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The World of Chemistry

Chapter 1

Copyright © Houghton Mifflin Company. All rights reserved. 1 | 2

What Do Chemists Do?

• Solve Problems• Devise experiments • Analyze data• Draw conclusions• Develop products


1.1. What Do Chemists Do?


The Chemist’s Shorthand

• Matter:• Atoms:• Elements:• Molecules:• Compounds:

• Composition:

Chemistry is concerned with the systematic study of the matter of universeanything that has a mass and occupied space

the smallest identifying unit of an element

matter containing only one kind of atom element

two or more atoms bonded together

matter that contains different elements chemically bonded together

the relative proportions of the elements in a compound



• Matter:• Atoms:• Elements:• Molecules:• Compounds:

• Composition:

Chemistry is concerned with the systematic study of the matter of universeanything that has a mass and occupied space

the smallest identifying unit of an element

matter containing only one kind of atom element

two or more atoms bonded together

matter that contains different elements chemically bonded together

the relative proportions of the elements in a compound



compound

element



Pure substances

sucrose soln salt in sand



• Physical property: mp, bp, odor, color, etc• Physical change: change of physical properties

without changing chem. comp.• Chemical property : chemical reaction, combustion

• Chemical change: change in chemical comp.• Homogeneous mixture• Heterogeneous mixture

How can we tell the difference between the two substances ?


Mixtures

• Homogeneous (solutions) vs. heterogeneous• homogeneous : uniform in composition• heterogeneous : Non-uniform in composition

• Separation by:• filtration : separating a heterogeneous solid-liquid

mixture• distillation : resolving a homogeneous solid-liquid

mixture


The Scientific Method

Process of Science: asking questions and making careful observations.

science as a means of knowing;raising questions, designing experiments, gathering data, interpreting the data, drawing conclusions, raising more questions

: the structured way of knowing


1.4. Units and Measurement


Mass vs. weight

• Mass: a measure of the amount of matter

• Weight: a measure of downward force given by g.


Prefixes


Temperature Scales

Fahrenheit (German, 1714)Celsius (Swedish, 1742)


Temperature Conversions

• KelvinTK = TC + 273

• CelsiusTC = (TF – 32)/1.8

• FahrenheitTF = 1.8(TC) + 32


Sample Problem

The average human body temperature is 98.6o F. Express this temperature using the Celsius and Kelvin scales.

• TC = (TF – 32)/1.8TC = (98.6 – 32)/1.8 = 37.0o C

• TK = TC + 273TK = 37.0 + 273 = 310 K


Derived Units


Cubic meter, cubic centimeter

3


Intensive & Extensive Properties

depends on how much quantity


Density

massdensity = volume

Density reports the mass of a substance that is present in a given volume of the substance.


Sample Problem

What is the density of a metal that has a mass of 61.5 g and a volume of 8.56 cm3?

=

=

3

3

massdensity = volume61.5 g

8.56 cm7.18 g/cm


Conversion Factors

• One step conversions : a ratio, numerically equal to 1, by which

• a quantity can be converted from one set of units to another

• Multiple conversion factors


1.5. Conversions and Dimensional Analysis

( ) =

39 lb 1 kg3 suitcases 53 kg1 suitcase 2.205 lb

• Use conversion factors to cancel unitsuntil the proper unit is in place.

• Three suitcases weigh 39 lbs each. How many kilograms is this?


( ) =

4qt 0.946 L 1000 mL1 gal 3784 mL1 gal 1 qt 1 L

Sample Problem

How many milliliters are there in onegallon of soda?


1.6. Uncertainty, Precision, Accuracy

• All measurements are made with some degree of uncertainty. To express uncertainty: 151±1 g.

• Exact numbers:a. Defined quantities such as a 1meter = 100

centimeters and items that are counted.• Precision:

a. Indicator of how close repeated measurements are to each other

• Accuracy: a. Indicator of how close a measurement is to its true

value


Accuracy and Precision

Accuracy: How close we are to the true value. Precision: How close our measurements are to each other;

how consistent (or reproducible) our measurementsare.


Significant Figures

: specific numbers in a measurement whose values we can trust325K / 3 = 108.33333333Are the endless decimal digits significant ?


Sample Problem

a. 2012b. 0.0061c. 0.0130d. 6.02 x 1023

(four)(two)(three)(three)

How many significant figures are there in each of these numbers?


Significant Figures in Calculations


a. 13.42 – 2.9 =

Sample Problem

10.5

c. 5.5×102/(4.14 – 1.361) =b. (16)(0.0159) = 0.25

2.0×102

Report the answer to the correct number of significant figures.


The Chemical Challenges of the Future

• Frontiers of medicine• New challenges in agriculture• Challenge of pollution• Global warming and pollution• Better materials• New ways to supply energy• Nanotechnology• Understanding life


Career Opportunities in Chemistry

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