An introduction to the study of inorganic chemistry

Introduction

PAGE

Natural Sciences — Physical and Chemical Changes — Chemical and Physical Properties — Energy — Matter — Mechanical Mixtures — Chemical Compounds — Elements 7

CHAPTER n.

OXYGEN.

History — Occurrence — Preparation — Properties — Oxidation — Combustion — Kindling Temperature — Oxides — Ozone — Measurements of Gas Volumes 18

CHAPTER HI.

HYDROGEN.

Historical — Occurrence — Preparation — Properties — Reduction — Oxyhydrogen Blowpipe — Blast Lamp — Uses of Hydrogen SS

CHAPTER IV.

COMPOUNDS OF HYDROGEN AND OXYGEN — WATER AND HYDROGEN-

DIOXIDE.

Historical — Composition of Water — Occurrence — Impurities in Water — Purification of Water — Properties — Water of Crystallization — Uses of Water — Preparation, Properties and Uses of Hydrogen Dioxide. 46

CHAPTER V.

ATOMIC THEORY.

Fundamental Laws of Matter — Atomic Theory — Value of a

Theory — Atomic Weights 63

CHAPTER VI.

CHEMICAL EQUATIONS AND CALCULATIONS.

Formulas — Equations — Kinds of Reactions — Chemical Equations are Quantitative — Heat of Reaction 71

4 Contents.

CHAPTER VII.

JiflTROGEN AND THE RARE ELEMENTS — ARGON — NEON — HELIUM — KRYPTON — XENON.

PAGE

Historical — Occurrence of Nitrogen — Preparation — Properties — Rare Atmospheric Elements 79

CHAPTER VIII.

THE ATMOSPHERE.

Constituents Essential to Life — The Function of Each — Constituents not Essential to Life — Quantitative Analysis of Air — Air a Mechanical Mixture — Changes in the Atmosphere due to Respiration and Combustion — Properties of Ihe Atmosphere — Liquid Air 83

CHAPTER IX.

SOLUTIONS.

Solution of Gases in Liquids — Solution of Solids in Liquids — Saturated Solutions — Crystallization — Properties of Solutions — Electrolytic Dissociation 91

CHAPTER X.

ACIDS, BASES, SALTS, VALENCE.

Acids — Properties Common to Acids — Bases — Properties Common to Bases — Salts — Properties Common to Salts — Neutralization and the Dissociation Theory — Metals — Replacing Power of the Metals — Valence — Structure of Compounds — Nomenclature of Acids, Bases and Salts — Acid, Basic and Normal Salts 100

CHAPTER XI.

COMPOUNDS OF NITROGEN.

Decomposition of Organic Matter — Ammonia — Preparation of Ammonia — Properties of Ammonia — Volume Relation of Combining Gases — Nitric Acid — Preparation of Nitric Acid — Law of Mass Action — Properties of Nitric Acid — Nitrates — Nitrous Oxide — Preparation and Properties — Nitric Oxide — Preparation and Properties — Nitrogen Peroxide — Preparation and Properties — Anhydrides 112

Contents. 5

CHAPTER XII.

SULPHUR.

PAGE

Occurrence — Extraction — Physical Properties — Crystallography — Allotropic Forms of Sulphur — Chemical Properties — Hydrosulphuric Acid — Preparation and Properties

— Sulphur Dioxide — Preparation and Properties — Sulphur Trioxide — Preparation — Catalysis — Properties of Sulphur Trioxide — Sulphuric Acid — Manufacture — Properties — Sulphates — Thiosulphates — Monobasic and Dibasic Acids

— Carbon Disulphide — Comparison of Sulphur and Oxygen — Selenium and Tellurium 126

CHAPTER XIII.

THE PERIODIC LAW.

Natural Grouping of Elements — Metals and Non-Metals — Triad Families — Periodic Law — Periodic Table — Value of Periodic Law — Imperfections of the Law 144

CHAPTER XIV.

THE CHLORINE FAMILY.

Fluorine — Occurrence — Preparation — Properties — Hydrofluoric Acid — Preparation and Properties — Fluorides — Chlorine — Historical — Occurrence — Preparation — Properties — Bleaching — Nascent State — Hydrochloric Acid — Preparation and Properties — Aqua Regia — Oxygen Compounds ^ of Chlorine — Bromine — Occurrence — Preparation and Properties — Hydrobromic Acid — Preparation and Properties — Oxygen Compounds — Iodine — Occurrence — Preparation and Properties — Hydriodic Acid — Preparation and Properties 152

CHAPTER XV.

CARBON AND SOME OF ITS SIMPLER COMPOUNDS.

Occurrence — Forms of Carbon — Properties of Carbon — Uses

— Fuels — Hydrocarbons — Marsh Gas r— Acetylene — Other Hydrocarbons — Carbon Dioxide — Preparation — Properties — Carbonic Acid and the Carbonates — Carbon Dioxide and the Plant Life — Carbon Monoxide — Preparation and Properties — Hydrocyanic Acid 169

6 Contents.

CHAPTER XVI.

FLAMES — ILLUMINANTS.

PAGE

Flames — Supporter of Combustion — Appearance of Flames — Structure of Flames — Oxidizing and Reducing Flames — Luminosity of Flames — Bunsen Flame — Blowpipe Flame '

— Coal Gas — Water Gas — Natural Gas — Electric Furnace 183

CHAPTER XVn.

MOLECULAR WEIGHTS — ATOMIC WEIGHTS — FORMULAS.

Determination of Equivalents — Relation of Equivalents to Atomic Weights — Combining Weights — Determination of Molecular Weights — Avogardro's Hypothesis — Hydrogen as Standard — Deduction of Atomic Weights — Raoult's Laws — Law of Dulong and Petit — Determination of Formulas 192

CHAPTER XVHL

THE NITROGEN FAMILY.

Phosphorus — Occurrence — Preparation — Properties — Phosphine — Oxides of Phosphorus — Acids of Phosphorus — Fertilizers — Arsenic — Occurrence — Preparation — Properties — Arsine — Marsh's Test — Oxides of Arsenic — Acids of Arsenic — Sulphides of Arsenic — Antimony — Occurrence — Preparation — Properties — Stibine — Acids of Antimony — Sulphides of Antimony — Metallic Properties of Antimony — Bismuth — Occurrence — Preparation

— Properties — Compounds 203

CHAPTER XIX.

SILICON — BORON.

Preparation of Silicon — Properties — Silicon Hydride — Silicides — Silicon Dioxide — Properties — Silicic Acids — Glass — Boron — Occurrence — Preparation and Properties — Oxides — Acids — Borax 219

CHAPTER I.

INTRODUCTION.

The Natural Sciences. Before we advance very far in the study of nature, it becomes evident that the one large study must be divided into a number of more limited ones for the convenience of the investigator as well as of the student. These more limited studies are called the Natural Sciences.

Since these divisions are made for mere convenience, and not because there is any division in nature itself, it often happens that the different sciences are very intimately related, and a thorough knowledge of any one of them involves a considerable acquaintance with several others. Thus the botanist must know something about animals as well as about plants ; the student of human physiology must know something about physics, as well as about zoology^ and anatomy.

Mineralogy, Physics and Chemistry. Mineralogy, physics and chemistry form a group of sciences related in this close way, and it is not an easy matter to make an exact definition of any one of them. In a general way, However, it may be said that mineralogy deals with the composition and properties of the various substances which compose the earth's crust and with their distribution in nature. Chemistry and physics have for their object the study of the laws which govern the composition of all substances, the properties of substances and the changes which they can be made to undergo.

- (7)

Two Kinds of Changes in Matter. An examination of these changes shows that they can all be classified under two heads : those in which no new kind of matter is formed, and those which result in the formation of new substances with new properties. The former are called physical changes, the latter chemical changes.

1. Physical Changes. When a stick is broken, the pieces do not differ from the original stick save in size; the position of substances often changes, as when the leaves fall or trees are blown down ; a piece of iron may be magnetized ; substances may be changed from cold to hot as the iron heated by the blacksmith in his forge, or the filament of the incandescent, lamp heated by the electrical current. In none of these changes is a new substance formed having a composition different from the substance undergoing the

■ change. Such changes are called physical changes.

2. Chemical Changes. In many other cases the substances undergoing change lose their characteristic properties and are converted into new substances. When a piece of coal or a stick of wood burns, it disappears as such, and in its place we have ashes and invisible gases. Gun-

* powder, when ignited, explodes, and nothing but smoke and gases are found in its place. Sweet fruit juices ferment, and are changed into sour vinegar. Such changes are evidently quite different from the physical changes just mentioned. New substances are formed in place of the ones undergoing change. These changes are called chemical changes.

Changes in Physical State. It is not always easy to tell to which class a given change belongs, and many will require careful thought on the part of the student. One class of changes should be noted with especial care, since it is likely to prove misleading. It is a familiar fact that when water is cooled sufficiently it changes to ice ; when heated to the boiling point it changes to steam. Here we

Introduction, 9

have three different substances, water, ice and steam, one a liquid, one a soHd and one a gas, the properties of which differ widely. Apparently these are chemical changes. A careful study, however, shows that the composition of the three is just the same: they are all composed of the same substances, and in the same proportion. Many other solids can be melted into liquids without undergoing change in composition. Familiar instances are the melting of butter, wax and metals. The change of liquids into vapors is quite as common, but not so often noticed. In general almost any substance can exist in the three conditions, solid, liquid and gas, and we speak of them as the three physical states of matter.

Chemical and Physical Properties. Many properties of a substance can be noted without causing the substance to undergo chemical change. Among these are its color, odor, taste, size, shape, weight, physical state. These are called its physical properties. Other properties are only discovered when the substance undergoes chemical change. These are called its chemical properties. Thus we find that coal burns in air, gunpowder explodes when fired, milk sours when exposed to air.

Tv70 Factors in all Changes. In all the changes which matter can undergo, whether physical or chemical, two factors must be taken into account viz. energy and matter.

I. Energy. It is a familiar fact that certain bodies have the power to do work. Thus water falling from a height upon a water wheel turns the wheel and in this way does the work of the mills. Magnetized iron attracts iron to itself and the motion of the iron as it moves towards the magnet can be turned into work. Coal on burning causes the engine to move and transports the loaded cars from place to place. When a body has this power to do work it is said to possess energy.

lo Inorganic Chemistry.

Law of Conservation of Energy. Careful experiments have shown that when one body parts with its energy, the energy is not destroyed but is transferred to another body or system of bodies. Just as energy can not be destroyed, neither can it be created. If a body gains a certain amount of energy, some other body has lost an equivalent amount. These facts are summed up in the law of conservation of energy which states that energy can neither he created nor destroyed, the amount of it in the universe being constant.

Transformations of Energy. Although energy can neither be created nor destroyed, it is evident that it may assume many different forms. Thus the falling water may turn the electric generator and generate a current of electricity. The energy lost by the falling water is thus transformed into the energy of the electric current. This in turn may be changed into the energy of motion, as when the current is utilized for propelling the cars, or into the energy of heat and light, as when it is used for heating and lighting the cars. Again the energy of coal may be converted into energy of motion as when it is used as a fuel in steam engines.

bince the energy possessed by coal only becomes available when the coal is made to undergo a chemical change, it is sometimes called chemical energy. It is this form of energy with which we are especially interested in the study of chemistry.

2. Matter. At first sight there appears to be no limit to the kinds of matter of which the world is made. But it has been found that all these varieties may be divided into three classes, viz., mechanical mixtures, chemical compounds and elements. These will now be briefly discussed.

a. Mechanical Mixtures. If equal bulks of common salt and iron filings are thoroughly mixed together, a product is obtained, which, judging by its appearance, is a new substance. If it is examined more closelv however, it will

Introduction.

II

Fig. 1 be seen to be meiely a mixture of the salt and iron, each of v/hich substances retains its own peculiar properties. The mixture tastes just like salt; the iron particles can be seen, :^ and their gritty character detected. A magnet rubbed in the mixture draws out the iron just as if the salt were not there. The salt also can be separated from the iron quite easily. If several grams of the substance is placed in a test tube, and the tube half filled with water and thoroughly shaken, the salt disappears, or dissolves in the water. The iron particles can then be filtered from the liquid by pouring the entire mass upon a piece of filter paper folded so as to fit into the interior of a funnel (Fig. i). The paper retains the solid but allows the clear liquid to drain through. The iron particles so obtained will be found to be identical with the original iron. The iron has undergone no change. The water of the salt solution can be removed by evaporation. To accomplish this, the solution is poured into a small evaporating dish and gently heated (Fig. 2) until the water has all disappeared, or evaporated. The salt is left in the dish and on comparing it with the original salt, it is found to be identical with it. No new substance has been formed by mixing the salt and iron, and the mixture is called a mechanical mixture.

Such mixtures are very common in nature. Thus in a piece of coarse grained granite, three quite different

Fig. 2 substances can be seen and picked out. Gold and sand is a mechanical mixture, for the miner separates them by merely shaking the mixture in a pan, allowing running water to wash away the lighter sand, while the heavier gold sinks to the bottom of the pan. Evidently the composition of such a mixture may vary greatly, and no two mixtures are likely to have the same composition. The ingredients of a mechanical mixture can often, though not always, be separated by mechanical means, such as sifting, sorting, magnetic attraction, or by dissolving one constituent and leaving the other undissolved.

b. Chemical Compounds. If iron filings and powdered sulphur are thoroughly ground together in a mortar, 'a yellowish green substance results. It might easily be taken to be a new compound ; but as in the case of the iron and salt, the ingredients can be readily separated. A magnet draws out the iron. Water does not dissolve the sulphur, but other liquids do, as for instance the liquid called carbon disulphide. When treated with carbon disulphide, the iron is left' unchanged, and the sulphur can be obtained again, after filtering off the iron, by evaporating the liquid. The ^■0 substance is therefore a mechanical

^^ mixture. If now a new portion of

^^s- 3 ^}^g mixture is placed in a dry test

tube and carefully heated in the flame of the Bunsen burner, as shown in Fig. 3, a striking change takes place. The mixture begins to glow at some point, the glow rapidly extending through the whole mass. If the test tube is broken and the product examined, it will be found to be a hard, black, brittle substance, in no way recalling the iron or the sulphur. The magnet no longer attracts it ; carbon disulphid'e will not dissolve sulphur from it. It is a new sub-

Introduction. 13

stance with new properties, resulting from the chemical union of iron and sulphur.

Again if a.^ small quantity of red oxide of mercury is heated in a hard glass test tube, it will be noticed that a bright silvery mirror gradually forms on the walls of the tube a little above the oxide. A glowing spark on a splint of wood, held at the mouth of the tube, bursts into flame, showing that a new, gaseous substance is being produced in the tube. On cooling the tube, the substance forming the silvery mirror does not change back again into the red oxide of mercury. It is a permanent new substance. By heating the red oxide, then, two new substances have been produced : the metalHc substance forming the silvery mirror, and the gas which caused the spark to burst into flame.

\\'hen a substance contains two or more kinds of matter, which are united chemically and cannot be separated by mechanical means, we say that it is a chemical compound. Thus the iron and the sulphur formed a chemical compound when they were heated together ; the red oxide of mercury is a chemical compound, because by chemical decomposition two very different substances can be obtained from it. We shall see later that a chemical compound differs markedly from a mechanical mixture, in that its composition is always exactly the same.

Chemical Affinity the Cause of Chemical Combination. The agency which causes substances to combine, and which holds them together when combined, is called chemical affinity. Yet the experiments just described show that heat is often necessary to bring about chemical action, and that it can also decompose some chemical compounds. The distinction between the cause producing chemical action, and the circumstances favoring it must be clearly made. Chemical affinity is always the cause of chemical union. Many agencies may make it possible for chemical affinity to act by overcoming circumstances which stand in its way. Among these agencies are heat, electricity, and sometimes Hght. As a rule, solution also promotes action between two substances. Sometimes these agencies may overcome chemical attraction, and so occasion decomposition of a compound, as in the case of the decomposition of the red oxide of mercury by heat.

c. Elements. It has been seen that strong heating of red oxide of mercury leads to the formation of two new substances. The question arises do these substances likewise contain other substances ; that is are they also chemical compounds? All efforts have failed to get anything else from them but the metallic substance and the gas. Such substances are called elements. An element then is a substance from which no other substance can be obtained by any known means. It is not always easy to be certain that a given substance is really an element. Some way, as yet untried, may be successful in decomposing it into other simpler forms of matter, and the supposed element will then prove to be a compound. Water, lime and -many other familiar compounds were at one time thought to be elements.

Alchemy. In olden times it was thought that some way could be found to change one element into another, and a great many efforts were made to accomplish this transformation. Most of these efforts were directed toward changing the commoner metals into gold, and many fanciful ways for doing this were described. The chemists of that time were called Alchemists, and the art which they practiced was called Alchemy. The Alchemists gradually became convinced that the only way common metals could be changed into gold was by the wonderful power of a magic substance which they called the Philosopher's Stone, which would accomplish this transformation by its mere touch, and would in addition give perpetual youth to its fortunate possessor. No one has ever

Introduction.

found such a stone, and no one has succeeded in changing one metal into another.

Number of Elements. The number of substances now considered to be elements is not large — about eighty in all. Many of these are rare and very few of them make any large fraction of the materials in the earth's crust. Clark gives the following estimate of the composition of the earth's crust:

Silicon 27.-9%

Aluminium 8.1%

Iron 4-7% iMagnesium 2.5%

Sodium 2-7%

Potassium 2 . 4%

Other elements.. 1.2%

It is not necessary to study more than a third of the total number of elements to gain a very good knowledge of chemistry.

Physical State of the Elements. About ten of the elements are gases at ordinary temperatures. Two — mercury and bromine — are liquids. The others are all solids, though their melting points vary through wide limits, from caesium which melts at 16° to elements which do not melt save in the intense heat of the electric furnace.

Occurrence of the Elements. Comparatively few of the elements occur as uncombined substances in nature, most of them being found in the form of chemical compounds. When an elernent does occur by itself, such as gold, we say that it occurs in the free state or native ; when it is combined with other substances in the form of compounds, we say that it occurs in the combined state, or in combination. In the latter case there is usually little about the compound to suggest that the element is present in it; for we have seen that elements lose their owm peculiar properties when thev enter into combination with other elements.

It would never be suspected that the red oxide of mercury contains a bright silvery metal, or that the eddish, earthy looking iron ore contains iron.

Names of Elements. The names given to the elements have been selected in a great many different ways. Some are very old and their original meaning is obscure. Such names are iron, gold, copper. Many indicate some striking physical property of the element. The name bromine is derived from a Greek word meaning a stench, referring to the extremely unpleasant odor of the substance. The name iodine comes from a word meaning violet, alluding to the beautiful viokt color of iodine vapor. Some names indicate prominent chemical properties of the elements. Nitrogen means the producer of nitre, nitrogen being a constituent of nitre or saltpetre. Hydrogen means the producer of water, since the element forms water when burned. Others are named from mythology, as tantalum ; or from countries or localities, as germanium, and columbium.

Symbols. In indicating the elements found. in compounds it is inconvenient to use such long names ; hence chemists have adopted a system of abbreviations. Sometimes the initial letter of the name will suffice to indicate the element. Thus I stands for iodine, C for carbon. Usually it is necessary to add some other characteristic letter of the name, since several names may begin with the same letter. Thus C stands for carbon, CI for chlorine, Cd for cadmium, Ce for cerium, Cb for columbium. Sometimes the symbol is an abbreviation of the old Latin name. In this way Fe (ferrum) indicates iron, Cu (cuprum) copper, Au (aurum) gold. These abbreviations are called symbols. They will become familiar through constant use.

Law of Conservation of Matter. It has been seen tjiat matter often changes much in appearance ; elements

Introduction. ly

unite to form compounds which can be decomposed again into elements. In all such transformations it has been found that the amount of matter, or its mass, does not change at all. Xo matter is ever lost or created in these changes. This important truth is called the law of ':on5ervation of matter. The total amount of matter and of energy in the universe thus remains constant, though the form of each mav suffer many changes.

CHAPTER 11.

OXYGEN.

History. The discovery of oxygen is generally attributed to the English chemist Priestley, who in 1774, obtained it by heating a compound of mercury "and oxygen known as mercuric oxide, the oxygen being expelled by theheat. It is probable however that the Swedish chemist Scheele had previously obtained it although an account of his experiments Vv^as not published until 1775. The name oxygen signifies "to make acid." It was given to the element by the French chemist Lavoisier, since he believed that all acids owe their characteristic properties to its presence — a view which we now know to be incorrect.

Occurrence. Oxygen is by far the most abundant of all the elements. It occurs both in the free and in the combined state. 100 volumes of air contain about 21 volumes of free oxygen. In the combined states it forms eightninths of water and nearly one-half of the rocks com|)osing the earth's crust. It is also an important constituent of the compounds which compose plant and animal tissues.

Preparation. Although oxygen occurs in the free state in the atmosphere, its separation from the nitrogen and other gases with which it is mixed is such a difficult matter that in the laboratory it has been found more convenient to prepare it from its compounds. The most important of the laboratory methods are the following:

I. Preparation from Water. Water is a compound containing 11.18% of hydrogen and 88.82% of oxygen. It is easily separated into these constituents by passing a current of electricity through it under suitable conditions. The process will be described in the chapter on water.

Oxygen.

While this method of preparation is a simple one, it is not economical, on account of the cost of the electric current.

2. Preparation from Mercuric Oxide. This method is of interest since it is the one which led to the discovery of oxygen. The oxide is placed in a small glass test tube and heated. The compound is thereby decomposed into mercury which collects on the sides of the glass tube forming a silvery .nirror, and oxygen which, being a gas, escapes from the tube. The presence of the oxygen is shown by lighting the end of a splint, extinguishing the flame and bringing the glowing coal into the mouth of the tube. The oxygen causes the glowing coal to burst into a flame.

In a similar way, oxygen may be obtained from its compounds with some of the other elements. Thus manganese dioxide, a black compound of manganese and oxygen, when heated to a high temperature, loses one-third of its oxygen, while barium dioxide, on heating, loses one-half of its oxygen.

3. Preparation from Potassium Chlorate. This is the method usually employed in the laboratory. Potassium, chlorate is a white solid composed of 31.9% potassium,

28.9% chlorine and 39.1% oxygen. When heated it undergoes a series of changes in which the oxygen is finally all set free, leaving a compound of potassium and chlorine called potassium chloride. The change mav be represented as follows :

potassium

chlorine = oxygen (potassium

chlorate)

potassium chlorine

(potassium chloride)

Fig. 4

The evolution of the oxygen begins at about 400®. It has been found however that if the potassium chlorate is mixed with about one-fourth its weight of manganese dioxide, the oxygen is given off at a much lower temperature. Just how the manganese dioxide brings about this result is not definitel)^ known. The amount of oxygen obtained from a given weight of potassium chlorate is exactly the same whether the manganese dioxide is present or not. So far as can be detected the manganese dioxide undergoes no change. ^^^- ^ The manner of preparing oxygen

by this process is illustrated in the accompanying diagram (Fig. 4). A mixture composed of i part of manganese dioxide and 4 parts of potassium chlorate is placed in the flask A and gently heated. The oxygen is evolved and escapes through the tube B. It is collected by bringing over the end of the tube, the mouth of a bottle completely filled with water and inverted in a vessel of water as shown in the figure. The gas rises in the bottle and displaces the water. In the preparation of large quantities of oxygen, a copper retort, (Fig. 5) is often substituted for the glass flask.

This method of collecting oxygen illustrates the general method used for collecting such gases as are insoluble in water or nearly so. The vessel C, (Fig. 4), containing the water in which the bottles are inverted, is called a "pneumatic trough."

4. Commercial Methods of Preparation. Oxygen can now be purchased stored under great pressure in strong steel cylinders. This is prepared either by heating a mixture of potassium chlorate and manganese dioxide or by separating it from the nitrogen and other gases with which it is mixed in the atmosphere. Different methods have been employed for accomplishing this separation. The most important of these at the present time consists in liquifying the air by subjecting it to intense cold and great pressure. When the pressure is removed, the liquid nitrogen present evaporates first, leaving the liquid oxygen. As this evaporates the gas is pumped under high pressure into a strong steel cylinder

Oxygen.

(Fig. 6) provided with a screw valve, so that the __^ oxygen may be drawn off at will. Oxygen so prepared is never entirely free from nitrogen, often containing as much as 15 to 20% of it.

Physical Properties. Oxygen is a colorless, odorless, tasteless gas, slightly heavier than air. One liter of it weighs 1.428 grams, at a temperature of 0° and under a pressure of one atmosphere (1033 grams per square centimeter), while under similar conditions one liter of air weighs 1.292 grams. It is but slightly soluble in ' water. As in the case of other gases, oxygen may be liquefied by applying very great pressure to the highly cooled gas. When the pressure is removed, the liquid oxygen rapidly boils, passing again into the gaseous state, since its boiling

Fig.