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A Laboratory Manual
of General Chemistry



A LABORATORY MANUAL



OF



GENERAL CHEMISTRY



BY



W. S. HENDRIXSON,

Professor of Chemistry in Grinnell College.



GRINNELL, IOWA,

1918



ALL RIGHTS RESERVED



PREFACE.

This the fourth edition of the author's Experiments in General
Chemistry is printed, as its predecessors have been, primarily for the
use of students in general chemistry in Grinnell College. This fact
may explain certain departures from custom in the preparation of
such books, such as suggestions to teachers and detailed descriptions
of apparatus and its manipulation. As a matter of fact apparatus at all
complicated is not only shown by cuts, but it is set up on the lecture
table and many experiments for any period are there carried through
before the students enter the laboratory. Some apparatus is even set
up in the laboratory and left there for inspection during the laboratory
perio'd.

Not satisfied to use the same set of even his own experiments year
after year and wishing to provide new laboratory work for classes of
students who have taken chemistry in the high school, the writer has
provided for more laboratory work than can be done in a three- or
four : hour course of one year.

In this book an attempt is made to connect rationally general
chemistry and qualitative analysis. Students who complete a first
year course in chemistry should have some knowledge of qualitative
analysis, but it should not be permitted to take the place of general
chemistry in the second half year, which is usually devoted to study of
the metals. Qualitative analysis ought to be a development from the
general chemistry to which it gives point, and its introduction as an
outgrowth of the general chemistry greatly stimulates the student's
interest in both subjects. In this book tests for acids and other com-
pounds are given in the study of the non-metals, and a system for the
detection of acids is given after the study of the non-metals has been
completed. In the study of the metals emphasis is placed on properties
that are of analytical significance, though other facts are not neg-
lected. After each group of metals has been studied their separation
is taken up, and the work is extended as rapidly as the student's ex-
perience justifies it, to the detection of both metals and acid radicals
in "unknowns." The scheme of qualitative analysis as outlined is not
supposed to be complete but is meant to serve as an introduction to
the subject and a preparation to the more rigorous course in quali-
tative analysis the following year.



387354






TO THE STUDENT.

I. On coming to the laboratory the first day find the number of
your desk, get the key or combination and a printed list of the appa-
ratus the desk should contain. Verify the apparatus, asking the names
of the things you do not know. Make sure that apparatus is wanting
before calling for it. Present broken or faulty apparatus for exchange.

II. After using apparatus, clean it and return it to the desk.
Clean the top of the desk and lock it before leaving. Have old cloths
for cleaning and a towel for the hands. In grading notes you will be
held responsible for the condition of the desk without and within anfl
for the bottles on its shelves, which should always be kept in the
same order.

III. Provide an approved note book of the sort shown in the lec-
ture room. Leave the first leaf blank and enough margins to permit
corrections by the instructor.

Begin every experiment on a new page. Write notes in the labor-
atory in full and do not copy them. Only original notes made while
doing the laboratory work are of value. The notes on each experiment
should have a suitable heading and should have the same number as
the experiment. Paragraph to suit the subject matter. Present the
note book for grading and criticism before leaving the laboratory.

IV. Ascertain in advance what the laboratory work is to be for
each period and prepare for it before coming to the laboratory by use
of the text or reference book. The subject will be announced in the
class room, and references to books will be given. Bring the text-
book to the laboratory.

V. Every experiment is intended to teach something of value.
Try to find out what it is by yourself, using observation and the text-
book, then ask the instructor. State results in the notes. Do not con-
fine these efforts merely to answering the questions of the laboratory
book. For example after equations have been studied in class all
equations for reactions in the laboratory work should be written
whether asked for or not. Write them where they belong scattered
through the notes and do not write them in mass at the end of the
notes.

VI. When using chemicals replace the covers or stoppers of the
containing vessels. Do not throw stoppers upon the desk. Return all
bottles to their places on the shelves. Replace all weights in the
boxes.

VII. Do not wash pieces of apparatus with distilled water but.
with hydrant water. If they are well drained it will not be necessary
in most cases even to rinse them with distilled water. On the other



LABORATORY MANUAL OP GENERAL CHEMISTRY 3

hand always have distilled water in your wash bottle and use it in
making all solutions.

VIII. Throw no solid matter into the sinks but into the jars pro-
vided for that purpose. On the other hand wash apparatus at the
sinks and do not throw large amounts of water into the jars.

DIRECTIONS FOE LABORATORY WORK.
GENERAL MANIPULATION.

1. The Bunsen Burner: Take apart the burner and study its con-
struction. Determine how to regulate the supplies of gas and air. Put
it together and turn on the gas at the cock and regulate the supply by
the screw on the burner. Regulate the gas and air so as to secure a
non-luminous flame. Too much air may cause the flame to blow out,
"snap back" or burn with much noise. A long green hissing flame in-
dicates that the gas is burning also at the base. Turn out the flame,
reduce the amount of air, light again. A flame about 3 inches long is
usually sufficient.

The ordinary flame is used to heat test tubes directly, or to heat
such as flasks and beakers placed upon wire gauze, of which nichrome
gauze is best. The crown top is used to heat beakers and flasks with-
out protection of gauze.

The Wing Top : Put the wing top on the burner, turn on the gas
and regulate gas and air so as to secure a just non-luminous flame
about as high as broad. Too much air is objectionable. Such a flame
should be used exclusively for bending tubing.

'2. Breaking and Bending Glass Tubing: Draw once a sharp, three-
cornered file across the piece of tubing where you wish to break it.
Hold the tube with both hands, with thumbs together and opposite the
scratch. A slight pull will break the tube squarely at the scratch.

To bend glass tubing always use the wing top. No one but an ex-
pert can make a gcod bend with the flame of the ordinary burner. A
bend so made will be uneven, crinkled and the tube is likely to break
at that point.

Hold the tube above the middle of the wing flame, having its
length in direction of the breadth of the flame. Revolve the tube and
move it back and forth in the direction of its length until it softens
and begins to yield to a slight pressure, then bend it slowly as de-
sired. If it shows a tendency to collapse or flatten at any point, stop
bending at that point, heat at one side or the other and there complete
the bend. The tendency to collapse shows that the bend is being made
too short. Practice with scraps of tubing until you can make a good
bend, and then make the tubes like the samples shown in fig. 1.
They represent the tubes most used in this course, and should be kept



LABORATORY MANUAL OF GENERAL CHEMISTRY




Fig. 1

throughout the year and not cut up to make other things. Heat the
ends of the tubes to redness in the ordinary flame to fuse down the
sharp edges. Other glass working will be shown in the class room as
occasions arise.

If there is no wash bottle in the desk construct one as shown in
fig. 1. This wash bottle should always contain a supply of distilled
water and should not be torn down to use the tubes or flask for any
other purpose.

3. Weighing. The following may be applied to all balances and
weighings, but will be supplemented by the instructors when weigh-
ings of great accuracy are required.

Never place chemicals, other than pieces of metals, directly upon
the pans of the balance, but in some suitable containing vessel. When
only moderate accuracy is required, balanced papers may be used, but
not where accurate weighings are called for. In the latter case two
methods are good. Place a dish on the left hand pan and weigh it ac-
curately. Place in it about the desired amount of substance and weigh
again. Of course the difference between the weights gives the weight
of the substance. The scales rarely "balance" or the pointer rarely
stands at the zero point. This error, however, is eliminated by the
above method. Instead of the dish, the substance may be weighed in
a corked tube, then the desired amount may be taken out and the tube
weighed again. Of course in both weighings the tube must be in the
same pan, always the left.

When equilibrium has been attained, that is, when the pointer
makes excursions equidistant right and left from the center, count the
weights without removing them from the pan, record the weight in the



LABORATORY MANUAL OF GENERAL CHEMISTRY 5

note bcok and verify by counting the weights again as they are re-
moved to the box. Write the weight in the book as one number. If
the weights are 5 g., 2 g., 200 mg., 50 mg., write the total at once 7.25
grains. Unless the nature of the experiment requires it, it is a mis-
take to try to weigh a definite amount of a substance. For example, if
the directions say "Weigh accurately about 5 grams of the substance,"
do not try to get just five grams, but take about five grams and weigh
it accurately.

4. Pleasuring Volumes of Liquids: Study a pipet and a gradu-
ated cylinder. Why is the cylinder graduated from the top downward
and from the bottom upward?

Weigh accurately a small flask on the horn-pan scales observing
the directions given under weighing. Now put a small piece of rub-
ber tubing on the larger end of the pipet, by suction fill it with dis-
tilled water to above the mark and pinch the rubber tube. Carefully
let out the water to the mark and then run the remainder into the
flask and weigh again. Find the weight of the water, the weight of
1 cc. and the error in the pipet according to your work. Why in this
experiment does it make little difference whether the balance with
pans empty was in exact equilibrium or not?

OXYGEX.

5. Preparation of Oxygen: (Study text-book in advance). Many
substances containing it give off all or a part of their oxygen when
heated. The following are illustrations:

In a small test tube heat about half a gram, estimated, of potas-
sium chlorate. It melts and then seems to boil owing to the evolution
of oxygen. Light a splinter or tooth pick, blow out flame, lower glow-
ing end into the test tube. It should rekindle.

In another small tube, preferably one made of "hard glass" tubing
heat a little mercury oxide persistently and test with glowing splinter.
Note sublimed mercury on wall of tube. By persistent heating all the
mercury oxide may be decomposed into mercury and oxygen.

As in the case of mercury oxide heat a little manganese dioxide
and test for oxygen. Only one-third of the oxygen is given off.

Oxygen may be obtained also by heating lead dioxide, potassium
permanganate, potassium perchlorate, barium dioxide to redness.

All these instances illustrate chemical change, and the nature of
the change is that of decomposition.

({. Preparation of Oxygen, Laboratory Method: (a) Read through
the experiment and have everything required within reach. Set up
the apparatus as shown in fig. 2, having trough filled with water to
about 2 inches above the shelf. Place the delivery tube well to the
farther side of the trough so as not to be obliged to reach over it.



LABORATORY MANUAL OF GENERAL CHEMISTRY




Fig. 2.

Fill two jars* with water by immersing in the trough with mouth
slightly upward, inverting them and placing upon the shelf as shown.
Direct the base of the retort stand backward so that it will not be in
the way of the burner. (See fig. 2). There it no need of clamping the
test tube tightly so as to endanger breaking it. Have the clamp near
its mouth. Why?

Weigh approximately on platform scales 8 grams potassium chlor-
ate and 4 grams powdered manganese dioxide, mix them on paper with
a spatula and from the paper slide the mixture into the test-tube.

Now heat the substance in the tube slowly and evenly, best by
holding the burner in the hand and moving it back and forth along the
tube, so as to avoid over-heating and softening the tube at any one
point. So regulate the heat that the gas shall be coming off slowly
when the jar is about full. When the jar is full slide it to one side
and place another jar over the mouth of the tube, then place the cover
securely on the full jar keeping its mouth under water, remove it *o
the desk and clamp on the cover. Fill five jars or bottles. When the
gas ceases to come off remove the stopper of the tube to prevent a
back flow of the water. Allow the tube to cool and meantime use the
oxygen in 7. Return then to (b).

(b) Prepare a funnel with filter paper. Fold a filter in halves,
then in fourths, open out one thickness making a cone, press down
evenly into a funnel and wet it with water to make it hold its shape.
Fill half full of distilled water the tube used to heat the potassium
chlorate and manganese dioxide, and when the residue is wet through-
out by shaking heat to boiling and filter by pouring the contents into
the filter, being careful rot to run it over, and catch the clear liquid,
filtrate, in a large test tube or beaker. If not clear run it through
again. To a little of the clear filtrate in a clean test tube add a few

* Rubber seal, pint fruit jar.



LABORATORY MANUAL OF GENERAL CHEMISTRY 7

drops of solution of silver nitrate. Now add a few drops of dilute ni-
tric acid. The white precipitate is silver chloride. The formation of
this white precipitate by silver nitrate in the presence of nitric acid is
a much used test for a chloride. Make solutions of potassium chloride
and potassium chlorate from the shelf bottles, add a little dilute ni-
tric acid to each, then silver nitrate. Which gives silver chloride?
What does your clear filtrate seem to contain? Evaporate a little of
it to dryness in a porcelain dish. Compare the appearance and taste
of residue with potassium chloride and chlorate from shelf. What
chemical change took place on heating potassium chlorate? Was the
manganese dioxide changed chemically on heating? For the use of
manganese dioxide as a "catalyzer" see (8).

7. Properties of Oxygen: Place about half a gram of sulfur in
a deflagration spoon, best covered with a bit of asbestos paper, ignite
the sulfur and lower it into a jar of oxygen. When the combustion
ceases, add a little distilled water to the jar and shake. Test the water
with blue litmus paper. The change to red shows acid formed by the
union of water with sulfur dioxide produced by the combustion.

Ignite a piece of charcoal on a clean spoon and lower into a jar
of oxygen containing a little water. Cover jar, shake and test the
water with blue litmus paper. A faint red should be given the paper
showing the formation of carbonic acid. Add to the jar clear lime
water* and shake. The milky appearance is due to calcium carbon-
ate, produced by calcium hydroxide in the lime water and carbon di-
oxide.

Place a little red phosphorus on asbestos paper in the spoon, light
it and quickly lower into oxygen. Test the water in the jar with blue
litmus paper. Phosphorus pentoxide is 'first formed and this unites
with the water forming phosphoric acid. What is an element? All
three of the substances burned are elements. These are non-metals,
and such on combustion usually form oxides that are -acidic or unite
with water to form acids.

Heat the end of a piece of picture wire, dip into powdered sulfur
for an instant. A portion of the S will adhere and burn. Lower it
into a jar of O. The sulfur burns and then the iron burns with a
shower of sparks.

Without removing the kerosene which adheres to it place a bit
of sodium as large as a grain of wheat in a spoon, ignite the kerosene
and lower into a jar of oxygen. The kerosene should burn and ignite

*If lime water is not present in the laboratory in quantity, it may
easily be prepared by shaking a little slaked lime in a jar of water
for some time, letting the lime settle and filtering. The funnel should
be placed in a flask to protect the filtrate from carbon dioxide in the
air.



LABORATORY MANUAL OF GENERAL CHEMISTRY

the sodium. Shake the bottle and test the water with red litmus pa-
per. The so-called alkali metals such as sodium burn and form oxides
which unite with water forming an alkali.

The burning of these elements forming compounds, oxides, illus-
trates chemical change, and chemical reactions of the type called di-
rect combination or synthesis.

8. Manganese Dioxide as a Catalyzer: In a test tube heat about
1 gram of potassium chlorate till it melts and begins to give off oxy-
gen. Without cooling drop a very little manganese dioxide upon the
fused salt. Is there much change in the rate of giving off oxygen?
Compare temperature required when oxygen is prepared from a mix-
ture of potassium chlorate and manganese dioxide, and from potassium
chlorate alone. The next experiment illustrates further the influence
of catalyzers, and also a very good method of preparing oxygen.

9. Oxygen from Sodium Dioxide (Peroxide) : In each of three dry
test tubes place about a gram of sodium dioxide. In one place also a
very little fine copper oxide and in another powdered manganese di-
oxide. In each of the three pour about 5c.c. of water and note rates at
which oxygen is given off.

To prepare a larger volume of oxygen by this method set up the
apparatus as in fig. 10, but use a dry flask instead of the test tuba.
Place in flask about 10 grams of sodium dioxide, then about half a
gram of powdered copper oxide or manganese dioxide, shake to mix
and spread the mixture evenly over the bottom of the flask. Fill the
funnel with water and by means of the pinch cock let it run in slowly
so as to maintain a suitable flow of oxygen. No heating is necessary.
The oxygen may be tested with a glowing splinter. Sodium hydroxide,
NaOH, is formed at the same time. Test a little of the solution in
the flask with red litmus or turmeric paper. Test sodium hydroxide
from the shelf with the same paper.

HYDROGEX.

11. (a). In as many test tubes place bits of magnesium turnings,
aluminium turnings or wire, zinc, iron filings, or other finely divided
iron such as steel wool; tin, copper, lead. To each tube add dilute
hydrochloric acid. In what cases is hydrogen, a colorless gas, given
off? In cases where it is not, add a few drops of concentrated hydro-
chloric acid. If some metals still resist warm the acid.

(b). In clean tubes and fresh metals try the same series with di-
lute sulfuric acid warming where necessary. In text-book refer to
"electro-motive series." From the more electro-positive end of the
series the metals give off H with decreasing readiness till hydrogen
itself is reached. The metals beyond or below H do not give H with
acids. That is, the metals that are more electro-positive than H dis-



LABORATORY MANUAL OF GENERAL CHEMISTRY




place it from solution. There are secondary reasons why some met-
als above H do not evidently replace hydrogen. Lead is an example,
(c). For the action cf nitric acid on metals see 52.
12. Preparation of Hydrogen. Caution: Mixtures of hydrogen
and oxygen and hydrogen and air are dangerously explosive. In the

preparation of hydrogen in
this experiment and else-
where have no flame near the
delivery tube until all air is
expelled from the flask. . The
gas should be lighted the first
time with a test tube of burn-
ing gas. Should the stopper
of the flask be removed so as
to permit the entrance of air.
Fig. 3. the same precaution must be

used in lighting the gas the second time.

In a small flask fitted as in Fig. 3 place about 25 grams of granu-
lated zinc and about 50c.c. of dilute sulphuric acid. Add a few drops
of a solution of copper sulphate if the action proceeds too slowly when
sulfuric acid is used. To get the crystals mentioned below it is neces-
sary to u~e rrulphuric acid. In performing the experiment subsequent-
ly, inrtead of dilute sulphuric acid the zinc may be covered with water
and then strong hydrochloric acid cautiously added through the fun-
nel tube until the gas comes off freely. Collect the gas in jars reject-
ing the first jar full. Why? Collect two jars and then light the gas
with a test tube of burning gas. That is, hold the delivery tube up-
ward, and place over its end a small test or specimen tube. The hy-
drogen will rise and force the air downward. When the tube has had
time to fill move it mouth downward to a flame, which should be a
foot or two removed, and the H will light with a slight noise if pure.
Carry the tube back and lower it for an instant over the delivery tube.
Hold the flame inside the mouth of a dry bottle and continue until the
liquid deposited collects in drops. Taste it and test it with litmus pa-
per. What is it? In case the evolution of gas becomes too slow it is
due to exhaustion of the acid and the accumulation of zinc sulfate, or
chloride if hydrochloric acid was used. Merely adding more acid
does not suffice.' It is better to pour off the solution and replace it
with fresh acid as in the beginning.

Fill a jar by pouring hydrogen upward into it from another jar
and prove the presence of H in the jar by applying a flame to its
mouth.

Hold a jar of H mouth downward, remove cover and
insert a bit of lighted candle held on the end of a file or wire. Remove



10



LABORATORY MANUAL OF GENERAL CHEMISTRY



candle when it will light again. Repeat several times. Does a candle
burn in hydrogen?

When the evolution of gas in the flask has nearly ceased filter
the liquid into a dish. If sulfuric acid was used crystals of zinc" sul-
fate will appear when it becomes cold, or after it has been evaporated
down one half and cooled again. If hydrochloric acid was used eva-
porate to dryness to obtain zinc chloride. Place some of it on a glass
plate and observe at the next period. Is it hygroscopic?

13. Hydrogen from Water: (a) Sodium should be handled with the
rorceps or dry hands. Press a piece of the metal tightly into a 22 car-
cridge shell. Fill a test tube with water, drop the shell into the trough
d,nd collect the gas by displacement of water. Test the gas for hydro-
gen.

(b) Set up the apparatus as shown in fig. 4 using a half inch gas
pipe at least a foot long. Put near the middle of tube about 10 grams
iron turnings held in place by loose plugs of steel wool. To protect
the stoppers wrap cotton around the ends of the tube and keep it sat-
urated with water. Use a very small flask and only lOc.c. of water in
it. Heat strongly the middle of the iron tube and after several min-
utes boil the water in flask. After the air has been driven out of the
tube collect and test the hydrogen. Prevent a back flow by removing
delivery tube from the trough before removing burner from the flask.




Fig. 4.

The experiment may be continued till a large amount of the iron is
oxidized when it may be used in 14b; or, when cold more of the iron
may be "rusted" by wetting it and putting aside for a day or two. It
may then be heated and dried with a current of air before use in 14b.

In this experiment the reaction is shown from left to right:

3Fe-f4H 2 O=(reversibly)Fe 3 O4+4H 2

while in 14b it goes from right to left, if the contents of this tube or
magnetite is there used as provided for.

14. Hydrogen as a Reducing Agent: The experiment may be per-
formed as in (a) or (b).



LABORATORY MANUAL OF GENERAL CHEMISTRY



II




(a) Place in a piece of hard glass
tubing a column of granulated cop-
per oxide using loose plugs of as-
bestos to hold the oxide in place.
The tube may be drawn out and
bent at right angle as shown in
Fig. 5 or a small right angled tube
may be connected with its outer
end by rubber. Connect with the
flask which contains zinc, and add


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