Chapter 1 - PRIN - Keys to the Study of Chemistry

8/8/2019 Chapter 1 - PRIN - Keys to the Study of Chemistry

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Keys to the Study of Chemistry

Chapter 1


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Is the study of matter,its properties,

the changes that matter undergoes,

and

the energy associated with these changes.


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Definitions

Matter anything that has mass and volume - the stuff of the

universe: books, planets, trees, professors, students

Composition the types and amounts of simpler substances thatmake up a sample of matter

Properties the characteristics that give each substance a uniqueidentity


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Figure 1.1 The distinction between physical and chemical change.


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Figure 1.2 The physical states of matter.


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Distinguishing Between Physical andChemical Change

PROBLEM: Decide whether each of the following processes is primarily aphysical or a chemical change, and explain briefly:

(a) Frost forms as the temperature drops on a humid winter night.

(b) A cornstalk grows from a seed that is watered and fertilized.

(c) A match ignites to form ash and a mixture of gases.

(d) Perspiration evaporates when you relax after jogging.(e) A silver fork tarnishes slowly in air.

Sample Problem 1.2


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energy due to the position of the object orenergy from a chemical reactionPotential Energy

Kinetic Energy energy due to the motion of the object

Energy is the ability to do work.


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Energy is the ability to do work.Figure 1.3A

less stable

more stable

change in potential energy EQUALS kinetic energy

A gravitational system. The potential energy gained when a

lifted weight is converted to kinetic energy as the weight falls.


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Energy is the ability to do work. Figure 1.3B

less stable

more stable


A system of two balls attached by a spring. The potential energygained by a stretched spring is converted to kinetic energy when themoving balls are released.


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Energy is the ability to do work. Figure 1.3C

less stable

more stable


A system of oppositely charged particles. The potential energy gainedwhen the charges are separated is converted to kinetic energy as theattraction pulls these charges together.


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Energy is the ability to do work. Figure 1.3D

less stable

more stable


A system of fuel and exhaust. A fuel is higher in chemical potentialenergy than the exhaust. As the fuel burns, some of its potential energy isconverted to the kinetic energy of the moving car.


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Scientific Approach: Developing a Model

Observations :

Hypothesis:

Experiment:

Model (Theory):

Further Experiment:


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MEASUREMENTS AND MEASUREMENT UNITS Measurements consist of two parts, a number and a unit or

label such as feet, pounds, or gallons. Measurements are made using measuring devices (e.g.

rulers, balances, graduated cylinders, etc.).

Factor-label method or dimensional analysis usesconversion factors to solve problems. If you traveled 150 miles/hour, how many feet/minute did

you travel?


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A Systematic Approach to Solving Chemistry Problems

Problem statement

Plan

Solution

Check

Comment and Follow-up Problem


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Converting Units of Length

PROBLEM: To wire your stereo equipment, you need 325 centimeters (cm) ofspeaker wire that sells for $0.15/ft. What is the price of the wire?

Sample Problem 1.3


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SCIENTIFIC NOTATION The standard position for the decimal is to the right of the

first nonzero digit in the number M.

SIGNIFICANCE OF THE EXPONENT n A positive n value indicates the number of places to the

right of the standard position that the original decimalposition is located.

A negative n value indicates the number of places to theleft of the standard position that the original decimal

position is located.


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Basic or defined units [e.g. 1 meter (1 m)] are used to calculate derivedunits [e.g. 1 square meter (1 m 2)].

These seven units are known as base units. All other units are knownas derived units and are a combination of these seven base units


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The metric system is a decimal system in which larger and smallerunits are related by factors of 10.


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The Tera 10 12

Great Giga 10 9 Man Mega 10 6

Killed Kilo 103

Hundreds Hecto 10 2

Daily Deca 10 1

except gram/liter/meter 10 0

During Deci 10 -1

Christmas Centi 10 -2

Morning Milli 10-3

My Micro 10 -6

Nice Nano 10 -9

Puppy Pico 10 -12

THE METRIC SYSTEM


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Converting Units of Volume

PROBLEM: Within a cell, proteins are synthesized on particles calledribosomes. Assuming ribosomes are generally spherical, whatis the volume (in dm 3 and L) of a ribosome whose averagediameter is 21.4 nm (V of a sphere = 4/3( r3)?


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MATTER Matter is anything that has mass and occupies space.

MASS Mass is a measurement of the amount of matter in an object. Mass is independent of the location of an object. An object on the earth has the same mass as the same object on the

moon.

WEIGHT Weight is a measurement of the gravitational force acting on an object. Weight depends on the location of an object.

An object weighing 1.0 lb on earth weighs about 0.17 lb on the moon.


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Converting Units of Mass

PROBLEM: International computer communications are often carried by opticalfibers in cables laid along the ocean floor. If one strand of optical

fiber weighs 1.19 x 10 -3 lbs/m, what is the total mass (in kg) of acable made of six strands of optical fiber, each long enough to linkNew York and Paris (8.84 x 10 3 km)?

Sample Problem 1.5


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DENSITY Density is the ratio of the mass of a sample of matter

divided by the volume of the same sample.

or

Density units SI = kg/m 3

liquids in g/mL solids in g/cm 3

gases in g/L


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Temperature Scales

Kelvin (K) - The absolute temperature scale begins atabsolute zero and only has positive values.

Celsius ( oC) - The temperature scale used for scientific work,formally called centigrade, most commonly used scale around theworld; water freezes at 0 oC, and boils at 100 oC.

Fahrenheit ( oF) - Commonly used scale in the U.S. for ourweather reports; water freezes at 32 oF and boils at 212 oF.

Temperature (T) A measure of the relative hotness of anobject.

Heat Energy that flows from an object at higher temperature toone at lower temperature.


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Figure 1.6

The freezing and boiling points of water.


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Converting Fahrenheit to Celsius.

Converting Celsius to Fahrenheit.

Converting Kelvin to Celsius.

Converting Celsius to Kelvin

An extensive property depends on the amount of a

substance e.g. mass, volume, and energy An intensive property is independent on the amount of a

substance e.g. density and temperature

Temperature Interconversions

59

C F 32

95

F C 32

C K 273

K C 273


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PRACTICE: Convert the following temperaturesa) 441.4 F to C

b) 212.9 C to F

c) 926.3 C to K

d) 254.0 K to C

e) 312.5 F to K


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The number of significant figures in a measurement depends

upon the measuring device.

Figure 1.9A


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Rules for Determining Which Digits are Significant

All digits are significant

1. Make sure that the measured quantity has a decimal point.2. Start at the left of the number and move right until you reach the

first nonzero digit.3. Count that digit and every digit to its right as significant.

except zeros that are used only to position the decimal point.


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Determining the Number of Significant Figures

PROBLEM: For each of the following quantities, underline the zeros that aresignificant figures (sf), and determine the number of significantfigures in each quantity. For (d) to (f), express each inexponential notation first.

(b) 0.1044 g(a) 0.0030 L (c) 53,069 mL

(e) 57,600. s(d) 0.00004715 m (f) 0.0000007160 cm 3

Sample Problem 1.8


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Rules for Significant Figures in Answers

1. For addition and subtraction . The answer has thesame number of decimal places as there are in the measurement with the fewest decimal places.


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2. For multiplication and division . The number with theleast certainty limits the certainty of the result.Therefore, the answer contains the same number of significant figures as there are in the measurement

with the fewest significant figures.

Rules for Significant Figures in Answers


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Rules for Rounding Off Numbers1. If the digit removed is more than 5, the preceding numberincreases by 1.

2. If the digit removed is less than 5, the preceding number isunchanged.

3. If the digit removed is 5, the preceding number increasesby 1 if it is odd and remains unchanged if it is even.

If the 5 is followed only by zeros, rule 3 is followed; if the 5 isfollowed by nonzeros, rule 1 is followed:

4. Be sure to carry two or more additional significant figuresthrough a multistep calculation and round off only the final answer.


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Issues Concerning Significant Figures

graduated cylinder < buret pipet

numbers with no uncertainty

be sure to correlate with the problem

Electronic Calculators

Choice of Measuring Device

Exact Numbers


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Significant Figures and Rounding

PROBLEM: Perform the following calculations and round the answer to thecorrect number of significant figures:

7.085 cm

16.3521 cm 2 - 1.448 cm 2(a)

11.55 cm 3

4.80 x10 4 mg x(b)

1 g

1000 mg

Sample Problem 1.9


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Precision and AccuracyErrors in Scientific Measurements

Random Error

In the absence of systematic error, produces values that are higherand lower than the actual value.

Precision -Refers to reproducibility or how close the measurements are to oneanother.

Accuracy -

Refers to how close a measurement is to the actual value.Systematic Error -Values that are either all higher or all lower than the actual value.


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Figure 1.8 Precision and accuracy in the laboratory.

Four students recorded the weight of 25 mL of water.

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Chapter 1 - PRIN - Keys to the Study of Chemistry