Elementary chemistry for high schools and academies

Front matter

Class QT .

Book Jll4S

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Chapter I Chemical Action

1. Elements and Compounds. — The different kinds of natter known to man may be divided into two classes :

(1) Compounds, or those which may be decomposed or eparated into other substances.

(2) Elements, or those which have thus far resisted all attempts to decompose them.

About seventy simple substances or elements have been liscovered, and, so far as is at present known, all compounds are the result of the chemical union of two or more 3f these.

It is possible that, as our knowledge of chemistry in- 3reases, many, if not all, of the substances now classed as elements may be shown to be compounds. Water was considered an element until 1783, and several other so-called elements have been resolved into simpler forms since that time.

There are many chemists who consider the seventy elements as so many unsolved problems.

2. Molecules and Atoms. — The accepted theory of the constitution of matter maintains : —

1. That it is made up of minute particles called molecules (little masses), each one of which, in a given substance, is exactly like its neighbors in weight, volume, and structure.

2. That they move about each other, under the influence of heat, as separate bodies.

3. That they are the limit beyond which it is impossible to subdivide matter without destroying its identity.

In accordance with this theory, each molecule of a compound is believed to contain the same elements that chemical analysis shows the large masses of the substance to contain, and these smaller portions of the elements are called atoms. There is good reason for believing that atoms rarely exist in a free state, but that the molecules of most elements consist of two or more atoms.

A molecule is the smallest particle of a substance which can exist in the free state, and which has the same composition as din/ larger mass of the same substance.

.1// atom is tin* smallest particle of an element that exists in (in'/ molecule.

We may now state the following definitions : —

.1 compound is a substance whose molecule contains two or more kinds of atoms.

.1// element is a substance ichose molecule contains only one kind of atoms.

3. The Domain of Chemistry. — Chemistry is that branch of science which deals with, changes in the identity of substances; and ivith the laws, causes, and effects of such changes.

The subject is closely related to physics ; every chemical change is accompanied by some physical change, but the chemical change differs in one important particular from a physical change: the chemical change is due to forces acting upon atoms, while the physical change depends upon forces acting upon the molecule.

A physical change is one which does not destroy the identity of the substance acted upon.

CHEMICAL ACTION 3

Illustration. When a bar of steel is magnetized it acquires a new property, but it remains the same substance, and the change is physical.

A chemical change is one which destroys the identity of the substance acted upon.

Illustration. When a bar of steel rusts a portion of the steel is converted into a new substance which differs from the steel in color, tenacity, elasticity, and other properties.

4. Chemical Action. — In some instances one may be in doubt as to whether a chemical change has taken place, and in a few instances chemical analysis is necessary to prove it. But in general the occurrence of any of the following phenomena, when two or more substances are mixed, may be taken as evidence of chemical action : —

1. Effervescence.

2. The evolution of heat and light.

3. Change of color.

4. Change of volume.

5. Change of state.

6. The development of electricity.

Exceptions. 1. A change of state by solution of a solid or gas.

2. A change of volume due to the absorption of a gas by a solid or liquid, or to- a change in temperature.

Take notes on the following experiments which will be performed for you, and designate them as physical or chemical changes : —

Experiment I. — Sugar and potassium chlorate are mixed, and a drop of sulfuric acid added.

Experiment II. — Sulfuric acid is added to syrup.

Experiment III. — A rubber ruler is electrified.

Experiment IV. — A beam of sunlight is decomposed with a prism.

Experiment V. — A piece of platinum wire is heated to redness.

Experiment VI. — A piece of magnesium wire is heated to redness.

Experiment VII. — Sulfur and potassium chlorate are mixed in a mortar with considerable friction.

Experiment VIII. — Solutions of potassium iodid and mercuric chlorid are mixed.

Experiment 9 and the succeeding experiments are to be performed by the pupil unless special directions to the contrary are given.

Experiment IX. A Chemical Change. — 1. Examine a piece of marble carefully, fix its appearance in mind, so that you can detect any change.

2. Drop a small piece in the test bottle and cover it with dilute hydrochloric acid. What occurs ?

3. After a short time test the gas in the upper part of the test bottle with a lighted match. Does the match continue to burn ? Is the gas combustible? Is the gas ordinary air? Why? Does the marble disappear '.'

4. In order to tell whether the marble has been changed chemically, the acid must be expelled. To accomplish this, pour the solution into an evaporating dish, place it on a piece of wire gauze, and bring the liquid to a boil. When the liquid begins to solidify and turn yellow, add a few drops of water, repeating, if necessary, to obtain a solid white residue.

Examine this residue, compare it carefully with marble. Set the residue aside for 24 hours to determine whether it is permanent when exposed to the air.

Fill out the following table : — Marble Residue

Is it hard or soft ?

Does it effervesce with hydrochloric acid ?

Is it sol ul »le in water ?

Is it permanent in air ?

How do the properties of the residue compare with those of marble ?

Is it marble ?

What have you proven ?

Experiment X. — Bring together on a flower-pot saucer a little phosphorus and iodin. What evidence have you that chemical action took place ? Have either of the original substances disappeared ? Has a new substance been formed ? It will be seen that simple contact is sufficient to cause the two substances to act upon each other.

CHEMICAL ACTION 5

Does either substance melt ? Why ?

Is this a case of chemical action between solids ?

Is the action as energetic at first as it is after a few seconds ? Explain.

Cautiox. — Handle phosphorus with great care ; it takes fire when rubbed or cut in the air, and should always be kept in water.

5. Conservation of Matter.

Experiment XL — Pour 10 cc. of dilute sulfuric acid into a beaker. In a second beaker pour an equal quantity of calcium chlorid solution. Place both beakers in one scale pan and balance them carefully with weights, sand, or shot, placed in the other scale pan. Now pour the calcium chlorid into the sulfuric acid. Does a chemical change occur ? Replace the beakers and determine whether the weight of the beakers and their contents has been changed. Does chemical action change the total quantity of matter in existence ? Was the total quantity of sulfuric acid in the world increased or diminished by the above experiment ? How was the total quantity of calcium chlorid affected ? of the white substance formed ?

6. The Effect of Solution on Chemical Action. Experiment XII. — Place as much baking soda as you can take on

the end of a knife blade in a dry test bottle. Add an equal amount of tartaric acid ; shake the bottle to mix the powders thoroughly. Has any change occurred ?

Pour a few cubic centimetres of water into the bottle. What evidence of chemical action do you observe ?

Does solution aid chemical action ? Is it because more intimate contact of the molecules is obtained when solutions are mixed than is possible with solids ? Should diminishing cohesion assist chemical action ? State your opinion as to why solution aids chemical action.

7. Effect of Heat on Chemical Action.

Experiment XIII. — 1. Mix six grammes of potassium chlorate and one gramme of powdered charcoal thoroughly. What occurs ?

2. Apply a lighted match. Was the change chemical or physical ?

How does the operation of striking a match illustrate the effect of heat upon chemical action ?

Why do metals rust more rapidly when hot than at lower temperatures ? Experiment 22 illustrates this effect. Do fuels combine with the air when cold ?

8. Light causes Chemical Action.

Experiment XIV. — Cat a design from tin-foil and place it on a piece of blue print paper. Expose paper and design to sunlight for a few minutes. Wash the paper in water.

Has the sunlight affected the exposed chemical ? In what way ?

The art of photography is based on the action of light on chemicals. In growing plants sunlight causes the decomposition of carbon dioxid, which is only accomplished by the chemist with difficulty.

In the preparation of hydrochloric acid by synthesis described on page 92, the chemical action is assisted by light.

Query. — Why do certain colors fade when exposed to light ?

9. Pressure. — When the two gases, hydrochloric acid and hydrogen phosphid, are subjected to increasing pressure they combine to form a crystalline solid known as phosphonium chlorid. Similarly sulfur and powdered lead may be caused to combine by great pressure, forming lead sulnd.

Quebt. — What relation does this action suggest between the intensities of chemical affinity and distances between molecules ?

10. Concussion or Detonation. — In a very few cases, chemical action is brought about by detonation. The molecules of the gas acetylene consist of two atoms of carbon united with two of hydrogen. If a small quantity of mercury fulminate be detonated near a globe filled with this gas the carbon is instantly deposited in solid form and the hydrogen liberated. This action is not fully understood; some chemists believe that the particular form of sound vibration produced disturbs the motions of the atoms constituting the molecule, and thus causes disruption.

11. Electricity. — If a current of electricity be jessed through a solution of copper sulfate, the compound is de-

CHEMICAL ACTION 7

composed, and many other compounds are affected in the same way. In Experiment 40 this effect is also illustrated.

12. The Effect of Trituration on Chemical Action. Experiment XV. — Using pincers, hold a small lump of rosin in the

Bunsen burner flame, observe the character of the flame produced by the burning rosin. Is rosin easily ignited ? Does it burn rapidly ? Does the rosin melt before it ignites ?

Experiment XVI. — Triturate a small piece of rosin in a mortar, fill the end of a large glass tube with the powder and blow it into the burner flame. Does the finely divided rosin burn with a smoky flame or does it flash ? Does it burn as rapidly as in the previous experiment ? How does the energy of the chemical action compare with that observed in the last experiment ? In which case is the higher temperature reached ?

Experiment XVII. — Make a compact pile of about \ cu. cm. of powdered rosin on a piece of porcelain or earthenware, ignite with a Bunsen burner. How does the chemical action compare with that of the previous experiment ? Does the increased chemical action depend upon the size of the particles ? Would a solid piece having the same area as the sum of the surfaces flash ? Does the chemical activity depend upon the surface only ? Upon the mass of the particles only ?

13. Mechanical Mixture.

Experiment XVIII. — 1. Mix about four grammes of sulfur and an equal weight of fine wrought iron filings on a sheet of paper. Divide into three portions.

2. Examine the first portion with a magnifying glass. Can you distinguish the particles of sulfur from those of iron ? Can you separate the iron from the sulfur with a magnet ? Now put the mixture in a test tube and pour water on it. Are the substances combined or not ? Shake the tube ; what is the yellow substance floating on the water ? Has chemical action taken place ?

3. Treat the second portion with carbon disulfid. What is the black substance at the bottom of the tube ? What has happened ? Is the color of the carbon disulfid changed ? What does this indicate ? Is a chemical compound formed in this experiment ?

Experiment XIX. — 1. Put the third portion of the mixture made in Experiment 18, in a dry test tube and heat gently. When it is red hot remove the tube from the flame. Is there any evidence of combustion in the tube ?

2. After the action is over and the tube has cooled down, loosen the contents with a short piece of wire, and pour it out on a piece of paper. Does the mass look like the mixture of sulfur and iron with which you started ?

3. Examine with a magnifying glass. Can you separate the sulfur and iron with water as before ? Can you separate them with a magnet ?

4. Treat a portion of the mass with carbon disulfid. Is the effect the same as before ? Is the color of the carbon disulfid changed ? What do you conclude concerning the effect of heat on the mixture ?

1. Define chemical action. What assists it ? What retards it ?

2. Mention those conditions which aid chemical action, (a) by decreasing the distance between the unlike molecules, (6) by diminishing the cohesion of the factors.

3. Describe an experiment to show that there is no loss of matter in chemical change.

4. Distinguish between a mechanical mixture and a chemical compound. Illustrate each.

5. Distinguish between chemistry and physics ; between atoms and molecules ; between chemical changes and physical changes.

6. What mechanical mixture was formed in Experiment 12 ? In what part of the experiment were chemical compounds formed ?

Write answers to these questions in your note-book.

Chapter II Symbols And Laws

14. Symbols. — Chemists of all countries have agreed to use the initial letter of the Latin name of an element as an abbreviation which shall stand for a single atom of that element. In case two or more elements begin with the same letter the second characteristic letter is added to the symbol, thus : —

C Carbon N Nitrogen Na* Sodium

Ca Calcium S Sulfur K* Potassium

CI Chlorin Si Silicon Ag Silver

Some writers use these symbols as mere shorthand signs for the full names of the elements. This usage is extremely objectionable; students who adopt it will not appreciate the important quantitative relations which are shown by reactions.

15. Formulae. — Compounds are represented by a formula or a group of symbols, showing the composition of the molecule of the substance.

Thus, the formula of sodium chlorid, NaCl, indicates that its molecule contains one atom of sodium and one of chlorin, and CaS represents a molecule of calcium sulfid which contains one atom of calcium and one of sulfur.

If a molecule contains more than one atom of a given

* The Latin name of sodium is Natrium, that of potassium is Kalium.

element, a subnumber is placed a little below and to the right of the symbol, and indicates the number of such atoms. Thus CaCL is the formula for calcium chlorid, which contains one atom of calcium and two of chlorin, and the formula for ferric oxid, FeX^, tells us that its molecule contains two atoms of iron and three of oxygen.

If more than one molecule of the substance is to be represented, the number is placed before the group of symbols. Thus 2 Ft '.,()., represents two molecules of ferric oxid containing four atoms of iron and six of oxygen.

In the absence of a coefficient a formula always represents a Bingle molecule.

16. The Law of Constant Proportions. — The law of definite proportions which has been called the corner stone of modern chemistry i> as follows: —

" Tin' same compound always contai)is the same elements combine I in the same fixed and defi n ite proportions"

The thousands of analyses which have been made of various compounds by chemists in all parts of the world, and which are now being made every day, are based upon this law. and in no single instance have the results obtained caused the truth of the law to be questioned.

17. Combining Weights. — Another important relation is to be learned from a study of the composition of various substances. Not only is the proportion by weight in which a certain element combines with a certain other element, to form a given compound, constant, but it is possible to select a number for each element, which shall represent the proportion by weight in which it unites with different elements.

The composition of the oxids mentioned thus far is given below : —

SYMBOLS AND LAWS

Mercury, 200 Oxygen, 16

Copper, 63.6 Oxygen, 16

Lead, 207 Oxygen, 16

Oxygen, 16

Iron, 5\S Oxygen, 16

In each of the above compounds it is observed that there are 16 parts by weight of oxygen, and this number or a simple multiple of it will express the proportion in which oxygen combines with any other element.

Such numbers have been carefully determined for all elements and are called combining weights.

18. The Law of Multiple Proportions. — The analysis of various substances further shows that a given element may combine with another in more than one proportion. For example, the elements nitrogen and oxygen form several compounds having the following composition : —

Nitrous oxid Nitric oxid .

Nitrous anhydrid Nitrogen peroxid Nitric anhydrid

28 parts 28 parts 28 parts 28 parts 28 parts

16 parts 32 parts 48 parts 04 parts 80 parts

It will be observed that while the quantity of nitrogen is the same in all the above compounds the quantity of oxygen varies, being twice as great in the second compound as in the first, three times as great in the third as in the first, etc. This series illustrates the law which applies to all cases in which more than one compound is formed from the same elements.

If two elements form more than one compound, the proportions by weight in which a given element combines with the other in each compound will be expressed either by its combining number or a simple multiple of its combining number.

19. The Atomic Theory. — The atomic theory was suggested by John Dalton, an English schoolmaster, early in this century, to account for the laws of definite and multiple proportions. It maintains —

1. That with a few possible exceptions all molecules are made up of smaller particles.

2. That these particles are indivisible (they are therefore called atoms).

.°). That all atoms of a given element are equal in size and weight

4. That atoms of different substances have different weigh is.

5. That the combining weights of the elements are simply the relative weights of the atoms, and may therefore be called the atomic weights.

The explanation of the facts of chemistry which this theory offers is so satisfactory that it is universally accepted.

20. Atomic Weights. — As hydrogen enters into combination in smaller proportion than any other element, its combining weight or atomic weight is taken as the unit. When we say that the atomic weight of oxygen is 16, we mean simply that the atoms of oxygen are sixteen times heavier than those of hydrogen. The exact weight of an atom of hydrogen has never been determined but it is called a microcrith. The atom of oxygen weighs 16 microcriths.

The following table gives the exact values of the atomic weights of the elements referred to in this book. The standard is Oxygen = 16.

SYMBOLS AND LAWS Table of Atomic Weights

Xe.me

Sym.

Xatue

Sym .

Aluminum . . . Al

27.11

Antimony . . .

Sb

120.42

Argon .

A

Arsenic

As

75.01

Barium .

Ba

137.43

Bismuth

Bi

208.11

Boron

B

10.95

Bromin . .

Br

79.95

Cadmium

Cd

111.95

Calcium

Ca

40.07

Carbon .

C

Chromium .

Cr

52.14

Chlorin .

CI

35.45

Copper . .

Cu

63.60

Cobalt .

Co

58.93

Gold . , .

Au

197.23

Fluorin .

F

19.06

Iodin . .

I

126.85

H

1.008

Lead . .

Pb

206.92

Iron . .

Fe

56.02

Magnesium

Mg

24.28

Lithium .

Li

7.03

Mercury .

Hg

200.00

Manganese

Mn

54.99

Nitrogen .

N

14.04

Nickel .

Ni

58.69

Phosphorus

P

31.02

Oxygen .

16.00

Potassium .

K

39.11

Platinum

Pt

194.89

Silver . .

Ag

107.92

Silicon .

Si

28.40

Strontium .

Sr

87.61

Sodium .

Na

23.05

Tin . . .

Sn

119.0

Sulfur .

S

32.0

Zinc . . .

Zn

65.41

21. Reaction. — The force which is exerted between atoms is called chemical affinity. The affinity of a given atom for other atoms varies greatly, often being very strong for certain kinds of atoms and feeble for others. If, when any substances are mixed, a rearrangement of the atoms would produce more stable compounds, i.e. if the force which holds the atoms together in the new compounds is stronger than that which bound them in their original form, such rearrangement will take place. The process of redistribution of the atoms in the molecules concerned in the phenomenon is called chemical action or reaction.

A reaction is due to chemical affinity and causes a chemical change.

Substances used to bring about desired reactions are called reagents.

The substances which, go into a reaction are called factors, and those which come from a reaction products.

Reactions are ordinarily expressed by equations in which the symbols and formulae of the factors are placed on the left of the sign of equality, and those of the products on the right. The algebraic signs plus and minus are used in the ordinary sense in the equations.

The fact that atoms can neither be created nor destroyed, even by chemical means, justifies the use of the sign of equality to connect factors and products, and it should never be placed until the student has "satisfied the reaction," i.e. has determined that there are exactly as many atoms of each element in the products as there are in the factors.

Illustration. In Experiment 11 the following reaction

occurred : —

This should be read as follows : one molecule of calcium chlorid plus one molecule of sulfuric acid forms one molecule of calcium sulfate plus two molecules of hydrochloric acid.

The chemical change occurring in Experiment 19 may be expressed as follows : —

Fe + S = FeS.

Such equations express very concisely the relations between the atoms and molecules in the chemical changes which they represent, and every chemical change which is clearly understood may be expressed in this way. Equations are also useful because of the important quantitative relations between masses which are made evident when we consider the atomic weights of the elements represented.

SYMBOLS AND LAWS 15

In the equation given above, the symbol Fe not only signifies an atom of iron, but it also stands for 56 parts of iron, by weight, and the symbol S stands for 32 parts of sulfur by weight. We fchug have a mathematical expression which shows the relation between the masses of iron and sulfur which take part in the chemical change.

Fe + S = FeS 5G 32 88

The equation can now be read : —

56 parts of iron unite with 32 parts of sulfur to form 88 parts of ferrous sulfid. The solution of many chemical problems depends upon this use of equations. (See Chapter IX.)

22. Analysis, Synthesis, and Metathesis. — All chemical changes may be referred to one of four classes : —

(«) Compound molecules may be separated into their elements, or into simpler groups of elements, as, for example, mercury rust is separated into mercury and oxygen in Experiment 25, or as potassium chlorate KCIO3, is decomposed in Experiment 29, forming potassium chlorid KC1, and oxygen. Such changes are analytic, and the process which brings them about is known as analysis.

(b) Compound molecules may be formed by direct union of elements, or simpler groups of elements, as when phosphorus combined with iodin, in Experiment 10, forming phosphorous di-iodid PI 2 , or when carbon monoxid CO, combines with oxygen to form carbon dioxid CO2. (See Experiment 96.) Such changes are synthetic, and the process is known as synthesis.

(c) Compound molecules may be formed by a change involving both analysis and synthesis, which is known as metathesis, or double decomposition. In such processes an exchange of atoms, or groups of atoms, takes place between two compound molecules, as when a solution of sodium sulfate Na 2 S0 4 , and barium chlorid BaCl 2 , are mixed. Each substance is decomposed, and the atoms combine to form two new substances, barium sulfate BaSO*, and sodium chlorid NaCl.

(d) In some cases new substances are formed without changing either the kinds of atoms, or the number of atoms of each kind, in the molecule. For example, when a solution of ammonium cyanate XH 4 . O . CN, is heated it is transformed into urea X 2 H 4 CO, a substance having entirely different chemical and physical properties. It will be observed that these molecules contain the same number of atoms of each element ; we have excellent evidence, however, that the first one contains cyanogen CX, while the second contains carbon monoxid CO.

1. How many atoms of hydrogen in 6 H2SO4 ? of sulfur ? of oxygen ?

2. How many atoms of each element are represented by the following formula? : 2 ZnCl 2 , 3 HX0 3 , 5 H 2 0, 14 XH 3 .

3. How many molecules of each substance are represented by above formula? ?

4. Define chemical affinity, reaction, reagent, factor, product.

5. Distinguish between atoms and molecules. Does a chemical affinity exist between molecules ? Give a reason for your answer.

6. What is atomic weight ? How is atomic weight related to specific gravity ?

7. What element is selected as the standard of atomic weight ? Why is this element selected ?

8. State the atomic theory.

9. State'five principles observed in writing chemical symbols and formulae.

10. What is a chemical equation ? What is meant by the combining weight of an element ?

11. State the law of constant proportions. Of multiple proportions.

12. State five principles to be observed in writing chemical equations.

Chapter III Chemistry Of The Air

23. The Formation of Rust.

Experiment XX. — 1. In a small porcelain crucible or a clay pipe bowl put a small piece of lead or zinc. Heat with laboratory burner and notice the changes that take place. Do not allow the containing vessel to become too hot, for liquefie ,1 rust will be absorbed. After the lead begins to melt, stir with a thick iron wire. Observe carefully what forms on the surface of the metal. Does the lead retain its bright mirror-like surface if not stirred ? Continue to heat and stir until the substance is changed to a powder. What is its appearance now ?

2. Let it cool. Is it lead ? What difference is there between the action in this case and in nielting ice and cooling the water again ? Which is chemical and which is physical action ? Why ? Was the change just observed produced by the heat or by the action of the air ? In order to answer this question let us repeat the experiment, preventing any action of the air by covering the metal with a film of melted rosin.

Experiment XXL — Repeat Experiment 20, adding as much powdered rosin as can be lifted on the blade of a penknife. Do not stir the metal. Does it rust or does the surface remain bright and mirror-like ? Is it changed to powder ? How do you explain the difference in result of this experiment and the last ? What do you conclude concerning the cause of the change produced in the previous experiment ? Is the action due to the high temperature or to the action of the air or to both ? Does lead rust more rapidly at high than at low temperature ? Rosin is used to prevent rusting of hot metals in process of soldering.

24. Effects of Air on Iron at Ordinary and at High Temperatures.

Experiment XXII. — Wind a piece of No. 30 iron wire about a foot

long around the finger and heat the loops thus formed in the tip of a

laboratory burner flame for a minute or two. Holding the loop over

a sheet of paper, straighten the wire. Compare the scale which drops off with the rust formed < n iron at ordinary temperatures. Is it the same color? Does iron rust more rapidly at high or low temperatures ? I low do you know ? Has a chemical change occurred ? Pass a magnet over a mass of red rust ; of black rust. Are they magnetic ? (See paragraph on Oxid.s in Nature, page 35.)

25. Various Ways of Protecting Iron.

Several years ago Professor Barff, of London, suggested that iron might be protected from the action of the air by exposing it to superheated steam at high temperature, thus forming a coating of black rust on its surface. The process has been somewhat modified, and is now known as the Bower-Barif process. It is quite extensively employed as a finish for iron ornaments, and has been used in certain cities to protect water pipes.