Que es la Química, Método Científico

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Chapter 1 Chemistry in Our Lives

1.1 Chemistry and Chemicals

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Publishing as Benjamin Cummings

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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

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Chemicals in Toothpaste

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Learning Check

Which of the following items contain chemicals?

A. Fertilizers

B. Vitamins

C. Happiness

D. Iron nails

E. Paints

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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

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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

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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

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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

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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

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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

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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.

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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)

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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

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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

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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)

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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

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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

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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

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• 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

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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

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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

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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

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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

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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

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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

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1)

vegetable oil 0.91 g/mL

water 1.0 g/mL

Karo syrup 1.4 g/mL

K

W

V

Solution

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Chapter 2 Measurements

2.2

Scientific Notation

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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

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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

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Some Powers of Ten

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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

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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

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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