A course in inorganic chemistry for colleges

Preface

This book is intended for college students who devote a year to general chemistry. It is primarily a students' book, and is not designed to replace the large text-books, which are better suited for reference than for class use. The descriptive portions of the text include the well-established topics usually taught in a year of college chemistry, though considerable space is devoted to the application of modern principles to chemical industries. The theoretical portions include not only the principles whose value was demonstrated long ago, but also many recent conceptions, which are fast becoming indispensable in interpreting chemical and physical phenomena. Some of the theoretical topics, which are distributed through the text at serviceable points, are the theory of electrolytic dissociation, reversible reactions, equilibrium, catalysis, vapor pressure, electrolysis, and the behavior of dissolved substances. It is hoped that the book as a whole will be found adequate for all students whose work is confined to a year and will likewise serve as a broad foundation for those who continue the study of chemistry.

In the preparation of the manuscript and correction of the proof, judicious advice was received from Professor Frank W. Durkee, Tufts College, Tufts College, Mass., Assistant Professor William Poster, Princeton College, Princeton, N.J., Professor Arthur J\ Hopkins, Amherst College, Amherst, Mass., Professor James F. Norris, Simmons College, Boston, Mass., Professor Charlotte F. Roberts, Wellesley College, iv PREFACE

Wellesley, Mass., Professor Benjamin W. Van Riper, Wheaton College, Wheaton, 111., and others. The author is grateful to these teachers for their help, but he assumes entire responsibility for all statements in the book.

L. C. N.

Boston University, Boston, Mass., January, 1909.

Preface To Revised Edition

Opportunity has been taken in this edition to revise the portions dealing with the theory of chemistry. Some topics have been rewritten and several new ones have been introduced. This revision and extension include catalysis, osmotic pressure, hydrolysis, colloidal solutions, mass action, reversible reactions, displacement of equilibrium, solubility product, adsorption, radioactivity, atomic weights, valence, and molecular weights. Many other topics have been improved and extended to conform to the advance of science, especially those dealing with the applications of chemistry to the arts and industries as well as to life itself. Nearly two hundred and fifty new problems and exercises have been inserted. Numerical data have been corrected and the tables have been revised. These extensive modifications, however, have not destroyed the pedagogical features that commended the first edition to such a

large number of college teachers.

L. C. N.

Boston University, Boston, Mass., May, 1916.

Contents

CHAPTER PAGE

L Matter, Energy, and Change. • 1

Properties of Matter — Physical and Chemical Changes

CHAPTER I Physical and Chemical Changes — Matter — Energy — Elements — Compounds

Chemistry is one of the natural sciences. By a natural science we mean an organized group of knowledge devoted primarily to the study of matter and energy. There are several of these groups. Some, like geology, deal for the most part with the concrete aspects of science, while others, like chemistry and physics, are concerned with both abstract and concrete phases. The different groups of natural sciences are not independent. Indeed, they often overlap and have indefinite boundaries. This has always been characteristic of chemistry and physics, and recent study has drawn them even more closely together.

The scope of chemistry is rather difficult to outline, especially at the outset of its study. Hence it is only possible at this stage to present a preliminary and somewhat incomplete conception, leaving to future pages its development, interpretation, and application. Chemistry deals with the properties of matter, with the changes involved in the transformations of different kinds of matter, with numerous laws, theories, and hypotheses summarizing chemical phenomena, and with the manufacture and utilization of a vast number of substances indispensable to mankind.

Properties of Matter. — Different substances are identified by characteristics called properties. Thus, some substances are solid, others liquid, and still others gaseous, though the special physical state of a substance depends usually upon its temperature. For example, water, mercury, and many other substances, which are liquid at the ordinary temperature, become solid if cooled to a low temperature and gaseous if heated to a high temperature. Other familiar properties are color, odor, taste, relative weight, crystalline structure, luster, hardness, melting point, boiling point, and solubility. Many properties are exhibited when substances are subjected to the action of light, electricity, and particularly to a wide range of temperature. But the most important properties are doubtless those exhibited when different substances act upon each other and thereby produce the profound changes characteristic of chemistry.

Let us consider some properties of the substance sulphur. Observation shows it is a solid which has a yellow color, no odor, no taste, and a crystalline structure. It is relatively heavier than water, because it sinks when placed in a vessel of water, but it is insoluble in water. Experiment shows that when sulphur is heated, it melts into a pale yellow liquid, which turns brown at a comparatively low temperature and remains so until the temperature is quite high, whereupon it becomes viscous like tar and finally boils, yielding a yellow smoke which looks much like sulphur. In the light sulphur has luster, i.e. it reflects light. It does not conduct electricity, for when introduced into the circuit of an ordinary electric bell, it prevents the electricity from ringing the bell; on the other hand, when rubbed with a cloth, sulphur becomes electrified and attracts tiny pieces of paper. If a piece of sulphur is heated to a high temperature, it takes fire and burns. The flame is blue, and an invisible, suffocating product is detected by the odor; if burned long enough, all the sulphur is transformed into this gas. Finally, if sulphur and a powdered metal, such as iron or copper, are mixed and heated in a test tube, the mixture begins to glow, the incandescence often spreading throughout the mass even after the test tube has been removed from the flame. The product is neither sulphur nor iron but a black substance having properties quite different from those of the original constituents. Thus, step by step, we have established by observation and experiment those properties which serve to identify sulphur and to distinguish it from all other substances. By a similar though often more elaborate and complicated procedure the properties of all substances can be discovered, recorded, and classified.

Changes in Matter and Classification of Properties. —

Observation and experiment show that substances often change or can be changed. These changes are shown by a change in properties. Sometimes the change merely involves a temporary change in properties. Thus, water can be changed into steam or ice, and iron can be magnetized or melted, but the water and iron are not thereby fundamentally altered. Apparently they are changed into new substances, but they are not essentially changed, for, although some of the properties are new, rigid examination shows that no new substances have been formed. The steam, ice, magnetized iron, and melted iron are still the substances chemically known as water and iron. Indeed, it is only necessary to cool the steam and the melted iron and to melt the ice to obtain the original substances, which are familiar as water and iron. Changes which do not involve the transformation of substances into new substances are physical changes. In physical changes the change in a substance is often only temporary and is due to some change in or departure from the conditions which usually prevail, e.g. a change in temperature, pressure, or electrical conditions, and as soon as these new conditions are removed the substance regains its familiar properties. Thus, when iodine is heated in a test tube, the solid iodine turns into a beautiful violet vapor which solidifies in the colder part of the test tube, where it may be recognized as iodine by its steel-gray color and crystalline form. The iodine has not been transformed into a new substance, but is merely changed physically, assuming for the time being properties characteristic of iodine at a higher temperature than the ordinary.

Very often, however, substances are changed fundamentally, their essential nature is affected, and the change is manifested by the formation of new substances. The original substance with its properties disappears, often completely, and one or more new substances with characteristic properties appear. Thus, coal is readily changed into ash and an invisible gas which have properties totally unlike those of coal. The change is permanent, too, for the ash and gas are new substances and do not become coal again as soon as they are cold. Changes which involve the transformation of substances into new substances are chemical changes.

An examination of the properties of sulphur recorded above reveals two classes which are more or less distinct. Color, odor, taste, relative weight, crystalline structure, luster, and electrical behavior are exhibited by unchanged or unchanging sulphur. They are associated with physical changes, and their manifestation does not involve a disappearance of the substance nor its transformation into another substance. Thus, sulphur is readily recognized as sulphur during its immersion in water or its electrification by rubbing. Properties exhibited during physical changes or by an unchanging substance are called physical properties. On the other hand, certain properties — not always readily detected — are exhibited only by chemical changes. Their manifestation involves a fundamental change in the nature of substances. Thus, sulphur burns in air and unites chemically with iron, thereby forming new substances; oxygen, as we shall see later, readily undergoes chemical transformation, uniting with many substances; furthermore, many substances are decomposed into other substances by heat or electricity. Those properties — not essentially physical — manifested by substances when they undergo chemical changes are called chemical properties.

It is clear from the foregoing paragraphs that typical physical changes are characterized by the alteration of physical properties, while chemical changes are characterized by the formation of one or more new substances. Examples of familiar physical changes are changes in physical state (illustrated by the formation of ice and vapor from water, and vice versa), production of the colors in the sky, magnetization of iron, and electrification of glass. Familiar chemical changes are the rusting of iron, burning of oil in a lamp, digestion of food, souring of milk, and combustion of wood.

It is not always possible to separate physical and chemical properties into two sharply defined classes nor to call certain changes entirely physical or exclusively chemical. Some chemists advocate the adoption of a third class of changes, viz. physico-chemical changes, such as fusion {i.e. melting) and solution. Thus, when sulphur is boiled or dissolved in some liquid, properties are exhibited which are in part physical and in part chemical. For example, if boiled sulphur is poured while still hot and thick into water, the product is a brown, plastic, gummy mass totally unlike the original sulphur in appearance though it reverts to ordinary, yellow sulphur in time; similarly, powdered sulphur disappears {i.e. dissolves) in the liquid carbon disulphide, and is apparently converted into another substance, though it can be readily recovered, often as beautiful yellow crystals, by evaporating the liquid. Many substances besides sulphur when fused {i.e. melted) or dissolved exhibit properties which do not readily fall into either of the classes mentioned above. Such properties are often called physico-chemical properties.

Chemical Action. — When emphasis is laid upon the chemical change, the participating substances or reagents are said to undergo chemical action, to interact, or to react. This mutual or reciprocal action is called a chemical reaction. Usage of these terms is not uniform, but they are used in this book in the sense just stated. Thus, when copper is put into dilute nitric acid, the evidence of physical change in the acid is the rise in temperature, but this is quite subordinate to the evidence of chemical change, viz. the gradual disappearance of the copper, the liberation of a brown gas, and the production of a new substance which dissolves readily in the acid and colors it blue. Further experiment confirms these observations, for when some of the blue acid solution is evaporated, a blue solid is left which dissolves in water, gives off the brown gas when heated, and also forms a solution which deposits copper upon an iron nail. Chemical action has clearly taken place and the whole phenomenon was a chemical reaction.

Reactions are often complicated, but extensive study has shown that there are four general kinds, — combination, decomposition, substitution, and double decomposition. These will be illustrated and discussed in appropriate places.

Matter and Energy. — All changes studied in chemistry involve matter and energy.

It is sufficiently accurate for our present purpose to define matter as substance revealed to our senses by properties, the fundamental property being weight. In chemical changes matter is transformed ; that is, substances are so changed that new substances are formed. Such changes, as we have already learned, involve a substitution of new properties for old ones. One property of substances, however, is not changed, viz. the weight. Careful and extensive study shows that the total weight of the substances participating in a chemical change is apparently unaltered. This means that the sum of the weights of the substances which enter into a chemical change equals the sum of the weights of the new substances resulting from the chemical change. This feature of chemical change is sometimes briefly summed up by saying, " matter is indestructible." This rather comprehensive statement is one form of a law called the Law of the Conservation of Matter. It is preferably stated thus: —

No weight is lost or gained in a chemical change.

Observation shows that work is done by motion, heat, light, and electricity. Thus, at Niagara Falls the water turns wheels which are connected with dynamos, and the electricity generated thereby is used to operate street cars, furnish light, and produce the heat which is used in certain chemical industries. The term energy is applied to whatever produces work or can be converted into work. For example, motion, heat, light, and electricity are familiar forms of energy, and are usually studied in physics. In chemistry we study these forms and also another form, called chemical energy. Energy, like 'matter, is transformable, yet apparently constant in amount. Observation of the actual transformations of the different forms of energy is an everyday experience. Coal in burning gives up its chemical energy in the form of heat, and the heat becomes motion. In an electric battery chemical energy is changed into electricity, which in turn becomes motion in a bell, or heat in a cooking utensil, or light in a metal wire, or even chemical energy in an electroplating apparatus. All chemical changes involve a transformation of energy. The chemical energy is locked up, so to speak, in substances, and when chemical changes occur there is a transformation and redistribution of energy. Thus, the heat which is often needed to start chemical changes really becomes transformed, in part at least, into chemical energy, while the heat produced by chemical changes is the result of the transformation of some of the chemical energy into heat. So also the light which is essential in photography is transformed into chemical energy and locked up as such in the chemicals on the photographic plate. Food contains chemical energy, and when food is digesting, this energy is being transformed into heat, which maintains the temperature of the body. But all these transformations involve no loss or gain in the total amount of energy involved. When a known amount of heat is put into a substance and stored up as chemical energy, as it were, that heat can be recovered as heat or as an equivalent amount of some other form of energy. The amount of chemical energy is always altered in chemical changes, but the total amount of energy involved is unchanged. The characteristics of energy are often summarized in a brief statement called the Law of the Conservation of Energy, thus : —

Energy can be transformed without loss, but cannot be (by any known means) created or destroyed.

Chemical Elements and Chemical Compounds. — In chemistry we study almost exclusively two classes of substances, viz. elements and compounds. Mixtures, especially the kind of mixture known as a solution, receive some attention. Chemical compounds consist of chemical elements united with one another. There are thousands of compounds, but only about eighty elements.

Chemical Elements. — An extensive examination of many different kinds of matter has shown that certain kinds can be decomposed at will into two or more substances totally unlike the original matter, but that other kinds are not reducible by any means at present under our control. Water, for example, can be decomposed into the gases, hydrogen and oxygen, which are entirely different from water. But neither hydrogen or oxygen can be decomposed by any known process. Furthermore, oxygen and hydrogen cannot be transformed into each other by any known process. Other substances can be added chemically to oxygen or hydrogen, but nothing can be taken away from them chemically, nor can anything be produced from them without increasing their weight. When oxygen or hydrogen undergoes chemical change, there is addition, an increase in weight, a transformation into a new substance having new properties, and especially a greater weight than the original amount of oxygen or hydrogen; these chemical changes are never accompanied by loss in weight. Furthermore, oxygen and hydrogen have characteristic properties; some are much alike, while others are totally different. Oxygen and hydrogen are elements, and all other kinds of matter which have fundamental characteristics typified by oxygen and hydrogen are likewise elements. The essential properties of the chemical elements will be set forth as we proceed with our study of the elements and their compounds. It has been customary for many years to regard elements as those substances which cannot be decomposed into simpler substances or transformed without loss of weight. It would follow from this traditional definition that the elements are the primary forms of matter, so to speak, and are chiefly characterized by stability. This is true of most elements, as far as we know. But our inability to decompose elements does not necessarily mean that they are immutable under all conditions. Indeed, their instability is shown by the spontaneous decomposition of certain elements, especially radium. Nevertheless, it is sufficient for our present purpose to regard the chemical elements as the fundamental materials from which compounds are formed and to which compounds are finally reduced. Questions concerning transmutation can be postponed until more facts are available.

Each element is designated by a symbol, which is an abbreviation of its name. The following is an alphabetical

Table of Important Elements and their Symbols

Name

Name

Al

Lead .

Pb

Sb

Li

As

Magnesium . . . . .

Mg

Ba

Mn

Bi

Hg

B

Ni

Br

N

Cd

Calcium . . . . . .

Ca

P

C

Pt

CI

K

Cr

Silicon ......

Si

Cobalt .

Co

Silver .

Ag

Cu

Na

F

Strontium . . . . .

Sr

Gold

Au

S

H

Tin

Sn

I

Zinc

Zn

Iron

Fe

The elements are not uniformly distributed in nature, either in abundance or mode of occurrence. Our knowledge of the relative abundance of the elements is based on a study of the atmosphere, the ocean, and a shell of the earth's crust about ten miles deep. The approximate distribution of matter in these three portions of the globe is seen in the following

Table of the Distribution of Matter

Atmosphere 03 per cent

Ocean 7.08 per cent

Shell of Earth's Crust 92.89 per cent

The atmosphere contains about 20 per cent of oxygen, 79 per cent of nitrogen, and 1 per cent of argon. The distribution of the elements in the ocean appears in the following Table of the Approximate Composition of the Ocean

Pee Cent

Oxygen Hydrogen .

Chlorine .

Sodium Magnesium

85.79

10.67

2.07

1.14

.14

Sulphur . . .

Calcium . . .

Bromine . . .

Carbon . . .

Other Elements

Besides the elements which are combined as saline matter, the ocean contains dissolved gases, such as oxygen, nitrogen, and carbon dioxide.

The proportion of the elements in the ten-mile shell of the earth's crust is shown in the following

Table of the Approximate Composition of the Earth's Crust

Pee Cent

Oxygen . .

47.07

Silicon . .

28.06

Aluminium .

7.90

Iron . f .

4.43

Calcium . .

3.44

Potassium .

2.45

Sodium . .

2.43

2.40

Remainder .

1.82

Graphic Proportion

These elements are chiefly in the combined state.

The chemical elements necessary for human beings are shown in the following

Table of the Average Composition of the Human Body

Oxygen . . .

65.00

Phosphorus .

1.00

Magnesium .

0.05

Carbon . . .

18.00

0.35

Iron . . .

0.004

Hydrogen . .

10.00

Sulphur . .

0.25

Iodine . . .

trace

Nitrogen . .

3.00

Sodium . .

0.15

Fluorine . .

trace

Calcium . .

2.00

Chlorine . .

0.15

Silicon • . .

trace

The following is a

Table of the Less Common Elements and their Symbols

Name

Argon .

Beryllium

Csesium

Cerium .

Columbium

Erbium

Europium

Gadolinium

Gallium

Germanium

Helium .

Indium .

Iridium

Krypton

Lanthanum

Molybdenum

Neodymium

Neon . .

Osmium

Palladium .

Praseodymium

A

Be

Cs

Ce

Cb

Er

Eu

Gd

Ga

Ge

He

In

Ir

Kr

La

Mo

Nd

Ne

Os

Pd

Pr

Name

Radium .

Rhodium .

Rubidium Ruthenium Samarium Scandium Selenium .

Tantalum Tellurium Terbium .

Thallium .

Thorium .

Thulium .

Titanium .

Tungsten .

Uranium .

Vanadium Xenon Ytterbium Yttrium .

Zirconium

Ra

Rh

Rb

Ru

Sm

Sc

Se

Ta

Te

Tb

Tl

Th

Tm

Ti

W

U

V

Xe

Yb

Yt

Zr

The symbols of the chemical elements, as may be seen in the foregoing tables, are in some instances the first letter of the common name of the element. Thus, O is the symbol of oxygen, H of hydrogen, N of nitrogen. But since several elements have the same initial letter, the symbol of some elements contains two letters. Thus, C represents carbon, while the symbol of calcium is Ca, of chlorine CI, of chromium Cr, and of copper Cu. The symbols of several elements, especially the metals so long known, are derived from their Latin names. Thus, we have a

Table of the Chemical Elements with Latin Symbols

Latin Name

Latin Name

Antimony .

Stibium

Sb

Hydrargyrum

Hg

Copper . .

Cuprum

Cu

Potassium .

Kalium

K

Gold . . .

Aurum

Au

Silver . .

Argentum

Ag

Iron . . .

Ferrum

Fe

Sodium . .

Natrium

Na

Lead . . .

Plumbum

Pb

Tin . . .

Stannum

Sn

The symbols of the elements always begin with a capital letter, and are not followed by a period. They should be learned by actual use. Their full significance w t :11 be explained in later chapters.

Chemical Compounds. — A chemical compound is a substance which is composed of two or more chemical elements. There is a very large number of chemical compounds. The elements which make up a chemical compound are called its constituents. Chemical compounds differ fundamentally from elements in having three essential characteristics. (1) Their constituents are not mixed, but are united chemically. That is, the chemical energy originally possessed by the elements that make up compounds has so operated that the new substance (i.e. the compound) cannot be separated into its constituents except by the application of some form of energy, such as heat, light, electricity, etc. Thus, water is a compound of the elements oxygen and hydrogen, which cannot be separated from each other unless water is subjected to intense heat or to electricity. (2) In any given chemical compound the constituents are always the same and are present in a fixed ratio by weight. Thus, sodium chloride contains 39.34 per cent of the element sodium and 60.65 per cent of the element chlorine. (3) The properties of a compound differ from those of its constituent elements. Thus, the blue solid copper sulphate is a compound of three elements, — the red metal copper, the yellow non-metal sulphur, and the colorless gas oxygen.

Chemical compounds must not be confused with mixtures. The components of a mixture may vary in nature and in proportion ; they are also not combined chemically but held together loosely, and can be separated by some mechanical operation, as filtering or sifting, without bringing about any chemical change by the application of energy. A mixture, too, generally has properties which are similar to, or are an average of, those of its components.

1. Solve the problems on the metric system in the Appendix, § 1.

2. Assuming that the ten-mile shell of the earth's crust weighs 900 trillion metric tons, calculate the weight of each abundant element in it. (See page 11.)

3. Calculate the weight of each element in a human body weighing 70 kilograms. (See page 12.)

4. Calculate the number of grams in 52 kilograms of typical ocean water.

CHAPTER II Oxygen — Ozone

Oxygen has played an important part in the development of chemistry, and is an appropriate element with which to begin a systematic study of this science.

Occurrence. — Oxygen is the most abundant and widely distributed of the elements, and occurs both free and combined. Mixed with nitrogen and a few other gases, it forms nearly 21 per cent (by volume) of the atmosphere. Combined with hydrogen, it constitutes eight ninths (by weight) of water; combined with silicon and certain metals, it makes up nearly half of the earth's crust; while compounds of oxygen with carbon and hydrogen form a large part of animal and vegetable matter. Thus, the human body contains about 65 per cent of oxygen (see page 12), and starch, which is a component of all plants, contains 50 per cent.

Preparation. — Oxygen can be obtained from its compounds or from air. It was first prepared by decomposing a compound of oxygen and mercury called mercuric oxide. When heated, this compound decomposes into oxygen and mercury; the oxygen escapes as a gas, and the mercury condenses as globules or a film on the upper part of the glass vessel in which the experiment may be conveniently performed. This experiment is historically interesting, because it was first performed by Priestley, the discoverer of oxygen. (See Discovery of Oxygen, below\)

The gas is often prepared by decomposing potassium chlorate — a compound of oxygen, chlorine, and potassium. If heated to a rather high temperature, the potassium chlorate ' passes through a series of changes which result finally in the liberation of all the oxygen and the formation of a compound of potassium and chlorine called potassium chloride.

Oxygen is most conveniently prepared in the laboratory by heating a mixture of potassium chlorate and manganese

Fig. 1. — Apparatus for preparing and collecting oxygen in the laboratory. The oxygen mixture is put in A and heated. The oxygen gas escapes through B-C-D into the pneumatic trough (E). The latter is filled with water until the shelf is covered and a bottle full of water is then placed mouth downward on the shelf. The oxygen bubbles through the hole in the shelf up into the bottle and displaces the water.

dioxide in a glass or metal vessel, and collecting the liberated oxygen in a bottle by means of a pneumatic trough. (See Fig. 1.) The gas is liberated freely from this mixture at a lower temperature than when either compound is heated alone. Large quantities of oxygen are prepared for commercial purposes by heating a mixture of potassium chlorate and manganese dioxide in an iron vessel.

Other commercial processes are used. In Brin's process, which is operated largely in England, purified air is forced by a pump over barium oxide heated to about 700 degrees C., 1 thereby forming barium dioxide. The air supply is then cut off, and the pressure in the retorts reduced by reversing the pump. This operation changes the barium dioxide back again into barium oxide and oxygen. The gas is drawn off into a reservoir. The process is then repeated.

Oxygen can be prepared from water. When an electric current is passed through water containing sulphuric acid or sodium hydroxide, oxygen (and also hydrogen) is liberated.

Oxygen can also be separated from liquid air. (See Liquid Air.) By allowing liquid air to evaporate at ordinary temperature and pressure, the nitrogen escapes from the liquid air more rapidly than the oxygen, leaving finally a liquid which is nearly pure oxygen. Unlimited quantities of oxygen may probably thus be cheaply prepared from the air.

Oxygen can be prepared from sodium peroxide (or from oxone — a special form of this compound) by allowing it to interact with water. This is a convenient method for preparing a small quantity of the gas.

Chemical Changes illustrated by the Preparation of Oxygen. — Brief reference has already been made to the four main kinds of chemical change, viz. decomposition, combination, substitution, and double decomposition. The first and second kinds are illustrated by some of the methods for the preparation of oxygen. When mercuric oxide is heated,

1 C. is the abbreviation of "centigrade," which is the name of the thermometer used in science. This thermometer registers 100 degrees at the boiling point of water, and degrees at the freezing point. (See Appendix, §2.)

it decomposes into oxygen and mercury. Energy in the form of heat serves to start and maintain the chemical change, and if heat were supplied long enough, all the compound would be decomposed into the two elements oxygen and mercury. A chemical change whereby a compound with a definite set of properties decomposes into two elements each with its own set of properties is the simplest illustration of the kind of chemical, change called decomposition. This fact might be compactly expressed by an equation, thus: —

Mercuric Oxide = Mercury + Oxygen.