61. Deposition of Lead.
Experiment 37. - Perform this experiment in the same manner as the
two previous ones, dissolving a small piece of Pb, and using a
strip of Zn to precipitate the Pb. 3 Pb + 8 HNO3 - 3 Pb (NO4)2 +
4 Ha0 + 2 NO. Pb (NO3) 2 + Zn = ? h.
62. Explanation. -These experiments show that Cu will replace Ag
in a solution of AgNO3, that Pb will replace and deposit Cu from
a similar compound, and that Zn will deposit Pb in the same way.
They show that the affinity of Zn for (NO3) is stronger than
either Ag, Cu, or Pb. We. express this affinity by saying that Zn
is the most positive of the four metals, while Ag is the most
nega- tive. Cu is positive to Ag, but negative to Pb and Zn.
Which of the four elements are positive to Pb, and which
negative? Mg would withdraw Zn from a similar solution, and be in
its turn withdrawn by Na. The table on page 43 is founded on this
relation. A given element is positive to every element above it
in the list, and negative to all below it.
Metals are usually classed as positive, non-metals as negative.
Each in union with O and 1=I gives rise to a very important class
of compounds,= - the negative to acids, the positive to bases.
In the following, note whether the positive or the negative
element is written first: - HCl, Na20,-As2S3, -MgBr2, Ag2S. Na2SO4
is made up of two parts, Na2 being positive, the radical SO4
negative. Like elements, radicals are either positive or
negative. In the following, separate the positive element from
the negative radical by a vertical line: Na2CO3, NaNO3, ZnSO4,
The most common positive radical is NH4, ammonium, as in NH4Cl.
It always deports itself as a metal. The commonest radical is the
negative OH, called hydroxyl, from hydrogen- oxygen. Take away H
from the symbol of water, H-O-H, and hydroxyl - (OH) with one
free bond is left. If an element takes the place of H, i.e.
unites with OH, the compound is called a hydrate. KOH is
potassium hydrate. Name NaOH, Ca(OH)2, NH4OH, Zn(OH)2, Al2(OH)6.
Is the first part of each symbol above positive or negative?
H has an intermediate place in the list. It is a constituent of
both acids and bases, and of the neutral substance, water.
Negative or Non-Metallic Elements.
Acid-forming with H(usually OH).
Positive or Metallic Elements.
Base-forming with OH.
The following experiment is to be performed only by the teacher,
but pupils should make drawings and explain.
63. Decomposition of Water.
Experiment 38. - Arrange "in series" two or more cells of a Bunsen
battery (Physics, page 164), [References are made in this book to
Gage's Introduction to Physical Science.] and attach the terminal
wires to an electrolytic apparatus (Fig. 19) filled with water
made slightly acid with H2SO4. Construct a diagram of the
apparatus, marking the Zn in the liquid +, since it is positive,
and the C, or other element, -. Mark the electrode attached to
the Zn -, and that attached to the C +; positive electricity at
one end of a body commonly implies negative at the other.
Opposites attract, while like electricities repel each other.
These analogies will aid the memory. At the + electrode is the -
element of H2O, and at the - electrode the + element. Note, page
43, whether H or O is positive with reference to the other, and
write the symbol for each at the proper electrode. Compare the
diagram with the apparatus, to verify your conclusion. Why does
gas collect twice as fast at one electrode as at the other? What
does this prove of the composition of water? When filled, test
the gases in each tube, for O and H, with a burning stick.
Electrical analysis is called electrolysis.
If a solution of NaCl be electrolyzed, which element will go to
the + pole? Which, if the salt were K2SO4? Explain these
reactions in the electrolysis of that salt. K2SO4 = K2 + S03 + O.
SO4 is unstable, and breaks up into SO3 and O. Both K and SO3
have great affinity for water. K2 + 2 H2O = 2 KOH + H2. S03 + H2O
The base KOH would be found at the - electrode, and the acid
H2SO4 at the + electrode.
The positive portion, K, uniting with H2O forms a base; the
negative part, S03, with H2O forms an acid. Of what does this
show a salt to be composed?
64. Conclusions. - These experiments show (1) that at the +
electrode there always appears the negative element, or radical,
of the compound, and at the - electrode the positive element; (2)
that these elements unite with those of water, to make, in the
former case, acids, in the latter, bases; (3) that acids and
bases differ as negative and positive elements differ, each being
united with O and H, and yet producing compounds of a directly
opposite character; (4) that salts are really compounded of acids
and bases. This explains why salts are usually inactive and
neutral in character, while acids and bases are active agents.
Thus we see why the most positive or the most negative elements
in general have the strongest affinities, while those
intermediate in the list are inactive, and have weak affinities;
why alloys of the metals are weak compounds; why a neutral
substance, like water, has such a weak affinity for the salts
which it holds in solution; and why an aqueous solution is
regarded as a mechanical mixture rather than a chemical compound.
In this view, the division line between chemistry and physics is
not a distinct one. These will be better understood after
studying the chapters on acids, bases and salts.
UNION BY VOLUME.
66. Avogadro's Law of Gases. - Equal volumes of all gases, the
temperature and pressure being the same, have the same number of
molecules. This law is the foundation of modern chemistry. A
cubic centimeter of O has as many molecules as a cubic centimeter
of H, a liter of N the same number as a liter of steam, under
similar conditions. Compare the number of molecules in 5 l. of
N2O with that in 10 l. Cl. 7 cc. vapor of I to 6 cc. vapor of S.
The half-molecules of two gases have, of course, the same
relation to each other, and in elements the half-molecule is
usually the atom.
The molecular volumes - molecules and the surrounding space - of
all gases must therefore be equal, as must the half-volumes.
Notice that this law applies only to gases, not to liquids or
solids. Let us apply it to the experiment for the electrolysis of
water. In this we found twice as much H by volume as O.
Evidently, then, steam has twice as many molecules of H as of O,
and twice as many half-molecules, or atoms. If the molecule has
one atom of O, it must have two of H, and the formula will be
Suppose we reverse the process and synthesize steam, which can be
done by passing an electric spark through a mixture of H and O in
a eudiometer over mercury; we should need to take twice as much H
as O. Now when 2 cc. of H combine thus with 1 cc. of O, only 2
cc.of steam are produced. Three volumes are condensed into two
volumes, and of course three molecular volumes into two, three
atomic volumes into two. This may be written as follows: -
H + H + O = H2O.
This is a condensation of one-third.
If 2 l. of chlorhydric acid gas be analyzed, there will result 1
l. of H and 1 l. of Cl. The same relation exists between the
molecules and the atoms, and the reaction is: -
HCl = H + Cl.
Reverse the process, and 1 l. of H unites with 1 l. of Cl to
produce 2 l. of the acid gas; there is no condensation, and the
symbol is HCl. In seven volumes HCl how many of each constituent?
The combination of two volumes of H with one volume of S is found
to produce two volumes of hydrogen sulphide. Therefore two atoms
of H combine with one of S to form a molecule whose symbol is
H + H + S = H2S.
What is the condensation in this case?
(1) How many liters of S will it take to unite with 4 l. of H?
How much H2S will be formed?
(2) How many liters of H will it take to combine with 5 l. of S?
How much H2S results?
(3) In 6 l. H2S how many liters H, and how much S? Prove.
(4) In four volumes H2S how many volumes of each constituent?
(5) If three volumes of H be mixed with two volumes of S, so as
to make H2S, how much will be formed? How much of either element
will be left? An analysis of 2 cc. of ammonia gives 1 cc. N and 3
cc. H. The symbol must then be NH3, the reaction, -
NH3 = N + H + H + H.
What condensation in the synthesis of NH3?
In 12 cc. NH3 how many cubic centimeters of each element? In 2
1/2 cc? How much H by volume is required to combine with nine
volumes of N? How many volumes of NH3 are produced?
In elements that have not been weighed in the gaseous state, as
C, the evidence of atomic volume is not direct, but we will
assume it. Thus two volumes of marsh gas would separate into one
of C and four of H. What is its symbol and supposed condensation?
Two volumes of alcohol vapor resolve into two of C, six of H, and
one of O. What is its symbol? its condensation?
The symbol itself of a compound will usually show what its
condensation is; e.g. HCl, HBr, HF, etc., have two atoms; hence
there will be no shrinkage. In H2O, SO2, CO2, the molecule has
three atoms condensed into the space of two, or one-third
shrinkage. In NH3 four volumes are crowded into the space of two,
a condensation of one-half.
P, As, Hg, Zn, have exceptional atomic volumes.
ACIDS AND BASES.
66. What Acids Are.
Experiment 39. - Pour a few drops of chlorhydric acid, HCl, into a
clean evaporating-dish. Add 5 cc. H2O, and stir. Touch a drop to
the tongue, noting the taste. Dip into it the end of a piece of
blue litmus paper, and record the result. Thoroughly wash the
dish, then pour in a few drops of nitric acid, HNO3, and 5 cc.
H2O, and stir. Taste, and test with blue litmus. Test in the same
way sulphuric acid, H2SO4. Name two characteristics of an acid.
In a vertical line write the formulae of the acids above. What
element is common to them all? Is the rest of the formula
positive or negative?
67. An Acid is a substance composed of H and a negative element
or radical. It has usually a sour taste, and turns blue litmus
red. Litmus is a vegetable extract obtained from lichens in
Southern Europe. Acids have the same action on many other
vegetable pigments. Are the following acid formulae, and why?
H2SO3, HBr, HNO2, H3PO3, H4SiO4. Most acids have O as well as H.
Complete the symbols for acids in the following list, and name
them, from the type given: -
HCl, chlorhydric acid. HN03, nitric acid.
?Br, ? ?Cl? ?
?I, ? ?Br? ?
?F, ? ?I? ?
H3PO4, phosphoric acid. H3PO3, phosphorous acid.
?As? ? ?As? ?
Complete these equations: -
H2SO3 - H2O = ? | 2 HN03 - H2O = ?
H2SO4 - H2O = ? | 2 HNO2 - H2O = ?
H2CO3 - H2O = ? | 2 H3AsO4 - 3 H2O = ?
Are the products in each case metallic or non-metallic oxides?
They are called anhydrides. Notice that each is formed by the
withdrawal of water from an acid. Reverse the equations; as, SO3
+ H2O = ?
68. An Anhydride is what remains after water has been removed
from an acid; or, it is the oxide of a non- metallic element,
which, united with water, forms an acid. SO2 is sulphurous
anhydride, SO2 sulphuric anhydride, the ending ic meaning more O,
or negative element, than ous. Name the others above.
Anhydrides were formerly called acids, - anhydrous acids, in
distinction from hydrated ones, as CO2 even now is often called
Experiment 40. - Hold a piece of wet blue litmus paper in the
fumes of SO2, and note the acid test. Try the same with dry
Experiment 41. - Burn a little S in a receiver of air containing
10 cc. H2O, and loosely covered, as in the O experiment. Then
shake to dissolve the SO2. H2O + SO2 = H2SO3. Apply test paper.
69. Naming Acids. - Compare formulae H2SO3 and H2SO4. Of two acids
having the same elements, the name of the one with least O, or
negative element, ends in ous, the other in ic. H2SO3 is
sulphurous acid, H2SO4, sulphuric acid. Name H3PO4 and H3PO3;
H3AsO3 and H3ASO4; HNO2 and HNO3.
If there are more than two acids in a series, the prefixes hypo,
less, and per, more, are used. The following is such a series:
HClO, HClO2, HClO3, HClO4.
HClO3 is chloric acid; HClO2, chlorous; HClO, hypochlorous; HClO4
perchloric. Hypo means less of the negative element than ous; per
means more of the negative element than ic. Name: H3PO4 (ic),
H3PO3, H3PO2. Also HBrO (HBrO2 does not exist), HBrO3 (ic),
What are the three most negative elements? Note their occurrence
in the three strongest and most common acids. Hereafter note the
names and symbols of all the acids you see.
70. What Bases Are.
Experiment 42. - Put a few drops of NH4OH into an evaporating-
dish. Add 5 cc. H2O, and stir. Taste a drop. Dip into it a piece
of red litmus paper, noting the effect. Cleanse the dish, and
treat in the same way a few drops NaOH solution, recording the
result. Do the same with KOH. Acid stains on the clothing, with
the exception of those made by HNO3, maybe removed by NH4OH.
H2SO4, however, rapidly destroys the fiber of the cloth.
Name two characteristics of a base. In the formulae of those
bases, what two common elements? Name the radical. Compare those
symbols with the symbol for water, HOH. Is (OH) positive or
negative? Is the other part of each formula positive or negative?
What are two constituents, then, of a base? Bases are called
hydrates. Write in a vertical line five positive elements. Note
the valence of each, and complete the formula for its base. Affix
the names. Can you see any reason why the three bases above given
are the strongest?
Taking the valences of Cr and Fe, write symbols for two sets of
hydrates, and name them. Try to recognize and name every base
hereafter met with.
A Base is a substance which is composed of a metal, or positive
radical, and OH. It generally turns red litmus blue, and often
has an acrid taste.
An Alkali is a base which is readily soluble in water. The three
principal alkalies are NH4OH, KOH, and NaOH.
Alkali Metals are those which form alkalies. Name three.
An Alkaline Reaction is the turning of red litmus blue.
An Acid Reaction is the turning of blue litmus red.
Experiment 43. - Pour 5 cc. of a solution of litmus in water, into
a clean t.t. or small beaker. Pour 2 or 3 cc. of HCl into an
evaporating-dish, and the same quantity of NH4OH into another
dish. Take a drop of the HCl on a stirring-rod and stir the
litmus solution with it. Note the acid reaction. Clean the rod,
and with it take a drop (or more if necessary) of NH4OH, and add
this to the red litmus solution, noting the alkaline reaction.
Experiment in the same way with the two other principal acids and
the two other alkalies.
Litmus paper is commonly used to test these reactions, and
hereafter whenever the term LITMUS is employed in that sense, the
test-paper should be understood. This paper can be prepared by
dipping unglazed paper into a strong aqueous solution of
71. Acids and Bases are usually Opposite in Character. - When two
forces act in opposition they tend to neutralize each other. We
may see an analogy to this in the union of the two opposite
classes of compounds, acids and bases, to form salts.
Experiment 44. - Put into an evaporating-dish 5 cc. of NaOH
solution. Add HCl to this from a t.t., a few drops at a time,
stirring the mixture with a glass rod (Fig. 20), and testing it
with litmus paper, until the liquid is neutral, i.e. will not
turn the test paper from blue to red, or red to blue. Test with
both colors. If it turns blue to red, too much acid has been
added; if red to blue, too much base. When it is very nearly
neutral, add the reagent, HCl or NaOH, a drop at a time with the
stirring-rod. It must be absolutely neutral to both colors.
Evaporate the water by heating the dish over asbestus paper, wire
gauze, or sand, in an iron plate (Fig. 21) till the residue
becomes dry and white. Cool the residue, taste, and name it. The
equation is: HCl + NaOH = NaCl + HOH or H2O. Note which elements,
positive or negative, change places. Why was the liquid boiled?
The residue is a type of a large class of compounds, called
(Fig. 20) (Fig. 21)
Experiment 45. - Experiment in the same way with KOH solution
and H2SO4, applying the same tests. H2SO4 + 2 KOH = K2SO4 + 2
HOH. What is the solid product?
Experiment 46. - Neutralize NH4OH with HNO3, evaporate, apply the
tests, and write the equation. Write equations for the
combination of NaOH and H2SO4; NaOH and HNO3; KOH and HCl; KOH
and HNO3; NH4OH and HCl; NH4OH and H2SO4. Describe the experiment
represented by each equation, and be sure you can perform it if
asked to do so. What is the usual action of a salt on litmus? How
is a salt made? What else is formed at the same time? Have all
salts a saline taste? Does every salt contain a positive element
or radical? A negative?
73. A Salt is the product of the union of a positive and a
negative element or radical; it may be made by mixing a base and
The salt KI represents what acid? What base, or hydrate? Write
the equation for making KI from its acid and base. Describe the
experiment in full. Classify, as to acids, bases, or salts: KBr,
Fe(OH)2, HI, NaBr, HNO2, Al2(OH)6, KClO3, HClO3, H2S, K2S, H2S03,
K2SO4, Ca(OH)2, CaCO3, NaBr03, CaSO4, H2CO3, K2CO3, Cu(OH)2,
Cu(NO3)2, PbSO4, H3P04, Na2P04. In the SALTS above, draw a light
vertical line, separating the positive from the negative part of
the symbol. Now state what acid each represents. What base. Write
the reaction in the preparation of each salt above from its acid
and base; then state the experiment for producing it.
74. Naming Salts. - (NO3) is the nitrate radical; KNO3 is
potassium nitrate. From what acid? (NO2) is the nitrite radical;
KN02 is potassium nitrite. From what acid? Note that the endings
of the acids are OUS and IC; also that the names of their salts
end in ITE and ATE. From which acid - IC or OUS - is the salt
ending in ATE derived? That ending in ITE?
Name these salts, the acids from which they are derived, and the
endings of both acids and salts: NaNO3, NaNO2, K2SO4, K2SO3,
CaSO4, CaSO3, KClO3, KClO2, KClO, KClO4 (use prefixes HYPO and
PER, as with acids), Ca3(PO4)2, Ca3(P03)2, CuSO4, CuSO3, AgNO3,
Cu(NO3)2. FeS, FeS2, are respectively FERROUS SULPHIDE and FERRIC
SULPHIDE. Name: HgCl, HgCl2, FeCl2, Fe2Cl6, FeSO4, Fe2(SO4)3.75.
Acid Salts. - Write symbols for nitric, sulphuric, phosphoric
acids. How many H atoms in each? Replace all the H in the symbol
of each with Na, and name the products. Again, in sulphuric acid
replace one atom of H with Na; then in phosphoric replace first
one, then two, and finally three H atoms with Na. HNaSO4 is
hydrogen sodium sulphate; HNa2P04 is hydrogen di-sodium
phosphate. Name the other salts symbolized. Name HNaNH4P04.
Though these products are all salts, some contain replaceable H,
and are called acid salts. Those which have all the H replaced by
a metal are normal salts. Name and classify, as to normal or acid
salts: Na2CO3, HNaCO3, K2SO4, HKSO4, (NH4)2SO4, HNH4SO4, Na3P04,
The BASICITY of an acid is determined by the number of
replaceable H atoms in its molecule. It is called MONOBASIC if it
has one; DIBASIC if two; TRI- if three, etc. Note the basicity of
each acid named above. How many possible salts of H2SO4 with Na?
Of H3P04 with Na? Which are normal and which acid? What is the
basicity of H4Si04?
Some normal, as well as acid, salts change litmus. Na2CO3,
representing a strong base and a weak acid, turns it blue. There
are other modes of obtaining salts, but this is the only one
which we sball consider.
76. Salts Occur Abundantly in Nature, such as NaCl, MgSO4, CaCO3.
Acids and bases are found in small quantities only. Why is this?
Why are there not springs of H2SO4 and NH4OH? We have seen that
acids and bases are extremely active, have opposite characters,
and combine to form relatively inactive salts. If they existed in
the free state, they would soon combine by reason of their strong
affinities. This is what in all ages of the world has taken
place, and this is why salts are common, acids and bases rare.
Active agents rarely exist in the free state in large quantities.
Oxygen seems to be an exception, but this is because there is a
superabundance of it. While vast quantities are locked up in
compounds in rocks, water, and salts of the earth, much remains
with which there is nothing to combine.
77. We have seen that salts are made by the union of acids and
bases. Can these last be obtained from salts?
78. Preparation of HCl.
Experiment 47. - Into a flask put 10 g. coarse NaCl, and add 20
cc. H2SO4. Connect with Woulff bottles [Woulff bottles may be
made by fitting to wide-mouthed bottles corks with three holes,
through which pass two delivery tubes, and a central safety tube
dipping into the liquid, as in Figures 22 and 23.] partly filled
with water, as in Figure 22. One bottle is enough to collect the
HCl; but in that case it is less pure, since some H2SO4 and other
impurities are carried over. Several may be connected, as in
Figure 23. The water in the first bottle must be nearly saturated
before much gas will pass into the second. Heat the mixture 15 or
20 minutes, not very strongly, to prevent too much foaming.
Notice any current in the first bottle. NaCl + H2SO4 = HNaSO4 +
HCl. Intense heat would have given: 2NaCl + H2SO4 = Na2SO4 +
2HCl. Compare these equations with those for HNO3. In which
equation above is H2SO4 used most economically? Both reactions
take place when HCl is made on the large scale.
79. Tests. Experiment 48. - (1) Test with litmus the liquid in
each Woulffbottle. (2) Put a piece of Zn into a t.t. and cover it
with liquid from the first bottle. Write the reaction, and test
the gas. (3) To 2 cc.solution AgNO3 in a t.t. add 2 cc.of the
acid. Describe, and write the reaction. Is AgCl soluble in water?
(4) Into a t.t. pour 5 cc.Pb(NO3)2 solution, and add the same
amount of prepared acid. Give the description and the reaction.
(5) In the same way test the acid with Hg2(NO3)2 solution, giving
the reaction. (6) Drake a little HCl in a t.t., and bring the gas
escaping from the d.t. in contact with a burning stick. Does it
support the combustion of C? (7) Hold a piece of dry litmus paper
against it. [figure 23] (8) Hold it over 2 cc.of NH4OH in an
evaporating-dish. Describe, name the product, and write the
reaction. (3), (4), (5), (8), are characteristic tests for this
80. Chlorhydric, Hydrochloric or Muriatic, Acid is a Gas. - As
used, it is dissolved, in water, for which it has great affinity.
Water will hold, according to temperature, from 400 to 500 times
its volume of HCl. Hundreds of thousands of tons of the acid are
annually made, mostly in Europe, as a bye-product in Na2CO3
manufacture. The gas is passed into towers through which a spray
of water falls; this absorbs it. The yellow color in most
commercial HCl indicates impurities, some of which are Fe, S, As,
and organic matter. As, S, etc., come from the pyrites used in
making H2SO4. Chemically pure (C.P.) acid is freed from these,
and is without color. The gas may be dried by passing it through
a glass tube holding CaCl2 (Fig. 16) and collecting it over
The muriatic acid of commerce consists of about two- thirds water
by weight. HCl can also be made by direct union of its
constituents.81. Uses. - HCl is used to make Cl, and also
bleaching- powder. Its use as a reagent in the laboratory is
illustrated by the following experiment: - Experiment 49. - Put
into a t.t. 2 cc. AgNO3 solution, add 5 cc. H2O, then add slowly
HCl so long as a ppt. (precipitate) is formed. This ppt. is AgCl.
Now in another t.t. put 2 cc. Cu(NO3)2, solution, add 5 cc. H2O,
then a little HCl. No ppt. is formed. Now if a solution of AgNO3
and a solution of Cu(NO3)2 were mixed, and HCl added, it is
evident that the silver would be precipitated as chloride of
silver, while the copper would remain in solution. If now this be
filtered, the silver will remain on the filter paper, while in