Complete Text (Part 18)

hydrogen atom. No one atom of any other element can combine with more AIE AND WATER — NITROGEN, OXYGEN AND HYDROGEN 181 than four oxygen atoms unless the compound contains more than two elements. At ordinary temperatures oxygen exhibits no great inclina- tion to enter rapidly into combination with other elements except with phosphorus and with the elements called the alkali metals; but many elements are oxidized at higher temperatures and many are slowly oxidized by oxygen at the common temperature. 281. Ozone is a gas consisting of oxygen alone but differ- ing decidedly from ordinary oxygen, ozone being much more active in causing oxidation. The difference between ordinary oxygen and ozone is due to the fact that each individual particle of common oxygen (02) consists of only two atoms, while each individual particle of ozone consists of three atoms (03). 282. Oxidation signifies, in the narrowest sense of the term, the chemical combination of any element with oxygen. Fire is a violent or rapid chemical process by which the burning substances, or one or more of their component ele- ments, enter into chemical combination with the oxygen of the air. This rapid oxidation is called combustion and pro- duces heat, the intensity of which is in direct proportion to the velocity of the oxidation and dependent also upon the kind and quantity of the fuel "consumed." The elements of greatest importance as fuel are carbon and hydrogen in combination with each other and with other elements, or carbon alone. When carbon undergoes combustion it combines with oxygen to form oxides of carbon. Eespiration is attended with "slow combustion," by which certain substances contained in the venous blood entering the lungs are " oxidized" by the oxygen of the air inspired into those organs, and this process is a heat-producing chemical action. Slow oxidation may be seen not only in the results of 182 A CORRESPONDENCE COURSE IN" PHARMACY respiration but also in many other phenomena, as, for instance, in the tarnishing of iron and some other metals when exposed to moist air. 283. Oxides. Any compound consisting of only two ele- ments, one of which is oxygen, is called an oxide. But a compound of a metal with oxygen is a salt if a part of the metal performs the basic function and another part the acidic function. Silver oxide is a compound of silver and oxygen ; the metal magnesium forms magnesium oxide; zinc forms zinc oxide. But some elements have more than one oxide. Carbon has two, phosphorus has three, chlorine four, nitrogen five, and manganese seven different oxides; for the elements named, and also many other elements, can combine with oxygen in more than one proportion. Whenever any oxide consists of but two elements, each individual particle or molecule of that oxide, if it contains more than four atoms of oxygen, must contain more than two atoms of the other element ; and two atoms of one kind may hold in combination or be directly united to one, two, three, four, five or seven atoms of oxygen. [Distinction may profitably be made between oxides composed of two elements in which all of the oxygen is directly combined with all of the other element, and the so-called oxides composed of two elements in which two oxygen atoms may" be directly combined with each other. In HOH the oxygen is all combined with all of the hydrogen; but in HOOH each oxygen atom is directly combined with only one of the two hydrogen atoms.] The oxides of the metals are all solids ; but those of the non-metallic elements are some of them solids, others liquids, and others gases. Many of the oxides can be produced by combustion, or by direct combination of oxygen with other elements. AIR AND WATER— NITROGEN, OXYGEN AND HYDROGEN 183 284. Examples of Oxidation by Combustion, (a) Sulphur (S) burns with a blue flame, combining with the oxygen of the air to form that oxide of sulphur which constitutes the familiar, irritating, colorless gas produced when a sulphur match burns. No ash is formed. Each atom of the sulphur combines with two atoms of oxygen; hence the irritant sulphurous oxide is called a dioxide and it is represented by the symbolic formula S02, in which S stands for one atom of sulphur and 02 for two atoms of oxygen. As one atom of sulphur weighs twice as much as one atom of oxygen, it follows that the sulphur dioxide obtained weighs twice as much as the quantity of sulphur "con- sumed." [Another oxide of sulphur exists which cannot be pro- duced by combustion. It is a white solid and it is a trioxide, the composition of which is clearly indicated by its symbolic molecular formula, S03.] (b) When charcoal, which is nearly pure carbon (C), is ignited and "consumed" by fire, or undergoes combustion, the carbon is oxidized. But if the supply of air or oxygen is insufficient the carbon does not combine with the maxi- mum amount of oxygen it can hold in chemical combination, but with only one-half as much. A carbon utom weighs 12 times as much as an atom of hydrogen; but an oxygen atom weighs 16 times as much as a hydrogen atom. The carbon oxide formed by incomplete combustion of the carbon is composed of 12 parts of carbon and 16 parts of oxygen and it is in fact carbon monoxide, or CO. The oxide formed when the carbon undergoes complete combustion is composed of 12 parts of carbon and 32 parts of oxygen, and is in fact carbon dioxide, or C02. Both of the oxides of carbon are colorless gases. They are the only two oxides carbon can form. 184 A CORRESPONDENCE COURSE IN PHARMACY Carbon monoxide is combustible. It burns in the air with a blue flame, taking up from the air as much more oxygen as it already contains, being thus oxidized to carbon dioxide. This oxidation is represented symbolically as follows: CO+0=C02. But carbon dioxide is not combustible, because carbon can- not hold in combination with itself more than 2f times its own weight of oxygen, or, in other words, because one carbon atom cannot hold more than two oxygen atoms in direct combination if the compound contains no other element. When pure carbon is thus oxidized no ash is formed. Twelve kilograms of carbon consume for complete oxidation thirty-two kilograms of oxygen, producing forty-four kilo- grams of carbon dioxide. (c) Alcohol is composed of the three elements carbon, hydrogen and oxygen. When it is ignited and burns in a free supply of air the flame is smokeless, the combustion is complete, no ash or residue is left, and the products are carbon dioxide, C02, and water, H20. Each molecule of alcohol is composed of two atoms of carbon, six atoms of hydrogen and one atom of oxygen. Its molecular formula is, therefore, empirically written C2H60. Hence, each mol- ecule of alcohol weighs 46 times as much as one hydrogen atom. Each molecule of alcohol requires 6 additional atoms of oxygen for the formation of two molecules of carbon dioxide and three molecules of water. Accordingly, the combustion of alcohol is represented by the chemical equation, C2H60+60=2C02+3H20. Hence, 46 kilograms of alcohol will require 96 kilograms of oxygen for complete combustion and the products will be 88 kilograms of carbon dioxide and 54 kilograms of water vapor. AIR AND WATER — NITROGEN, OXYGEN AND HYDROGEN 185 (d) Wood is a complex mixture of organic substances com- posed mainly of carbon, hydrogen* and oxygen, but contain- ing also some compounds of potassium, calcium and other elements. When wood is used as fuel the products of the combustion are chiefly the oxides of carbon and hydrogen, which we have already mentioned. These pass off, together with some "unconsumed" carbon and other matter, as smoke, while the compounds of potassium, calcium, aluminum, silicon and other "mineral matters" contained in the wood form the ash. (e) When the soft white metal called magnesium (Mg) is ignited it burns rapidly, emitting an intense white light as it unites with the oxygen of the air to form a white solid, which is magnesium oxide, MgO. The "flash light" powder used by photographers consists of or contains powdered mag- nesium. No gas is formed in the combustion of magnesium, for the only product is the oxide, which is a fine powder, forming a cloud of white dust but no smoke. Thus the only product here is the ash. Five grams of this white ash is produced out of every three grams of the metal, because a mass of 3 grams of magnesium unites with 2 grams of oxygen. Magnesium and oxygen unite with each other in no other proportions. Hence, we see that when magnesium is "con- sumed" by combustion it yields in fact a product weighing 66 per cent more than the metal consumed. Magnesium oxide is commonly called "magnesia." (/) When the black mineral called antimonite, or "black sulphide of antimony," which is composed of the elements antimony (Sb) and sulphur (S), is strongly heated or "roasted" in the air it decomposes. As one molecule of the black sulphide of antimony is composed of 2 atoms of anti- mony and three atoms of sulphur its symbolic formula is written Sb2S3. The antimony is oxidized by the oxygen of 186 A CORRESPONDENCE COURSE IN PHARMACY the air to antimony oxide, Sb203, which fuses and forms a glass-like solid, while the sulphur forms the gas S02. As the atomic weight of antimony is 120, because any given number of atoms of antimony weigh 120 times as much as the same number of atoms of hydrogen, it follows that when 336 grams of Sb2S3 is completely oxidized to Sb203 and S02, the quantity of oxygen required must be 144 grams, and that the combustion or oxidation is represented by the equation, Sb2S3+90=Sb203+3S02. From these examples the student will learn that fire or combustion does not change the amount of matter in the universe ; it simply alters the composition and form of matter by rearrangements of the atoms into other kinds of mol- ecules ; and that the weight of the product or products formed by a burning substance is greater than that of the substance burned by just the amount of oxygen taken up in combination to form the new substance or substances. 285. Water is one of the most plentiful oxygen compounds in nature. It is a most wonderful substance, composed of two of nature's most remarkable elements, hydrogen (H) and oxygen (0). In each molecule, or smallest possible individual particle of water, there are two hydrogen atoms and one atom of oxygen. Its molecular formula is, therefore, written H20 ; but it may also, and preferably, be represented by the formula HOH. Water forms solutions of numerous kinds of matter and is indispenable to circulation and nutrition in plants and animals, rendering possible the chemical processes without which life in the world of matter must cease. It is the most, neutral or chemically indifferent substance with regard to the vast majority of other kinds of matter, serving there- fore a3 a medium in which other substances may be liquefied, whereby their molecules acquire greater freedom of motion, AIR AND WATER — NITROGEN, OXYGEN AND HYDROGEN 187 so that they can readily act upon each other. Its power to cause the dissociation of certain kinds of molecules into their component "ions" is referred to elsewhere. Molecules of water have a remarkable power and tendency to enter into some form of combination with other kinds of molecules, as "water of crystallization" and in other ways. Its uses in the economy of nature, in sanitation, and in the indus- tries of civilization could not be subserved by any other sub- stance known. Water freezes at 0° C. (32° F.). Its boiling point is 100° C. (212° F.). It attains its maximum density at 4° C. (39.2° F.). One liter of water at 4° C. in vacuo weighs 1 kilogram. One milliliter weighs 1 gram. Six pints of water (96 fluid ounces) weighs approximately 100 avoirdupois ounces. 286. Hydrogen is a colorless, odorless, tasteless, highly inflammable gas. It is the lightest of all kinds of matter, occupying nearly 14^- times as much space as is taken up by an equal weight of air, and about 11,160 times as much space as is occupied by an equal weight of water at 0° C. One cubic-decimeter of pure hydrogen at 0° 0., bar. 760 mm., weighs about 0.09 gram. Hydrogen has been obtained in liquid form at a temper- ature estimated to be below —200° 0., and under a pressure of 40 atmospheres. This element exists in nature in the free state only in extremely small quantities. In chemical combination it constitutes about 1 per cent by weight of the whole mass of the earth. Its most abundant compound is water. Hydro- gen is a constituent of nearly all of the carbon compounds of the animal and vegetable kingdoms, and of coal oil, "natural gas" and other bituminous products. 287. Hydrogen is easily prepared by the action of zinc on 188 A CORRESPONDENCE COURSE IN" PHARMACY diluted sulphuric acid. Ordinary sulphuric acid is a hydrogen sulphate composed of two hydrogen atoms, one atom of sul- phur, and four oxygen atoms. Its molecular formula, repre- senting its composition, is best written (HO)2S02. When zinc (Zn) is added to a solution of sulphuric acid (or " diluted sulphuric acid") the zinc takes the place of the hydrogen, forming zinc sulphate, and the hydrogen is set free : Zn+(HO)2S02=Zn02S02+2H. Hydrogen can also be made by passing steam (water vapor) over coal heated to a very high temperature. Carbon mon- oxide (CO) is formed at the same time, the reaction being HOH+C=CO+2H. By the action of sodium hydroxide upon sodium formiate a perfectly pure hydrogen may be made : NaOH+NaCH02=Na2C03+2H. 288. Chemically considered, hydrogen is extremely im- portant. Its properties place it between the metals and the non-metallic elements. It forms no true chemical com- pound with any true metal, but combines with all non- metallic elements. Its oxide or hydroxide, water, is neither a base nor an acid ; but if one of the hydrogen atoms of the molecule of water, HOH, be replaced by a non-metallic ele- ment an acid is the result, whereas if a metal (of low combining value or valence) is substituted for one of the hydrogen atoms a base is formed. Hydrogen is contained in all acids. Hydrogen does not at ordinary temperatures display any inclination to enter into chemical combination with other elements, but a mixture of hydrogen and chlorine, or of hydrogen and oxygen, may be exploded by an electric spark or by ignition. The most intense heat that can be produced by combustion is that produced by igniting a mixture of hydrogen and oxygen in the proportions required to form water. Practical AIR AND WATER — NITROGEN, OXYGEN AND HYDROGEN 189 use is made of this in the "oxy-hydrogen blowpipe." By means of this, hydrogen burning in oxygen is thrown against a fragment of lime which quickly rises to an intense white heat and gives off the well-known powerful "lime light." No one atom of any kind can unite directly with (or hold in combination) more than four hydrogen atoms. Carbon and silicon can unite with four hydrogen atoms ; boron, nitrogen, phosphorus, arsenic and antimony each with three ; oxygen, sulphur, selenium and tellurium with two ; and fluorine, chlorine, bromine and iodine each with only one hydrogen atom. ISTo other elements unite directly with hydrogen under any circumstances. Hydrogen forms alloys with a few of the metals, notably palladium. Ammonia (H3N) is the compound formed when one nitro- gen atom is combined with all the hydrogen it can hold in combination. 289. As hydrogen of all elements has the lowest atomic weight, and of all substances the lowest specific weight, and as it has a uniform atomic combining value or valence as low as that of any other element, it has been adopted as the standard of comparison and unit of expression of all such values. Thus the atomic weight of hydrogen is 1, its vapor density is 1, and its valence is 1. 290. Hydrogen and oxygen are chemical opposites. Hydrogen is one of the positive elements ; oxygen is always a negative element. Any element is oxidized whenever it combines with oxygen; it is reduced whenever it combines with hydrogen. An element is reduced whenever its oxygen compound exchanges its oxygen for hydrogen. An element is oxidized whenever its hydrogen compound exchanges its hydrogen for oxygen. Any element is positive whenever it is in direct combination with oxygen ; it is negative when- ever it is in direct combination with hydrogen. 190 A CORRESPONDENCE COURSE IK PHARMACY Test Questions 1. What is the weight of one liter of pure dry air at 25° C. under the pressure of one atmosphere? 2. Is air a chemical compound ? 3. Is water a chemical compound ? 4. Why are nitrogen compounds generally unstable ? 5. What is the proper technical name of so-called "laugh- ing gas"? 6. Name one common nitrogen compound having a decided odor. 7. What is the algebraic combining number of nitrogen in 9 H4NC1 and in N205 8. Mention ten compounds containing oxygen. 9. Can oxygen be obtained from air ? 10. How is oxygen generally produced ? 11. What is the difference between oxygen and ozone ? 12. Name several examples of simple oxidation. 13. What is the composition of calcium oxide? 14. What is the composition of potassium oxide ? 15. What is the composition of aluminum oxide ? 16. What is the percentage of oxygen in S03 ? 17. What are the products of the combustion of charcoal ? 18. What are the products of the combustion of hydro- carbons ? 19. What is the composition of the ash left