Joel Henry Hildebrand.

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Principles of Chemistry

BY

JOEL H. HILDEBRAND, PH.D.

Associate Professor of Chemistry in the
University of California.



(PRELIMINARY EDITION)



Copyright, 1917, by Joel H. Hildebrand



LEDERER, STREET & ZEUS Co., PUBLISHERS,
BERKELEY, CALIFORNIA.

1917




CONTENTS

CHAPTER I.

Page

KINDS OF MATTER 7

The Domain of Chemistry Properties Used to Recognize Substances
Heterogeneous Mixtures Solutions Compounds and Elements Sym-
bols Classification of Elements.

CHAPTER II.

THE GAS LAWS AND THE KINETIC THEORY 15

Kinetic Theory Relation between Quantity and Pressure Relation be-
tween Pressure and Volume Relation between Pressure and Concentration
Relation between Pressure, Mass and Speed of the Molecules Effect
of Temperature Absolute Zero of Temperature Effect of changing both
Temperature and Pressure Partial Pressure of different Gases in Mix-
tures Avogadro's Rule.

CHAPTER III.

WEIGHT RELATIONS IN CHEMICAL REACTIONS. ATOMIC

THEORY 24

Law of Conservation of Mass* Law of Simple Multiple Proportions
Atomic Theory Atoms and Molecules, Formulas Numerical Values
of Atomic Weights Interpretation of Formulas Gram-Atoms and.
Gram-Molecules or Mols Chemical Equations Calculation of Weight
Relations of Atomic Weights* of Formulas.

CHAPTER IV.

VOLUME OF GASES. MOLECULAR WEIGHTS 31

Choice of Formulas and Corresponding Atomic Weights Changes in
Volume or Pressure in Gas Reactions Volume of One Mol of Any
Gas Calculation of Weight of a given Volume or vice-versa Deter-
mination of Relative Weights of a Gas and Air Determination of
Molecular Weight Direct Relation between Volumes of Gases and
Weights of other Substances in Reactions Complete Interpretation
of Chemical Equations Molecular Weights of dissolved Substances.

CHAPTER V.

TYPES OF CHEMICAL COMPOUNDS 39

Relation between Stability of Compounds and Metallic or Non-metallic
Character of their Constituent Elements Oxides and Sulfides Halides
Relation of the Relative Positive and Negative Characters of Elements
to the Reactions of their Compounds, (a) Replacement, (b) Metathesis,
(c) Addition Classification of Compounds Acids Bases Salts
Anhydrides.

CHAPTER VI.

VALENCE. WRITING EQUATIONS n 49

Assignment of Valence Numbers Elements exhibiting more than one
Valence Use of Valence in classifying Compounds Writing Formulas
with the Aid of Valence Writing Equations Oxidation and Reduction.

CHAPTER VII.

CHEMICAL NOMENCLATURE 55

Names of Elements Most positive Element named first Binary Com-
pounds designated by Suffix -ide Cf.nipounds whose positive Element
may show different Valences Oxy-acids and $alts Sulfo-acids and Salts
Complex Halogen Acids ;artd Salts-r-Acid and Basic Salts Partially
Dehydrated Acids and their Salts ;,-'

CHAPTER VIII.

QUANTITATIVE RELATIONS INVOLVING SOLUTIONS OF

KNOWN CONCENTRATION 60

Concentration in Terms of Mols per Liter Titration- Standardizing
Solutions The Equivalent: Normal Concentration Summary Ex-
amples Titration involving other Types of Reaction.

CHAPTER IX.

THERMO-CHEMISTRY 65

The Calorie Experimental Determination of Heats of Reaction
Numerical Representation of Heats of Reaction Effect of the State of
the Reacting Substances Indirect Determination of Heats of React ; on
Fuel Value of Foods.




CHAPTER X. Page

BEHAVIOR OF SUBSTANCES DISSOLVED IN WATER. IONIC

Abnormally great Lowering of the Freezing Point Independent Migra-
tion of Ions in Electrolysis Ions carry definite electric Charges The
Atom of Electricity Properties of dilute aqueous Solutions of Strong
Electrolytes are the Sum of independent Sets of Properties, hence
independent Substances are present Heats of Reaction in dilute
Solution of Strong Electrolytes depend on reacting Ions only Degree
of lonization of strong Electrolytes Weak Acids and Bases are less .
ionized Weak Salts lonization of weak polybasic Acids in Steps-
lonization in other Solvents than Water lonization of fused Salts
lonization of Water.

CHAPTER XI.

THE SPEED OF CHEMICAL REACTIONS 81

Application of the Kinetic Theory Effect of Temperature Effect of
Concentration Numerical Relation between Concentration and Speed
Effect of Stirring and of Contact Surface in Reactions occurring at
the Boundaries between Phases Catalysts Enzymes.

CHAPTER XII. ^

CHEMICAL EQUILIBRIUM. THE EFFECT OF CONCENTRATION.... 87
Reversibility of Chemical Reactions It is possible to have all Sub-
stances involved present together in Chemical Equilibrium Effect on
Equilibrium of changing Concentration Quantitative expression of the
Mass Law Dissociation Constants of Electrolytes Chemical Equations
do not indicate Amounts present at Equilibrium.

CHAPTER XIII. '

CHEMICAL EQUILIBRIUM. PROPERTIES W T HICH MAY AFFECT

CONCENTRATION - : 96

Volatility Solubility lonization of Water lonization of weak Acids,
Bases and Salts Complex Ions, (a) Ammonia, (b) Cyanide, (c) Halide,
(d) Oxalate^ Competition between the foregoing Factors, (a) Hydro-
lysis, (b) The Solution of Hydroxides, (c) of Oxides, (d) of Ampho-
teric Hydroxides, (e) of Sulfides in Hydrogen Ion, (f) .of Amphoteric
Sulfides, (g) of Salts of other weak Acids, (h) by forming weak Salts,
(i) by forming complex Ions, (j) by forming Ions of Amphoteric
Hydroxides, (k) Systematizing the Reactions of a given Ion Miscel-
laneous Transformations.

CHAPTER XIV.

CHEMICAL EQUILIBRIUM. THE EFFECT OF PRESSURE AND

TEMPERATURE

Effect of changing total Pressure Effect of changing Temperature
Simultaneous Consideration of all Factors governing Reactions, (a)
"Contact Process," (b) Synthesis of Ammonia, (c) Synthesis of Nitric
Oxide, (d) ''Cracking" of Petroleum.

CHAPTER XV.

OXIDATION AND REDUCTION -

Writing Equations, (a) The Substances produced, (b) Assignment of
Valence Numbers, (c) Change in Valences, (d) Balancing Valence
Changes, (e) Final Balancing Relative Oxidizing and Reducing Powers
of Substances, (a) Metals and their Ions, (b) Solubility of Metals in
Water, Acids and Alkalis, (c) General Table Oxidizing Power and
Speed of Oxidation Substances acting both as oxidizing and reducing
Agents Solution of Insoluble Sulfides Storage Batteries.

CHAPTER XVI.

THE PERIODIC SYSTEM -136

Forms of Periodic Table Density Melting Point Tensile Strength
Valence Noble and Base Metals Metals and Non-metals Strength of
Acids and Bases Amphoteric Sulfides Stability of Hydrides Compari-
son of Oxides and Hydrides Elements that form Complex Ions-
Resemblance of first member of Group to second of succeeding Group
Radioactive Elements Prediction of unknown Elements.

CHAPTER XVII.

DISPERSED SYSTEMS 146

Brownian Movement Optical Properties of Colloidal Solutions
Absorption Electrical Migration Colloidal Particles Relation between
Charge and Stability, Coagulation Emulsions Jellies Emulsion Col-
loids Protective Colloids Preparation of Colloidal Solutions, (a)
Dispersion Methods, (b) Condensation Methods.



PREFACE.

This book has been written primarily to serve as a reference book
in the course in General Chemistry and Qualitative Analysis in the
University of California. There are, it is true, many excellent texts
in existence, but whenever an instructor uses a text written by someone
else he faces the dilemma that a departure from the order and manner
of presentation of the printed text results in the loss of much of its
value to the student as a reference book, while a close adherence to
it, on the other hand, interferes with the freedom and individuality, and
hence with the enthusiasm and effectiveness of the teacher.

The difficulty is nbt altogether avoided by writing one's own book,
as probably every teacher is tempted to do, for a book tends to end the
period of experimentation upon the class and to substitute therefor year
after year of complacent stereotyped repetition. A wise old master of
the teaching art doubtless had this in mind when he replied to the
question as to why he did not write a text book by saying, "I would
not be such a fool, for then I could not change my mind."

Now there are two facts which seem to the writer to indicate a
way to avoid these difficulties. The first is that the difficulties of the
student are not concerned with the simple matters of fact so much as
with general principles, methods and points of view. It is comparatively
easy for him to learn the properties and uses of substances from any
text-book, lecture or laboratory course, but much harder for him to learn
to write equations, to use them in calculations of weight and volume,
to understand and apply such principles as the Ionic Theory or the Mass
Law. Repetition, thought and practice are required in such cases.

The second of these facts is that writers of text-books have been in
the habit of introducing the general principles in the particular connec-
tions which seem best to them at the time of writing, and it is usually
unsatisfactory to change the order followed by the book. The difficulty
is not so much that the material is not well presented, but rather, that
a topic like the Mass Law, for example, is introduced in a chapter
headed sulfur, and must remain there if the illustrations are to be of
any value, whereas, of course, this principle no more belongs under
sulfur than it does under any other element, and the instructor using
the book may wish to introduce it at some totally different place. On
the other hand, the purely descriptive material could be rearranged almost
ad libitum.

It seems to the author, accordingly, that the ideal text-book would
consist of two volumes, one of General Principles, the other of Descrip-
tive Chemistry, the latter a book of moderate dimensions on the plan
of Roscoe and Schorlemmer's "Treatise on Chemistry" or Abegg and
Auerbach's "Handbuch der anorganischen Chemie." Since, however,
the descriptive material is available in so many existing books, the limit
of the author's present ambition is a presentation of the Principles of
Chemistry in such a way as to allow, in its use, the maximum flexibility
consistent with the subject. It is hoped that the treatment of these
principles in this volume is such that the various chapters and sections
can be used in connection with almost any arrangement of descriptive
material. Furthermore, although a certain logical order has been followed



in the text, the effort has been to make the presentation of each topic
such that considerable departure from the given order might be possible
without loss of intelligibility. As a matter of fact, the order in which
the topics are taken up in our own course does not fully correspond
to that here used. Some parts of a chapter such as that on the Periodic
System, for example, may well be introduced in a course much earlier
than other parts, and the arrangement of paragraph headings throughout
has been made with the end in view of facilitating such rearrangement.

This separate treatment of Principles is, however, not only undertaken
to allow flexibility but also to emphasize the Principles of Chemistry to
a degree that seems justified by the present status of chemical science.
The earlier history of all natural sciences is that of description and
classification, and their adepts were necessarily men of well developed
powers of observation and memory rather than of inference and deduc-
tion. We still start the beginner in the historic way, asking him to
commit to memory facts concerning the elements and their compounds.
With the development of the science, however, there has arisen a con-
siderable body of general principles which can serve as the basis for
deduction, and the profound change in the character of chemical research
during the last generation bears witness to the development of the later
type of scientist, the one who seeks causes, and aims to develop means
for predicting and controlling phenomena. In recognition of this change
elementary texts have been "modernized" by the introduction of chapters
on the Ionic Theory, Phase Rule, Chemical Equilibrium, etc., which are
often intrusions foreign to the rest of the book, and so they never become
part of the usable tools of the student. Although, of course, chemistry
is yet far from being an exacV science, we nevertheless have made far
more progress in this direction than is recognized in the traditional plan
of instruction, and progress in both pure science and industry is becoming
constantly more dependent upon ability to predict new facts by the aid
of general principles rather than upon a knowledge of existing facts.

A remarkable plea for such a change in the teaching of chemistry
is made by the late Professor H. LeChatelier in the preface to his book
"Lemons sur Carbone." The entire preface is worth reading by all teachers
of chemistry. In it he says : 'Tour comprendre la necessite de modifier
profondement les methodes d'enseignment de la chimie, il suffit de com-
parer un cours de chimie et un cours de physique .... Dans Tenseign-
ment de la physique on ne parle que des lois des phenomenes naturels.
En chimie, au contraire, c'est une enumeration indefinie de petits faits
particuliers : Formules de combinaisons, densites, couleurs, action de tel

ou tel corps, recettes de preparation, etc L'enseignement de la

chimie minerale est completement immobile depuis soixante-quinze ans."
He goes on to contrast this orthodox method of presentation of chemistry
with the chapter headings from the work of Lavoisier : "De la combination
du cajorique. De la formation des fluides aeriformes. Nomenclature des
acides. Quantite de chaleur degagee dans les differentes combustions.
De la fermentation putride. Des sels neutres, etc.," all of which deal
with general subjects instead of descriptions of substances. He admits
of course, that it is not yet possible to consider chemistry an exact science
whose presentation can be made solely on the basis of general principles,
but holds, nevertheless, that the progress that has been made in this
direction has been far from recognized in the traditional plan of presen-
tation.

It is not intended, by any means, that this volume should furnish the
entire material for a course in general chemistry. It is designed distinctly



as a reference book rather than a text book. Our own course includes
much of the traditional descriptive material, and besides, for entrance to
the University course we prescribe High School chemistry, which is
usually largely descriptive in nature. Our aim is, however, to develop
principles rather than simply to study elements and compounds descrip-
tively. The laboratory manual for our course has been written with
this end in view by Professor W. C. Bray and Dr. Ludwig Rosenstein.

Considerable thought has been expended in devising the exercises at
the end of each chapter. The material in the text does not consist of
facts to be memorized so much as of tools, to learn to use which requires
a great deal of drill. These exercises constitute, therefore, an important
part of the book.

For whatever merit the book may possess, the author desires to make
very great acknowledgements to his colleagues. Our own course has
been made to a large extent in the weekly conferences of instructors, and
the freedom of criticism always enjoyed in these meetings has had a
very large effect in determining the contents of this volume. Especial
thanks are due for the valuable criticism given by Professor G. N. Lewis,
Professor W. C. Bray, Dr. W. L. Argo and Dr. G. E. Gibson, who were
kind enough to read the manuscript.

JOEL H. HILDEBRAND.

Berkeley, Cal., 1917.



CHAPTER I.
KINDS OF MATTER.

The Domain of Chemistry. Various aspects of the material things
we see about us may attract our attention, such as the uses to which
these things may be put, the beauty of form or color they may possess,
or the materials out of which they are made. It is the last of these that
is the concern of chemistry. Two vases may have nothing in common
from an artistic standpoint, and a vase and a plate may serve entirely
different purposes, and yet, from a chemical point of view, all three may
be identical by reason of the material, porcelain, out of which they are
made. Chemistry does not concern itself with articles or objects, as
typified by such words as chair, pen, bottle, nail, wire, but rather with the
substances or materials out of which these and other objects may be
made, as typified by such words as wood, glass, iron, copper, clay, sugar.
It is the task of the chemist to ascertain all of the qualities or properties
of every kind of matter, so that the vast number of different kinds may
be recognized and distinguished from each other.'

It is also the task of the chemist to determine how these substances
or materials may be obtained, or, w r hen obtained, how they may be
preserved. The materials out of which objects are made often do not
in the free state, and the enormous quantities of it which are used for
making such a multitude of things must be obtained from the various
iron ores, by heating them with coke or charcoal in a blast furnace. It
is of course very important to know how much coke to use with a given
amount of ore, and how much iron should be obtained from the ore,
because the cost of iron is partly determined by these factors. The
chemist, therefore, must be concerned not only with iron, its nature and
properties, but also with the conditions necessary for getting it from its
ores, and the quantities of the materials involved in the process. And
then, finally, he must determine how to prevent loss of iron from rusting.

The housewife, in making biscuits with the aid of baking soda and
sour milk, finds that if too little soda is used the biscuits will not be
"light," whereas if too much soda is used they will be yellow, and the
taste will be impaired. She must therefore know, not only that when
soda and sour 'milk are mixed they give a gas that will make the dough
porous, but also the relative amounts necessary for the best results.

In the processes just referred to it is obvious that new kinds of
matter have been produced. The iron ore and the coke are quite evidently
different stuff from iron. The sour milk loses its sour taste when mixed
with sufficient soda, and a gas is evolved quite different from either of
the previous materials. Any such change, in which the kind of matter is
altered, is called a chemical change, or a chemical reaction. When
iron is drawn into wire, or made into nails, it is still iron, and no chemical
change has taken place, but when it rusts it is no longer iron but a brown
powder of very different nature from iron. When marble is cut into
various shapes it is still marble, whether in the form of a statute, a table
top or a building block, possessing all of the characteristics by which we
recognize it as marble. If, however, we heat it for a while to a high
temperature it changes in appearance, losing weight, becoming the
familiar substance we call quicklime. This again is a chemical reaction,



since a new substance is produced. Another chemical reaction takes
place if we allow water to come in contact with the quicklime. The
color changes from light grey to white, heat is evolved, the mass swells
and falls apart to a powder, or, if water is in excess, forms a paste.
The resulting material is called slaked-lime, a substance with properties
different from those of marble or quicklime.

Often we direct our attention, in dealing with chemical reactions,
not so much to the nature of the substances involved, or to their relative
amounts, as to the energy used up or liberated by the process. When
oil burns it unites with something from the air, as we must infer from
the necessity of an air supply, and forms gaseous products, which ordi-
narily do not attract our attention except for the necessity of providing
for their escape. The most important thing is the energy made available
by the reaction, which we may wish to use for light, heat or power. In
a dry cell zinc is used up and electrical energy is obtained. The question
as to what becomes of the zinc is overshadowed by the question as to
how much electrical energy should "be gotten from a definite amount of
zinc.

We see, then, that chemistry is concerned with substances, and their
properties ; with the changes or reactions whereby other substances are
formed ; with the conditions necessary for bringing about or preventing
these reactions; and .with the relative amounts of matter and energy
involved.

Some hint may be gotten from the illustrations given above of the
immense importance of chemistry to the material welfare of mankind.
Great service has been rendered by those who have applied it to the
satisfaction of human needs. It must not be forgotten, however, that these
needs are mental and spiritual as well as material, and that to enlarge
man's mental horizon is quite as worthy an endeavor as it is to increase
his physical comfort. To seek out and discover Nature's mysteries is
not a pursuit that requires utilitarian justification. The world owes an
incalculable debt to the explorers who have led the way to new fields of
thought and endeavor. It is these men who pave the way not only for
the miner, the railroad builder and the farmer, but, most important of all,
for others who love Nature and whose spirits are enriched by her knowl-
edge. To those having this pioneer spirit chemistry offers wide uncharted
realms, to explore which is among the most fascinating of pursuits.

Properties Used to Recognize Substances. Many substances have
characteristics so marked that there is little likelihood of their being
confused with other substances. The color of copper distinguishes it from
other metals. The elacticity of rubber, the taste of sugar, the odor of
ether, serve to distinguish these substances, even in the absence of other
tests, from those encountered in ordinary life. We constantly apply
such obvious tests as those of color, luster, hardness, odor and taste.
W r e distinguish quite readily between solids, liquids and' gases. Very
often, however, we need to refine our methods of observation, or to iise
less obvious properties for distinguishing substances. Instead of being
content with saying that lead is "heavier" than iron, We find it desirable
to express this "heaviness" or density numerically by determining the
weight of a unit volume, usually the number of grams per cubic centi-
meter. The refractive index if a transparent body can be determined
with great exactness and is a most valuable means of identification.
The coefficient of expansion, the conductivity for heat or electricity, the
boiling point, the melting point, the heat of fusion or of vaporization,

8



are all quantities having characteristic values for individual substances,
and which may be accurately determined by appropriate methods.

The chemical changes which substances may undergo offer important
means of identification. Gold may be indistinguishable from certain
samples of brass in appearance, but nitric acid at once differentiates them
by dissolving the latter. Powdered talc and starch in a face powder
might readily be differentiated by the fact that the latter will swell up
and dissolve in boiling water, or that it will readily burn.

Heterogeneous Mixtures. As we attempt to apply our tests to dis-
tinguish substances, we notice that some materials give a rather ambiguous
answer. What shall we consider to be the color, density or hardness of
a piece of granite? On close ^xamination we find it composed of several
kinds of mineral, having different degrees of hardness, different colors
and different properties in general. . Although we might determine the
density of a given piece of granite it would be folly to talk about the
density of granite in general, because the constituents of granite are
present in different proportion in different samples/^Granite is obviously
a mixture and not a pure substance, and its properties change abruptly
from one small region to another. These regions within which the
properties suffer no abrupt changes, in this case quartz, mica and feldspar,
are called phases. A mixture containing more than one phase is called
a heterogeneous mixture. Another example is muddy water. Here we
cannot see the different phases quite so readily, but a microscope or a
filter shows quite distinctly that two phases are present. Some alloys, like
solder, appear quite uniform to the eye, as if they contained but one phase,
whereas, by careful etching with acid and using a microscope with
reflected light, it is evident that the alloy is heterogeneous, more than


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Online LibraryJoel Henry HildebrandPrinciples of chemistry → online text (page 1 of 19)