicate whether the unit describes 1) length, 2) mass, or 3) volume.
2 A. A bag of onions has a mass of 2.6 kg.
1 B. A person is 2.0 m tall.
2 C. A medication contains 0.50 g aspirin.
3 D. A bottle contains 1.5 L of water.
Solution
32
Learning Check Identify the measurement with an SI unit. A. John’s height is
1) 1.5 yd 2) 6 ft 3) 2.1 m
B. The race was won in1) 19.6 s 2) 14.2 min 3) 3.5 hr
C. The mass of a lemon is1) 12 oz 2) 0.145 kg 3) 0.6 lb
D. The temperature is1) 85C 2) 255 K 3) 45F
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Solution Identify the measurement with an SI unit. A. John’s height is
3) 2.1 m
B. The race was won in1) 19.6 s
C. The mass of a lemon is2) 0.145 kg
D. The temperature is2) 255 K
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STEP 1 State the given and needed units.
STEP 2 Write a plan to convert the given unit to the
needed unit.
STEP 3 Write equalities/conversion factors that connect the units.
STEP 4 Set up problem with factors to cancel
units and calculate the answer.
Unit 1 x Unit 2 = Unit 2Unit 1
Given Conversion Needed unit factor unit
Guide to Problem Solving (GPS)
35
Setting up a Problem
How many minutes are 2.5 hours?
given unit = 2.5 hr
needed unit = ? min
plan = hr min
Set up problem to cancel units (hr).
given conversion needed unit factor unit
2.5 hr x 60 min = 150 min
1 hr
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
36
A rattlesnake is 2.44 m long. How long is the snake
in centimeters?
1) 2440 cm
2) 244 cm
3) 24.4 cm
Learning Check
37
A rattlesnake is 2.44 m long. How long is thesnake in centimeters?
2) 244 cm
given conversion needed unit factor unit
2.44 m x 100 cm = 244 cm 1 m
Solution
38
• Often, two or more conversion factors are required to obtain the unit needed for the answer.
Unit 1 Unit 2 Unit 3
• Additional conversion factors can be placed in the setup to cancel each preceding unitGiven 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
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How many minutes are in 1.4 days?
Given unit: 1.4 days Needed unit: min
Plan: days hr min
Equalties: 1 day = 24 hr
1 hr = 60 min Set up problem: 1.4 days x 24 hr x 60 min = 2.0 x 103
min
1 day 1 hr
Example: Problem Solving
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• Be sure to check your unit cancellation in the setup.
• The units in the conversion factors must cancel to give the correct unit for the 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 needed unit
Units don’t cancel properly.
Check the Unit Cancellation
More units
Area m2 = m x m Volume m3 = m x m x m Density mass/volume
g/mL or Kg/L
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K = oC + 273 Ex 23 oC = _______ K 135 K = ________ oC
1L = 1 dm3
1 m3 =1000L
Ex 27 m3 = ________ L42
43
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?
1) 2.25 g/cm3
2) 22.5 g/cm3
3) 111 g/cm3
Learning Check
44
Given: mass = 50.0 g volume = 2.22 cm3
Plan: Write the density expression.
D = mass volume
Express mass in grams and volume in cm3
mass = 50.0 g volume = 2.22 cm3
Set up problem using mass and volume.D = 50.0 g = 22.522522 g/cm3
2.22 cm3
= 22.5 g/cm3
Solution
45
Volume by Displacement
• A solid completely submerged in water displaces its own volume of water.
• The volume of the solid is calculated from the volume difference.45.0 mL - 35.5 mL
= 9.5 mL = 9.5 cm3
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
46
Density Using Volume Displacement
The density of the object iscalculated from its mass andvolume. mass = 68.60 g = 7.2 g/cm3
volume 9.5 cm3
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
47
Sink or Float
• Ice floats in water because the density of ice is less than the density of water.
• Aluminum sinks because its density is greater than the density of water.
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
48
Which diagram correctly represents the liquid layers in the cylinder? Karo (K) syrup (1.4 g/mL), vegetable (V) oil (0.91 g/mL,) water (W) (1.0 g/mL)
1 2 3
K
K
W
W
W
V
V
V
K
Learning Check
49
1)
vegetable oil 0.91 g/mL
water 1.0 g/mL
Karo syrup 1.4 g/mL
K
W
V
Solution
50
Chapter 2 Measurements
2.2
Scientific Notation
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
51
Scientific NotationScientific notation • Is used to write very large
or very small numbers.• For the width of a human
hair of 0.000 008 m is written as
8 x 10-6 m• For a large number such
as 2 500 000 s is written as
2.5 x 106 s Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
52
Scientific Notation
• A number written in scientific notation contains a coefficient and a power of 10.
coefficient power of ten coefficient power of ten
1.5 x 102 7.35 x 10-4
• To write a number in scientific notation, the decimal point is moved after the first digit.
• The spaces moved are shown as a power of ten.
52 000. = 5.2 x 104 0.00378 = 3.78 x 10-
3
4 spaces left 3 spaces right
53
Some Powers of Ten
Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings
54
Comparing Numbers in Standard and Scientific Notation
Number in Standard Format Scientific NotationDiameter of the Earth 12 800 000 m 1.28 x 107 mMass of a human 68 kg 6.8 x 101 kgMass of a hummingbird 0.002 kg 2 x 10-3 kg Length of a pox virus 0.000 000 3 cm 3 x 10-7 cm
55
Learning Check
Select the correct scientific notation for each.
A. 0.000 008
1) 8 x 106 2) 8 x 10-6 3) 0.8 x 10-5
B. 72 000
1) 7.2 x 104 2) 72 x 103 3) 7.2 x 10-4
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Solution
Select the correct scientific notation for each.
A. 0.000 008
2) 8 x 10-6
B. 72 000
1) 7.2 x 104
57
Learning Check
Write each as a standard number.
A. 2.0 x 10-2
1) 200 2) 0.0020 3) 0.020
B. 1.8 x 105
1) 180 000 2) 0.000 018 3) 18 000
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Solution
Write each as a standard number.
A. 2.0 x 10-2
3) 0.020
B. 1.8 x 105
1) 180 000