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warm gently. Also note odor of ammonia.

The metals lower than zinc in the electro-motive series give no H
with nitric acid, and those below hydrogen do not give H with any



LABORATORY MANUAL OF GENERAL CHEMISTRY 31

acid. Try the action of con, nitric acid diluted with an equal volume
of water, on a little tin, copper, powdered antimony. Oxides are ob-
tained with the first and third metals. Would HC1 act on the copper
and antimony? Could HNO 3 and metals be used to prepare pure H?

53. Nitric Oxide: Use apparatus as in fig. 3. Put in flask 25
grams granulated copper, about 10 cc. water, see that thistle tube
reaches into the water, then add con. nitric acid as necessary to secure
a moderate flow of gas. Reject the first half jar full of gas. Fill three
jars, leaving one on the shelf of the trough. Pass some of the gas
through a solution of ferrous sulfate in a tube. The dark color is due
to FeSOiNO. What does the blue solution in the flask contain? Pour
it into a vessel provided for the purpose. Wash the ^remaining copper
and put into the vessel provided for it.

Prepare oxygen as in 6 or 9 and pass a little into jar on shelf.
The red gas is nitrogen dioxide, NO 2 . Let it become absorbed then pass
in more oxygen. Thus continue till the water ceases to rise in the
jar. Write the volume equation for the union of NO and 2 . What is
formed when NO 2 dissolves in oold water; in hot water?

In one jar of NO burn red phosphorus. Try a candle in the other.

Express the action of nitric acid on copper in two equations, the
first of which shows the decomposition of the acid in oxidation as in
equation (2), 51, forming 3CuO; the second the dissolving of this oxide
in the acid.

54. Reduction of a Nitrate to Nitrite, Nitrous Acid: (a) In an
iron crucible heat and stir with an iron rod, spike nail, 5 grams of
potassium nitrate and 20 grams granulated lead till the mass glows.
When cold add water and boil for some time. Filter off the liquid into
a tube. Add an excess of dil. H 2 SO 4 . Test the gas with moist starch
iodide paper. The sulfuric acid sets free nitrous acid which breaks
up into water, NO and NO-; equations. Note that NO+NO 2 =N 2 O 3 , the
anhydride of nitrous acid. It exists only as a liquid.

(b) Read (a) carefully. In a flask with thistle tube and right-an-
gled delivery tube place 10 -grams sodium nitrite, add enough water to
cover end of thistle tube, place delivery tube in 5 cc. NaOH in a wide
test tube. Add about 25 c.c. dil. sulfuric acid to the flask. Nitrous acid is
set free, but breaks up as in (a) . The gases are absorbed by the NaOH
making NaNO 2 . Add dilute acid to this solution and test the gas as
in (a).

55, Nitrogen Dioxide, Nitrogen Tetroxide: The lead nitrate used in
this experiment should be prepared in quantity before the laboratory
period by crushing to moderate fineness in a mortar and heating for
three hours in an oven at about 125.

Heat 10 grams of the dried lead nitrate in iron tube shown in fig.
13, turning the delivery tube down, and placing it in a small dry flask.



32 LABORATORY MANUAL OF GENERAL CHEMISTRY

Heat until the flask is filled with the red-brown gas, NO 2 mixed with
N 2 Oi. Stopper the flask and heat it high over a flame, but do not heat
so much as to burst the flask. A temperature of 142 is sufficient to
change all the gas to NO 2 . Note depth of color. Let the flask cool a
few moments in air, then under running water, and observe the depth
of color again, when 80% of the gas will consist of colorless N 2 0u
Write the equation for the production of the gas and the reversible
reaction of the change from one to the other constituent of the mixture.

Heating lead nitrate again pass the gas into about 3 cc. of sodium
hydroxide for a few moments, then add dilute sulfuric acid to the
solution. What evidence have you that a nitrite was formed by the
action of the gas on sodium hydroxide? What else was formed? See
text book for the action of this gas with cold water and with hot water.

56. Tests for Nitrogen and the Nitrate Radical: (a) Tests for ni-
trogen in organic matter: Heat in a test tube with soda-lime or a mix-
ture of lime and powdered sodium hydroxide, bits of woolen material,
such as yarn, or bits of leather, dry albumin or corn meal, and hold in
the mouth of the tube wet turmeric paper. Is ammonia given off?

Secure an imperfect test tube and heat in it any of the organic
substances mentioned, with a bit of sodium not larger than half a pea.
(Do not touch sodium with the wet hands). Heat strongly till the
reaction is complete, and standing well back place the hot end of tube
in a little water in a beaker. The end cracks off. Boil the water and
filter. To a portion of the filtrate add a little solid ferrous sulfate,
then a few drops of ferric chloride, and boil. Now make acid wiih
dilute HC1, when a deep blue color will result. To'the rest of the solu-
tion add a crystal of potassium nitro-ferri-cyanide, which will give a
red color, showing sulfur in the organic matter.

(b) Tests for the nitrate radical, or nitric acid: To a few cc. of a
solution of ferrous sulfate add a very little of any nitrate, and when
the substance is dissolved and the solution is cool incline the tube and
pour in steadily con. H 2 SO 4 , so that it will run down and collect at the
bottom of the tube. Where it and the solution meet will form a dark
ring of FeSO. (NO).

The following test should be used only for excessively small
amounts of nitrate: Upon a bulk of any nitrate not larger that a pin
head and in a dish, drop about ten drops of phenol-disulphonic acid.
Warm the dish gently, best on a water bath for a few moments. Add
about 25 cc. of water and make alkaline with ammonia. A yellow
solution shows nitrate radical is present.

ELECTRO-CHEMISTRYTHEORY OF IONIZATION.

57. Electrical Terms and Fundamental Laws: Using good text
books on chemistry and on physics study, till clear to you, the meaning



LABORATORY MANUAL OF GENERAL CHEMISTRY



33



of these terms: anode, cathode, Volt, Ampere, Ohm, Coulomb, Watt,
electro-chemical equivalent, electro-motive series of the elements.

What is Ohm's Law? On a 110-Volt circuit find the current
strength or amperage transmitted by a 25-Watt lamp. Find the resis-
ance of this lamp in Ohms.

What is Faraday's Law? What are the electro-chemical equiva-
lents of H, O, Cl, SO 4 , NO 3 , Cu, Ag, Sn". Sn""? Give relations of
electro-chemical equivalents, atomic weights (or in the case of radicals
the sum of the atomic weights), and valences.

>*. Electrical Coiuluctiyity : The current used is the direct light-
ing circuit, 110 volts, cut down by a 25-Watt lamp. This would give
what amperage through a wire without resistance connecting th,e two
binding posts? Calculate and read the ammeter. Do the results agree?
Determine the comparative conductivity of the following 5th normal
solutions, already made by the instructor: hydrochloric acid, sulfuric
acid, acetic acid, sodium acetate, sodium hydroxide and ammonium hy-
dioxicle. Since they are all N/5 they have the same number of chemical
equivalents per unit volume. According to whose law might they be
expected to conduct the same?

To determine the conductivity secure one of the conductivity tubes

as shown in fig. 14, wash, rinse
with distilled water and drain it.
In each case be careful thus to
clean the tube. Paste a strip
of gummed paper on it and
in each case fill to this
mark. Connect the tube thus
filled with the binding posts,
note the intensity of the glow of
the lamp and read the ammeter.
Thus determine the conductivity
of all. Why should they conduct
so differently? Knowing the re-
sistance of the lamp and the cur-
rent it alone transmits, calculate
from one of your readings of the
ammeter the resistance of the
Fig. 14. solution?

Fill the conductivity tube with a neutral solution of sodium or pot-
assium sulfate, add a few drops of litmus solution and mix well, and
subject the solution to the action of the current. Which electrode
gives off oxygen and shows the formation of acid around it; which
shows hydrogen evolved and alkali formed around it? Try a solution
of common salt without litmus solution. Prove with starch-iodide pa-




34 LABORATORY MANUAL OF GENERAL CHEMISTRY

per that Cl is given off at the anode. Test the solution at the cathode
with turmeric paper. By what secondary reaction is alkali formed in
the last two instances? What is the action of sodium on water? (13)

In electrolysis many of the heavy metals instead of acting upon
water at the cathode are there deposited. Subject a solution of cop-
per sulfate to electrolysis for several minutes. What is deposited on
the cathode? t What gas is given off at the anode? Copper sulfate
itself reacts slightly acid, but if the solution at the anode be tested it
will be found much more acid. How do hydrogen and the metals ac-
cumulate at the cathode and the acid radicals, with which they were
associated, at the anode?

59. Chemical Facts Best Explained on the Theory of lonization:
The Mature of Acids: Test with blue litmus paper dilute HC1, dilute
HNO 3 , dilute H 2 S0 4 , acetic acid and any other acids that may be avail-
able. Why should substances of such different composition all turn
the paper red? Why should they all taste sour? Try the action of
each on bits of zinc. Why should all give hydrogen? Why should
they all neutralize bases giving salts and water? Why should they all
give hydrogen at the cathode when electrolyzed?

It would seem that H is the one component of all acids, and that
to it their acid properties are due. In electrolysis H accumulates at
the cathode and the rest of the acid molecule at the anode. It is not
far to the thought that the H is, in the solution of an acid, compara-
tively free from the rest of the molecule. Since unlike electric
charges attract each other and like charges repel, the inference is that
the H atom is charged positively thus, H + , and the remainder of the
molecule, for example, Cl is charged negatively, thus, Cl". In this con-
dition the H and Cl atoms are called ions. Ions are formed when acids,
bases and salts are dissolved in water and without regard to any in-
fluence of the electric current.

60. The Character of Bases: Test with turmeric paper solutions
of sodium hydroxide, potassium hydroxide, ammonium hydroxide, cal-
cium hydroxide, barium hydroxide. Again, why should such different
substances all turn the paper brown? They also all neutralize acids in
the same way forming salts and water. Their common constituent is
hydroxyl OH. Since all bases have OH it is inferred that the alka-
linity is due to this group. It seems to be easily separable from the
metal of such group as NH 4 . In electrolysis it travels to the anode
where it breaks up into water and oxygen while the metal goes to the
cathode. For reasons given under acids, it is believed that a base in
solution is more or less ionized. That is, sodium hydroxide consists
largely of the ions Na + and OH".

61. Ready Cleavage or lonization of Salts: In as many test tubes
place a few drops of solutions of the following: NaCl, KC1, NH 4 C1, CaCla



LABORATORY MANUAL OF GENERAL CHEMISTRY 35

BaCl 2 and other chlorides that may be at hand. Add to each a few
drops of silver nitrate. Why should all these different chlorides gives
the same precipitate of silver chloride? Silver sulfate or silver ace-
tate might have been used instead of silver nitrate and precisely the
same precipitate of silver chloride would have resulted. In the solu-
tions of chlorides it is evident that chlorine is very slightly held by the
metals if at all, and the same is true of the silver in the solutions of the
silver salts. All these salts are electrolytes, the metals going to the ca-
thode and the non-metals to the anode. The inference is that they are
largely ionized in solution. Thus, sodium chloride is largely Na + and
d~, and silver nitrate is Ag + and NO 3 ~.

Any element as Cl is not always an ion in solution. To solutions of
pure potassium chlorate, chloral and chloracetic acid add a little silver
nitrate solution. No silver chloride is obtained, since KC1O 3 ionizes into
K + and C10 3 ", chloracetic acid into H + and CH 2 C1CO 2 ~, while chloral
hydrate gives no ions.

62. Degree of lonization: Refer to your experiment on conduc-
tivity (58). Did all the acids conduct equally well and were they
equally ionized? Compare the conductivity and ionization of sodium
hydroxide and ammonium hydroxide ; of acetic acid and sodyAm acetate.

The ionization of the same substance may be increased by diluting
and decreased by concentrating its solution.

(a) Compare the colors of 2-normal solutions of copper sulfate,
nitrate and chloride. The color of each is supposed to be due to the
color of the undisscciated salt and to the copper ion. Now dilute a
small portion of each solution with 10 times its volume of water. Why
are the solutions now more nearly the same color? To a portion of
each solution add an excess of ammonia. The same color is due to the
same ion, Cu(NH 3 ) 4 ++ ,

(b) The concentration of a solution may be in effect increased
and the dissociation of the solute decreased by adding a substance hav-
ing an ion in common with the solute. Solid copper bromide is black,
its concentrated solution is brown due to CuBr 2 , while its dilute solu-
tion as that of every other cupric salt shows blue due to the Cu ion. In
a dish dilute about 2 c.c. of the brown solution till it becomes blue. To
one half of the blue solution add a few drops of con. HBr, which has
the common ion Br, till brown. To the other half add solid copper
chloride, having the common ion Cu, till brown. Explain how the ad-
dition of the common ion effects these changes.

(c) Dilute a little acetic acid from shelf bottle with 20 times its
volume of water. Add a few drops of methyl orange and divide into
two portions. To one add one half its volume of con. sodium acetate
and compare its color with that of the other half. What common ion
was added and what was the effect on the acidity of the acid?



36 LABORATORY MANUAL OF GENERAL CHEMISTRY

(d) To a saturated solution of salt add concentrated HC1 till a
large precipitate of salt is obtained, and account for its formation.

63. Acidity Due to Hydrolysis: Many substances containing no
hydrogen give an acid solution. They are mostly salts of metals which
form weak bases and radicals of stronger acids. With blue litmus pa-
per test solutions of salts of copper, iron, aluminium. In these cases
the hydrolysis goes only a little way, for example thus:

FeCl 3 +H 2 0=(reversibly)FeCl,OH+HCl.

Add a little antimony chloride and bismuth chloride to five times
their volumes of water. Here the reactions go far to the right precipi-
tating SbOCl and BiOCl. Now reverse the reactions by adding con.
HC1. See the hydrolysis of the halides of phosphorous, 34 and 79.

64. Alkalinity Due to Hydrolysis: Some salts of strongly basic
metals and weak acids give alkaline solutions due to hydrolysis. Test
with turmeric paper or a few drops of phenol-phthalein solutions of bor-
ax, sodium carbonate, Na 2 CO3, and sodium phosphate, HNa 2 POi. In the
case of sodium carbonate, Na 2 CO 3 +H 2 O=HNaC0 3 4-NaOH, and of
course the last is highly ionized, and the alkalinity is due to the ion
OH~. For olher examples see 77 and 95.

65. The Electro-Motive Series of Elements: In the following any
metal which replaces another from solution is said to have a greater
solution tension or to be more electro-positive. In a little zinc sulfare
solution place bits of magnesium turnings and let stand. When the
action has nearly ceased note gray deposit of zinc. Place zinc in a so-
lution of cadmium chloride and later note cadmium deposited on the
remaining zinc. Try cadmium or zinc in solutions of copper sulfate
and lead acetate and note copper and lead deposited. Try iron in a
copper solution. Place a strip of copper in a solution of mercuric
chloride and after a few minutes remove, rub and note mercury coat-
ing. Put a copper wire in a silver solution and note deposit of silver,
Try silver in a solution of gold chloride and note deposit of gold on
the silver. All these cases are practically alike. One metal goes into
solution as ions and the other is as it were forced out as neutral metal;
for example, Cu ++ +SO4- + Zn=(reversibly)Zn ++ +SO 4 "+Cu. Write a
similar ionic equation for the preparation of H with zinc and sulfuric
acid. Has the SO 4 much to do with either case?

Arrange the above metals in the order of their capacities to replace
other metals, or their ionizing tendency. Compare the result with the
arrangement of the Electro-Motive Series in a text-book. Wh'at two
metals above if used for the plates in an electric battery cell would
give the greatest electromotive force?



LABORATORY MANUAL OF GENERAL CHEMISTRY 37

SULFUK.

<;#. Solubility and Crystallization: Do not heat carbon disulfide
or have a flame near it, since it is very volatile and easily inflam-
mable.

Place in a dry test tube about 2 grams of powdered sulfur, add
not more than one-fourth test tube full of carbon disulfide, shake and
filter through a dry filter into a crystallizing dish or small beaker.
Let two or three drops fall into a clean watch glass. After the liquid^
has evaporated at room temperature, examine the crystals in each ves-
sel, and those in the watch glass with a microscope. The crystals be-
long to the rhombic variety of sulfur.

<J7. Effects of Heat, Allotropic Forms: Since the test tube can-
not be cleaned fill an imperfect one three-fourths full of lumps of
sulfur, slowly and evenly heat till it is all changed to a yellow, mobile
liquid. Now increase the temperature and note that it becomes darker.
Find a temperature at which the tube may be inverted for a moment
without the sulfur's running out Increase the temperature till it
shows signs of boiling and becomes quite fluid again. Pour in a steady
small stream into a beaker or other 'vessel full of water. Examine
this "plastic sulfur", place aside and examine at the end of the lab-
oratory period and at the next period. It gradually changes to mono-
clinic sulfur, and after a long time to rhombic, the permanent form.
Consult text-book on the forms of sulfur, and their properties.

<js. Hydrogen Sulfide: Fit a small bottle or flask, the former pre-
ferred, with a delivery tube consisting of two right angled pieces joined
with rubber tubing, the outer piece long enough to reach to the bot-
tom of the collecting vessel or test tube when resting, on the desk.
Place in the generating vessel 20 grams of ferrous sulfide in small
bits, sliding in the larger pieces to avoid breakage if a flask is used,
add about 40 c.c. of water and drop directly upon it a little at a time
con. sulfuric till a suitable flow of gas is secured. If the flow of gas
becomes too slow at any time do not add more acid, but pour off the
liquid which is nearly exhausted of acid but contains much iron salt,
and add water and acid as in the beginning.

Collect a bottle of the gas by displacement of air, in the same
way as chlorine, and burn the gas in the bottle. What is the deposit
on the sides of the bottle? Collect gas in a test-tube one- fourth full
of water, cover mouth of tube with the thumb and shake. Is the gas
soluble in water? Turn upward the outer section of the delivery tube
and light the gas at the orifice. Hold cold porcelain #s a dish or cru-
cible lid in the flame at about its middle. What is the yellow deposit?
Insert the flame into a bottle with wide mouth as far as you can with-



38 LABORATORY MANUAL OF GENERAL CHEMISTRY

out extinguishing the flame. Why does sulfur deposit on the dish and
bottle instead of burning?

69. Precipitation with Hydrogen Sulfide: Hydrogen sulfide is
much used in separating the metals into groups in analytical chemis-
try. In test tubes in the test tube holder place about 5 c.c. of solu-
tions of salts of the following metals, using chlorides, nitrates, ace-
tates as may be convenient: silver, lead, mercury, bismuth, copper,
cadmium, antimony, arsenic, tin; also, zinc, cobalt, nickel, manganese,
iron; also, barium, calcium, strontium, sodium, add a drop or two of
dilute HC1 or HNOs to each. Pass the gas flowing with moderate ra-
pidity into each of these solutions for about a minute, washing off the
delivery tube by dipping into water before inserting it into a new so-
lution. Note carefully what metals can be precipitated as sulfides
with H 2 S from slightly acid solutions remembering the acid added and
the fact that when precipitation occurs acid is necessarily set free.
The precipitation of zinc is not complete. Pass an excess of gas into
the tube containing zinc, filter off the precipitate and add to the fil-
trate and to each succeeding solution, beginning with cobalt, ammon-
ium hydroxide, which should give precipitates of sulfides in all until
barium is reached. That is, several metals not precipitated as sul-
fides in acid solution are precipitated with hydrogen sulfide and an
alkali and they form another group. Name the metals not precipi-
tated as sulfides.

Return to the sulfides precipitated from acid solution, pour off the
liquid from the sulfides of Hg, Cu,- Bi and try to dissolve each by boil-
ing 'with dilute nitric acid. How may Hg be separated from the other
two? Pour off the liquid from the sulfides of lead, antimony and ar-
senic and heat each with about 5 c.c. of ammonium sulfide, but do not
boil. How may lead sulfide be separated from arsenic and antimony
sulfides?

These are merely illustrations of the use of hydrogen sulfide and
many others will be met. Instead of using hydrogen sulfide and am-
monium hydroxide separately to precipitate certain sulfides, it is com-
mon practice to use ammonium sulfide which may be easily made by
saturating diluted ammonium hydroxide solution with hydrogen sul-
fide, and then adding an equal volume of the same ammonia solution
which gives essentially (NH 4 ) 2 S.

70. Reducing Action of Hydrogen Snlfide. Hydrogen sulfide is
not a very stable compound and it acts as a reducing agent in much
the same way as hydriodic acid. Pass hydrogen sulfide into a dilute
acidified solution of potassium dichromate, till green ; into a dilute acid-
ified solution of potassium permanganate till colorless; into bromine
water and a dilute solution of iodine till colorless. In the last two
cases filter off the sulfur and test liquids with litmus paper. What



LABORATORY MANUAL, OF GENERAL CHEMISTRY



39



acids were formed? Compare the reducing action of hydrogen sulfide
with that of sulfur dioxide in experiment 71.

71. Sulfur Dioxide: (Read reference book on sulfur dioxide, sul-
fur trioxide and sulfuric acid.) In a test tube treat a little sodium
sulfite with dilute acid. Note odor and test with a strip of paper mois-
tened with mercurous nitrate. It should turn dark.

Determine whether bits of charcoal and sulfur will give SO 2 when
heated with con. sulfuric acid. Explain their action on the acid. Ar-
range apparatus as in the preparation of hydrochloric acid. Place in
the flask 20 grams of granulated copper or bits of sheet copper or
turnings and add 25 c.c. con. sulfuric acid. Before heating read
through the experiment and have everything needed at hand so as to
continue the flow of gas the minimum of time.

Heat till gas comes off freely and control the rate by turning
down the flame. After acidifying them with acetic acid pass gas into
a solution of potassium dichromate till green and into a solution of
potassium permanganate till colorless; also, into bromine water till
colorless, into dilute nitric acid, and into distilled water. To each so-
lution add barium nitrate and then dilute HC1. The formation of a
white precipitate by barium nitrate, insoluble in HC1 shows the pres-
ence of the sulfate radical, SO 4 .

The first action of SO 2 on passing it into the above solutions was
probably the formation of the unstable sulfurous acid, H 2 SO 3 . All the
substances into which the gas was passed were oxidizing agents except
of course the distilled water. Show their action on the sulfurous acid.
Test for the sulfate radical in the dilute sulfuric acid on the shelf, in
solutions of magnesium sulfate, copper sulfate and other sulfates that
may be at hand.

72. Preparation of Sulfuric Acid: Set up the apparatus as shown
in fig. 15. The ignition tube may be of hard glass or of half inch gas
pipe. If the latter is used it should be 12 to 14 inches long to prevent
the overheating of the stoppers. Even then it is well to spray the ends


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Online LibraryWalter Scott HendrixonA laboratory manual of general chemistry → online text (page 4 of 8)