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List Of Contents | Contents of An Introduction to Chemical Science
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--

Zinc + hydrogen sulphate = zinc sulphate + hydrogen.

Zn + H2SO4 = ZnSO4 + 2H.

Iron might have been used instead of zinc, in which case the
reactions would have been:--

Iron + hydrogen chloride = iron chloride + hydrogen.

Fe + 2 HCl = FeCl2 + 2 H.

Iron + hydrogen sulphate = iron sulphate + hydrogen.

Fe + H2SO4 = FeSO4 + 2 H.

Write the weights and explain the equations. The latter should be
memorized.

33. Properties.

Experiment 21.--Lift with the left hand a receiver of H, still
inverted, and insert a burning splinter with the right (Fig. 12).
Does the splinter continue to burn? Does the gas burn?  If so,
where?  Is the light brilliant? Note the color of the flame. Is
there any explosion? Try this experiment with several receivers.
Is the gas a supporter of combustion? i.e. will carbon burn in
it? Is it combustible? i.e. does it burn?  If so, it unites with
some part of the air. With what part?34. Collecting H by Upward
Displacement.

Experiment 22.--Pass a d.t. from a H generator to the top of a
receiver or t.t. (Fig. 13). The escaping H being so much lighter
than air will force the latter down. To obtain the gas unmixed
with air, the d.t. should tightly fit a cardboard placed under
the mouth of the receiver. When filled, the receiver can be
removed, inverted as usual, and the gas tested. In this and other
experiments for generating H, a thistle-tube, the end of which
dips under the liquid, can be used for pouring in acid, as in
Figure 13.

35. Philosopher's Lamp and Musical Flame.

Experiment 23.--Fit to a cork a piece of glass tubing 10 or 15
cm. long, having the outer end drawn out to a point with a small
opening, and insert it in the H generator. Before igniting the
gas at the end of the tube take the, precaution to collect a t.t.
of it by upward displacement, and bring this in contact with a
flame. If a sharp explosion ensues, air is not wholly expelled
from the generator, and it would be dangerous to light the gas.
When no sound, or very little, follows, light the escaping gas.
The generation of H must not be too rapid, neither should the
t.t. be held under the face, as the cork is liable to be forced
out by the pressure of H. A safety-tube, similar to the thistle-
tube above, will prevent this. This apparatus is called the
"philosopher's lamp."  Thrust the flame into a long glass tube 1-
1/2 to 3 cm. in diameter, as shown in Figure 14, and listen for a
musical note.

36. Product of Burning H in Air.

Experiment 24.--Fill a tube 2 or 3 cm. in diameter with calcium
chloride, CaCl2, and connect one end with a generator of H (Fig.
15). At the other end have a philosopher's lamp-tube.Observing
the usual precautions, light the gas and hold over it a receiver,
till quite a quantity of moisture collects. All water was taken
from the gas by the dryer, CaCl2. What is, therefore, the product
of burning H in air? Complete this equation and explain it: 2H +
O = ? Figure 16 shows a drying apparatus arranged to hold CaCl2.

[Fig. 15][Fig. 16]

37. Explosiveness of H.

Experiment 25. -- Fill a soda-water bottle of thick glass with
water, invert it in a pneumatic trough, and collect not over 1/4
full of H. Now remove the bottle, still inverted, letting air in
to fill the other 3/4. Mix the air and H by covering the mouth of
the bottle with the hand, and shaking well; then hold the mouth
of the bottle, slightly inclined, in a flame. Explain the
explosion which follows. If 3/4 was air, what part was O? What
use did the N serve? Note any danger in exploding H mixed with
pure O. What proportions of O and H by volume would be most
dangerously explosive? What proportion by weight?

By the rapid union of the two elements, the high temperature
suddenly expanded the gaseous product, which immediately
contracted; both expansion and contraction produced the noise of
explosion.

38. Pure H Is a Gas without Color, Odor, or Taste.

--It is the lightest of the elements, 14 1/2 times as light
asair. It occurs uncombined in coal-mines, and some other places,
but the readiness with which it unites with other elements,
particularly O, prevents its accumulation in large quantities. It
constitutes two-thirds of the volume of the gases resulting from
the decomposition of water, and one-ninth of the weight. Compute
the latter from its symbol. It is a constituent of plants and
animals, and some rocks. Considering the volume of the ocean, the
total amount of H is large. It can be separated from H2O by
electrolysis, or by C, as in the manufacture of water gas.

When burned with O it forms H2O. Pure O and H when burning give
great heat, but little light. The oxy-hydrogen blow-pipe (Fig.
17) is a device for producing the highest temperatures of
combustion. It has O in the inner tube and H in the outer. Why
would it not be better the other way? These unite at the end, and
are burned, giving great heat. A piece of lime put into the flame
gives the brilliant Drummond or calcium light.

Chapter IX. UNION BY WEIGHT.

39. In the Equation --

Zn + 2 HCl = ZnCl2 + 2 H
65 + 73    = 136   + 2

65 parts by weight of Zn are required to liberate 2 parts by weight of
H; or, by using 65 g Zn with 73 g HCl, we obtain 2 g H. If twice as
much Zn (130 g) were used, 4 g H could be obtained, with, of course,
twice as much HCl. With 260 g. Zn, how much H could be liberated?
A proportion may be made as follows:--

Zn given : Zn required :: H given : H required.
65       : 260         :: 2       : x.

[footnote: Given, as here used, means the weight called for by the
equation; required means that called for by the question.]

Solving, we have 8 g H.

How much H is obtainable by using 5 g Zn, as in the experiment?

To avoid error in solving similar problems, the best plan is as
follows:--

Zn + 2HCl = ZnCl2 + 2 H	 |      65:5::2:x
65	              2  |      65 x = 10
5	              x	 |      x = 10/65 = 2/13	Ans. 2/13 g.

The equation should first be written; next, the atomic or molecular
weights which you wish to use, and only those, to avoid confusion;
then, on the third line, the quantity of the substance to be used, with
underneath the substance wanted. The example above will best
how this. This plan will prevent the possibility of error. The proportion
will then be:--

a given : a required :: b given : b required.

How much Zn is required to produce 30 g. H?

Zn + 2HCl = ZnCl2 + 2H    |    2:30::65:x
65                   2    |     2x = 1950
 x                  30    |      x = 975    Ans. 975 g. Zn.

Solve:--

(1) How much Zn is necessary for 14 g. H?

(2) How many pounds of Zn are necessary for 3 pounds of H?

(3) How many grams of H from 17 g. of Zn?

(4) How many tons of H from 1/2 ton of Zn?

Suppose we wish to find how much chlorhydric acid--pure gas--
will give 12 g. H. The question involves only HCl and H. Arrange
as follows:--

Zn + 2HCl = ZnCl2 + 2 H	  |  H giv. : H req. :: HCl giv. : HCl req.
       73             2   |    2    :   12   ::  73          x
        x            12   |       2x=876                x=438
                                                    Ans. 438 g. HCl.

Solve:--

(1) How much HCl is needed to produce 100 g. H?

(2) How much H in 10 g. HCl?

(3) How much ZnCl2 is formed by using 50 g. HCl? The question
is now between HCl and ZnCl2.

Zn + 2HC1 = ZnCl2 + 2H
       73     136       |  Arrange the proportion, and solve.
       50       x

Suppose we have generated H by using H2S04: the equation is
Zn + H2S04 = ZnSO4 + 2 H. There is the same relation as before
between the quantities of Zn and of H, but the H2S04 and ZnS04 are
different.

How much H2SO4 is needed to generate 12 g. H?

Zn + H2SO4 = ZnS04 + 2 H
        98             2     |   Make the proportion, and solve
         x            12

Solve:--

(1) How much H in 200 g. H2S04?

(2) How much ZnS04 is produced from 200 g. H2S04?
(3) How much H2S04 is needed for 7 1/2 g H?
(4) How much Zn will 40 g. H2SO4 combine with?
(5) How much Fe will 40 g. H2SO4 combine with?
(6) How much H can be obtained by using 75 g Fe?

These principles apply to all reactions. Suppose, for example, we
wish to get l0 g. of O: how much KClO3 will it be necessary to use?
The reaction is:--

KClO3 = KCl + O3   |     48 : 10 :: 122.5 : x
122.5 	      48   |
x	      10   |     Ans. 25.5+ g. KClO3.

The pupil should be required to make up problems of his own,
using various reactions, and to solve them.

CHAPTER X.

CARBON.

Examine graphite, anthracite coal, bituminous coal, cannel coal,
wood, gas carbon, coke.

40. Preparation of C.

Experiment 26.--Hold a porcelain dish or a plate in the flame of
a candle, or of a Bunsen burner with the openings at the bottom
closed. After a minute examine the deposit. It is carbon, i.e.
lamp- black or soot, which is a constituent of gas, or of the
candle. Open the valve at the base of the Bunsen burner, and hold
the deposit in the flame. Does the C gradually disappear? If so,
it has been burned to CO2. C + 2 O = CO2. Is C a combustible
element?

Experiment 27.--Ignite a splinter, and observe the combustion and
the smoke, if any. Try to collect some C in the same way as
before.

With plenty of O and high enough temperature, all the C is burned
to CO2, whether in gas, candle, or wood. CO2 is an invisible gas.
The porcelain, when held in the flame, cools the C below the
point at which it burns, called the kindling-point, and hence it
is deposited. The greater part of smoke is unburned carbon.

Experiment 28.--Hold an inverted dry t.t. or receiver over the
flame of a burning candle, and look for any moisture (H2O). What
two elements are shown by these experiments to exist in the
candle? The same two are found in wood and in gas. Experiment
29.--Put into a small Hessian crucible (Fig. 18) some pieces of
wood 2 or 3 cm long, cover with sand, and heat the crucible
strongly. When smoking stops, cool the crucible, remove the
contents, and examine the charcoal. The gases have been driven
off from the wood, and the greater part of what is left is C.

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