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Walter Scott Hendrixon.

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acid is set free, but no chlorine. Though H 2 SO4 may be reduced and
HC1 oxidized, they are too stable to act on each other.

Though statements to the contrary are common, hydrobromic
acid may be prepared in precisely the same way as you prepared
HC1, remembering that the sulfuric acid there used was somewhat
diluted. A very little HBr is oxidized by the H 2 SO 4 giving a trace
of free bromine and sulfur dioxide. Write the equation. But when
the gas is absorbed with water and the solution is distilled, the
trace of Br quickly passes off, and the sulfur and its compounds
that may be liberated are oxidized to sulfuric acid which remains
to the last in the distilling vess.el.

Hydriodic acid cannot be prepared by this method, since the
HI is almost completely oxidized to free iodine and water, and the
sulfuric acid is reduced to sulfurous acid and even to hydrogen sul-
fide.

Compare the degrees of stability of HC1, HBr, HI, and compare
these with their heats of formation by consulting a reference book.

34. Preparation of Hydriodic Acid: Arrange a test tube as in
fig. 10 high enough to permit heating and having a right angled de-
livery tube. Place in the dry test tube 5 grams powdered iodine and
on top of it 0.5 red phosphorous, shake to mix, put tube in place and
warm till the P and I react. When cool place delivery tube in
small flask or bottle and by means of the pinch cock drop into test
tube about 20 drops of water. Warm gently and collect the receiver
full of HI and stopper it. Now place the delivery tube in water in
test tube to absorb the gas, but have the tip of delivery tube just
above the surface of the water.

Prepare a little Cl in a test tube by warming a few crystals of
KC1O:; and a little con. HC1. Pour some of the Cl into the flask con-
taining the HI. What is set free?

Test the solution of HI in water with silver nitrate. What was
the action of the P and I? What was the action of this compound
and the water? What is hydrolysis. Write all equations.

This same method with some modifications is often used for
the preparation of hydrobromic acid. (See the text book for de-
scription.)

35. Powder a few crystals of iodine in a mortar, place it
in a test tube half full of water, and pass into the tube hydrogen
sulfide gas prepared as in 68. Have the delivery tube reach quite
to the bottom of the test tube. When all the iodine has disappeared
boil the solution for a time to expel the excess of hydrogen sulfide
and filter, several times if necessary to get rid of all the sulfur.



22 LABORATORY MANUAL OF GENERAL CHEMISTRY

Test the filtrate with blue litmus paper. Set the solution aside f.o
be used in the next experiment. Hydrogen sulfide here acts as a
reducing agent. Write the equation.

:W. Properties of Chlorine, Bromine, Iodine and Their Com-
pounds: Try to dissolve a little powdered iodine in water. Now
pour off most of the water, add a few crystals of sodium iodide and
shake. It is supposed the solution now- contains NaI 3 .

Try the solubility of I by pouring about Ic.c. of carbon disul-
fide upon a crystal of I in a test tube and shaking. Now add water
to the tube, shake and let carbon disulfide settle. In which liquid
is most of the iodine? Try the solubility of iodine also in alcohol
and in chloroform. Save the solutions of iodine.

Make a solution of starch by boiling about half a gram of
starch in a dish or beaker half full of water and with stirring.
Pour a little of the starch solution into a beaker of water, add a
little iodine solution. This is a good test for free iodine. Add a
little sodium iodide solution and a little of the starch solution to a
bleaker of water. To one portion add a little bromine water and to
the other chlorine water. Is iodine set free by the Cl and the Br?
To a solution of sodium bromide add chlorine water. Is bromine
set free? To concentrate the bromine and also to show its solu-
bility, to the liquid in the test tube add a little carbon disulfide,
shake and let the latter settle.

Arrange the three halogens in the order of the ability of each
to replace the others, and compare this order with that of the sta-
bility of their compounds with hydrogen.

To a little solution of iodine and to blue starch-iodine solution
add a solution of sodium thiosulfate till the colors disappear.

To show the reducing power of hydriodic acid make very di-
lute solutions of potassium dichromate and potassium permangan-
ate, add a little dilute sulfuric acid and then some of your solution
of hydriodic acid. The chromate and permanganate are reduced
and the solution is colored brown by iodine. For the same purpose
treat a little of a solution of sodium iodate, NaIO 3 , with dilute H 2 S0 4 and
add some of your solution of HI. Refer to a text book and write
the equations.

37. Tests for the Halogens: How may each of the halogens in
the free condition be recognized and tested for? (See 36). The
following applies to them in the form of soluble halides :

To three tubes containing respectively a little dilute HC1 or so-
lution of any chloride, solution of any bromide, solution of any
iodide, add a few drops of silver nitrate. Compare the colors of
the three silver halides. Try to dissolve a little of each with am-
thiosulfate. Try other portions with dilute nitric acid. Dissolve a



LABORATORY MANUAL OP GENERAL CHEMISTRY 23

aionium hydroxide. Try other portions with a solution of sodium
little of each with, potassium cyanide, KCN, being careful not to get it
on the hands.

38. Hydrofluoric Acid: Slowly and evenly heat a glass plate
over a burner flame. Rub over the surface a piece of bees-wax so
as to make a continuous film of the melted wax. When the wax has
hardened, write on the plate with a pointed file or knife, cutting
4uite through the wax. In a lead dish place a little ammonium
fluoride, or powdered calcium fluoride, moisten with con. sulfuric
acid. Cover the dish with plate, wax side down, and apply a low
heat to the dish so as not to melt the lead. After a few moments,
remove the wax and examine the glass.

To test for a fluoride place a little of it mixed with a little
sand, in a dry test tube, drop upon the mixture a little con. H 2 SO 4
and heat. While heating hold in the tube a wet stirring rod. Where
wet the rod will be covered with a jelly-like layer of silicic acid
Why cannot a solution of H 2 F 2 be kept in a glass bottle?

EQUIVALENT WEIGHTS.

39. Equivalent of Zinc: Set up the apparatus as shown in fig.
tO and prove that all joints are tight by placing water in the funnel
covering the end of the delivery tube with the wet finger and open-
ing the pinch cock. The water should not run down. The end of
the delivery tube should be bent upward and securely placed under
the jar. Use pure, bright granulated zinc.




Fig. 10.

Weigh with great care not less than 0.2 grams nor more than
0.25 grams of the zinc for every lOOc.c. that the jar or bottle will
hold. If an analytical balance is used one weighing will suffice.



^ I LABORATORY MANUAL OF GENERAL CHEMISTRY

Horn pan balances are not very accurate and rarely in exact equi-
librium. In this case weigh the zinc on one pan, then on the other
and take half the sum of the weights. What errors in the balance
will this practically eliminate? Place zinc in the test tube, fill
collecting jar completely with water, and add 15c.c. of con. HC1 to
the funnel. Let in all the acid and close the clamp. When all the
Zn is dissolved bring the level of the water in the jar to that in the
trough and securely place on the cover. Dry the outside of the jar
and weigh on the platform balance. Pill it completely with water
and weigh again. The difference in grams less the volume of acid
gives the volume of the hydrogen in cc. (V). Find the temperature of
the water in the trough (t), and the reading of the barometer (P). Cal-
culate the volume (V) to normal conditions by use of the formula,
V'=VX273X(P aq. tens, at t)-^(273-H) X760. Why? The weight
of H=V'X. 00009. The equivalent of zinc equals its weight divided by
the weight of HX 1.008, and its atomic weight equals twice this value.

40. Equivalents of Other Metals: Find the equivalent of one or
more of the following, using not more than the weights given for each
100 c.c. that the receiving vessel holds. Aluminium 0.07 gram; mag-
nesium, 0.08; .iron, 0.15. In the cases of aluminium and magnesium
it is better to place the test tube in a beaker of water to keep the tem-
perature down, and to use dilute acid. In the case of iron it may be
necessary to warm the con. HC1 used. Collect the hydrogen and pro-
ceed precisely as in the previous experiment.

41, Equivalent of Chlorine (a) : In normal times porcelain Gooch
crucibles are cheap, and if they are available this method should be
used; otherwise use (b).

Weigh accurately about 0.5 gram pure silver, preferably foil, place
in a beaker, add lOc.c. water and 5c.c. pure nitric acid, and cover with
clock glass. Warm if necessary, and after all is dissolved boil gently.
Wash under side of glass and the inner surface of beaker till beaker
contains about 75c.c. liquid, then add 20c.c. dilute hydrochloric acid
and stir. Set in dark place till ready to filter. In a clean Gooch cru-
cible make a mat of asbestos with aid of suction of the filtering pump
as shown by the Instructor. It should be thick enough so that you
cannot see light through it, dry for half an hour in oven at about 140
degrees, cool, in desiccator or on a clean surface and covered, twenty
minutes and weigh.

With suction pump filter off silver chloride into crucible as shown,
heat in oven one hour at about 140 degrees. Desiccate as before and
weigh. Find weight of silver chloride and thence chlorine, and cal-
culate the equivalent of chlorine if the equivalent of silver is 107.9.



LABORATORY MANUAL OF GENERAL CHEMISTRY 25

The equivalents of bromine and iodine may be determined in the
same way. Indirectly many other equivalents may be determined by
the method as the following problem illustrates:

If 3 grams potassium chloride be treated with an excess of silver
nitrate and the silver chloride weighs 5.773 grams, find the equivalent
of potassium, if that of chlorine is 35.5.

(b) Weigh accurately a small porcelain dish, place in it about
0.5 gram of silver foil and weigh again. Add to dish 5c.c. con. nitric
acid diluted with lOc.c. of water, cover with a watch glass. Give it
time and do not heat unless necessary. When all the metal is dis-
solved, with a small amount of water in a fine stream from the wash
bottle wash any spattered liquid from the under side of the watch
glass, into the dish. Add to the dish 20c.c> pure dilute HC1 and eva-
porate the liquid to complete dryness on a water bath. Heat the dish
in an oven for half an hour at about 125, or heat some distance above
the burner flame till the silver chloride begins to melt. When fully
cold weigh accurately the dish and contents, subtract from the weight
of the silver chloride the weight of the silver and find the equivalent
cf chlorine calling that of silver 107.9.

42. Equivalents of Copper and Other Heavy Metals : The equiva-
lents of copper and several other metals may be determined Toy con-
verting the weighed metal into nitrate with nitric acid, and decom-
posing the nitrate by heat, leaving the oxide.

Use accurately weighed copper foil or clean copper turnings, and
proceed the same as in 41 (b), but use no hydrochloric acid. Evapor-
ate to complete dryness, and heat high over a flame' with the watch
glass on the dish. Gradually lower the dish and when nearly all blue
color has disappeared, or all evidence of steam in the case of other
metals, remove the watch glass and apply the full capacity of the
burner for half an hour when there should remain a layer of black
copper oxide. Material spattered upon the glass must be washed back
into the cooled dish and the liquid must be evaporated again on the
water bath, and the dish strongly heated. Weigh when quite cold.

Prom the weight of the copper oxide subtract the weight of the
copper, and find the equivalent of copper calling oxygen 8. If 16 is
used for oxygen the number obtained for copper is its atomic weight.

MTROGEtf A1VD ITS COMPOUNDS.

43. Preparation of Mtrogen From the Air: Fill a pneumatic
trough with water till it rises, about % inch over the shelf. Place up-
on the shelf a small crucible or cupel and place in it as much red
phosphorus as will lie on a half inch of the end of a knife blade or
spatula. Ignite the P and at once place over the vessel and upon the
shelf a jar or wide mouth bottle. Let the jar remain till it is cool and



26



LABORATORY MANUAL OF GENERAL CHEMISTRY



(he white fumes have been absorbed. Note the height to which the
water has risen and estimate the ratio of the volume of oxygen which
has been consumed to the nitrogen which remains. Slip cover on the
jar, place it upright and test the gas remaining with a burning splint-
er. What other gases are mixed with the N thus obtained? Why does
not this method give accurate results as to the volume of oxygen in
air?

4-1. More Accurate Determination of Oxygen in Air: Arrange the
apparatus as shown in fig. 11. When all is adjusted, remove ihe test
tube, mix about 7 cc. of a solution of pyrogallol
with about the same volume of sodium hydroxide.
At once pour the liquid into the funnel. By open-
ing the clamp let the liquid down till it just
reaches the lower end of the tube. Attach the test
tube by inserting the stopper firmly, and opening
the clamp move it till it closes out of the way upon
the rubber and glass connecting tube. Move the
test tube to a horizontal position to expose the air
to more of the liquid surface. If the surface of
the liquid in the funnel threatens to lower into
the neck, add a little water. When you are sure
the liquid has ceased to enter the test tube, invert
the test tube and bring it up till the surfaces of the
liquid in test tube and funnel are at the same
Fig. 11. height, as shown by the dotted lines. Estimate, or

better, measure the lengths of the columns of the liquid in the test
tube and the gas which remains, Which represents oxygen and which
nitrogen? Find their ratio by volume in air.

15. Preparation of jVitrogen from Chemicals: Set up the appar-
atus as shown in fig. 12. The nitrogen is obtained by heating a solu-
tion of ammonium nitrite but since this substance is difficult to make
and to preserve, the same results may be obtained by heating a solu-
tion of ammonium chloride, NH 4 C1, and sodium nitrite, NaNO 2 . These
give in the solution the same groups, NH 4 and NO 2 , which form am-
monium nitrite, NH 4 NO 2 .

Put in the flask 10 grams of ammonium chloride, 10 of sodium ni-
trite and lOOc.c. of water. Heat and after the air has been expelled col-
lect the nitrogen in jars.

Light a bit of candle, place it upon the deflagration spoon and
lower it into a jar of the nitrogen. Lower burning phosphorus into
another jar.

Note the curious fact in this experiment that the oxygen of am-
monium nitrite oxidizes the hydrogen of the same compound; that is,
one part cf it acts as a reducing agent and the other as an oxidizing




LABORATORY MANUAL OF GENERAL CHEMISTRY




Fig. 12.

agent. Also, hereafter notice that whenever oxidation takes place witti
respect to one substance, reduction takes place at the same time with
regard to some other substance. Find illustrations of this under prep-
aration of chlorine, 24.

46. An analogous method may be used for the preparation of N by
heating an intimate mixture of ammonium chloride, 2 grams, and po-
tassium dichromate, 5 grams, instead of ammonium dichromate. The
method of heating and collecting is quite the same as that for oxygen
in 6.

4". Preparation of Ammonia, Place about a half gram of ammon-
ium chloride, ammonium sulfate, ammonium nitrate in three test
tubes. Add to each about 2c.c. of sodium hydroxide solution and
warm. Note odor in each case, and hold in each tube a strip of moist
turmeric paper. Repeat using about the same amounts of the am-
monium compounds, but mix each with about its own weight of slaked
lime. Formulate a general method of preparing ammonia.

Refer to a text-book for an account of calcium cyanamide, its
manufacture, hydrolysis, use, importance. In a test tube place about
a gram of the substance, barely moisten with water. Suspend in the
tube a strip of moist turmeric paper, corking the tube and thus hold-
ing the strip in place. Observe evidence of ammonia after an hour.

Set up the apparatus as in fig. 13 and provide the dry fountain
bottle as in 27. The collecting jars or bottles must be dry. Weigh and



28



LABORATORY MANUAL OF GENERAL CHEMISTRY




mix in mortar 10 grams each of
ammonium chloride and slaked
lime. Place on paper and slide
into iron tube. Protect the stop-
per of tube with wet cotton.
Heat the tube and collect two
bottles or jars of gas by the
downward displacement of air.
When full moist turmeric paper
held at the mouth of a jar will
be instantly turned brown.
While it is bottom upward
clamp cover on jar or cover
bottle with glass plate ani
place on desk bottom upward.
Fill the fountain bottle and pro-
duce a fountain as with HC1 in
Fig. 13. 27. Turn the delivery tube down

and place it in a test tube containing lOc.c. pure water so that the end
of the delivery tube shall reach just under the water. Observe ab-
( sorption of the ammonia and lower the delivery tube in the water as
necessary to absorb all the gas. Heat as long as ammonia seems to
come off, remove delivery tube from test tube then remove the lamp.
Observe odor of the solution of ammonia in the test tube. There
is evidently gaseous ammonia above the liquid. There is also am-
monia in solution, some ammonium hydroxide and some ionized am-
monium hydroxide.

48. Action of Acids and Ammonia; Neutralization: In a jar pour
a few c.c of con. HC1, wet the sides of the jar and pour out excess oi 7
liquid. Place over this the jar of ammonia gas, bottom upward, remove
cover, placing jars mouth to mouth. Mix by reversing the pair, placing
the jar with HC1 above. The fumes and the solid on walls of jars con-
sist of ammonium chloride, NH 4 C1, made by direct union of what? Try
a burning splinter in the remaining bottle of ammonia gas.

In this paragraph and in all other such cases do not dip test papers
into liquids, but take out a drop of the liquid with a stirring rod and
touch it to the paper. In a porcelain dish place lOc.c. of ammonium
hydroxide and neutralize with dilute nitric acid in just the same way
as sodium hydroxide was neutralized with HC1 in 28. Evaporate about
two-thirds of the liquid over a flame and complete the evaporation on
a water bath. Why on a water bath? Press dry the ammonium nitrate
between folds of filter paper.

Small quantities of ammonia may be tested for as directed in
Qualitative Analysis, Group V. Very small quantities are tested for



LABORATORY MANUAL OF GENERAL CHEMISTRY 29

with Nessler solution, which is a strongly alkaline solution of mercury
and potassium iodides. If at hand and to show the sensitiveness of the
test, fill a clean test tube nearly full of distilled water, and in another
tube of distilled water dissolve a granule of ammonium chloride as
large as a pin head. To each tube add about 2c.c. of Nessler solution.
In very dilute solutions the amounts of ammonia are in proportion to
the depths of color, and the test is much used to determine very small
amounts of ammonia in water.

49. Preparation of Nitrogen Monoxide (Nitrous Oxide): Set up
the apparatus as in fig. 12, but omit the thistle tube. Heat in the dry
flask 15 grams of ammonium nitrate, and regulate the heat so as to
control the flow of gas, which should be collected in three jars or bot-
tles. When through collecting remove the delivery tube from the
water, then remove the burner.

In one jar thrust a glowing splinter. In another lower burning
phosforus. Burn a piece of picture cord in the same way as in oxygen.
Write the equation and compare' it with the self-oxidation of ammonium
nitrite to form nitrogen.

50. Preparation of Xitrie Acid: Arrange the retort and receiving
flask as in the preparation of bromine, fig. 9, but retort and flask should
preferably be dry. Put into the retort as there described 20 grams of
sodium or potassium nitrate. Add through the tubulus of the retort
by means of a funnel 25c.c. of con. sulfuric acid. At once wash the
funnel and measuring cylinder. Let stand till acid and solid are in
contact throughout and then heat with a small flame, preferably of the
crown top. There is no need of cooling the receiving flask if the heat
applied is properly regulated. Turn down the flame if fumes escape
in considerable amount from the flask. Stop heating when the acid
comes over slowly and the liquid in the retort is clear and seems to
be viscid. What is the substance left in the retort? To remove it when
cool fill the retort nearly full of water and heat gently, best on a water
bath. Pour off solution, add fresh water and heat again. Repeat till
all is dissolved. If the cake of solid comes loose do not shake it about,
since the thin retort will be broken.

51. Oxidizing Action of Mtric Acid: Nitric acid, after free oxy-
gen, is the most important of all oxidizing agents and its oxidizing ac-
tion should be well understood.

When the very concentrated acid is heated a part of it breaks down
thus: (1) 2HNO 3 =H 2 O+2NO 2 +O. Whenever the more dilute acid is in
contact with something easily oxidized the reaction is likely to be:
(2) 2HNO 3 =H 2 O+2NO+3O. To illustrate, (a) heat a few drops of your
acid and note the red-brown gas given off. (b) Place a loose plug of
woolen yarn in the mouth of a test tube which contains about 2c.c. of
your acid, and boil the acid till the vapors ,set the wool on fire, (c)



30 LABORATORY MANUAL OF GENERAL CHEMISTRY

Heat a little sawdust in a dish till it begins to char and pour upon it
about Ic.c. of your acid, (d) Place about 3 grams of sugar in a flask
and 25 c.c. of con. nitric acid from the shelf. Heat till copious fumes
of N0 2 are formed. The sugar is mainly oxidized to oxalic acid. The
next experiment contains a good illustration of oxidation of metals
by' HNO :i .

In the most common case of oxidation with nitric acid the acid
itself is reduced to water and nitric oxide, NO. Oxidation and reduc-
tion, it will be remembered, go on together usually. In some cases the
reduction does not go so far. An instance is the reduction of a nitrate
to nitrite by heating with lead (see 54). In some cases the reduction
proceeds to the formation of hydroxyl-amine, HONH 2 , but more often
to ammonia. To illustrate this treat a few bits of aluminum in a test
tube with about 3 c.c. of sodium hydroxide, and add 2 drops of con.
nitric acid. Warm the tube and when the action becomes rapid note
odor of ammonia. Incline the tube and hdld in it moistened turmeric
paper without touching the glass. Here the hydrogen from the sodium
hydroxide and Al reduces the nitric acid to ammonia. Arrange in a
horizontal line in note book the successive reduction products of ni-
tric acid.

Aqua regia is a mixture of 1 part of con. nitric with 3 parts of con.
hydrochloric acid. Make about 1 cc. of the mixture, heat it and notice
chlorine given off. It will dissolve many substances that are attacked
by neither of the acids alone.

52. Action of Nitric Acid on Metals, Nitric Oxide: See in a text
book the electro-motive series, and the action of nitric acid on metals.

The very electro-positive metals will give some hydrogen with di-
lute nitric acid. Set up the apparatus to prepare H, but use a test
tube instead of the flask. Place in tube magnesium turnings. Dilute
con. HN0 3 by mixing 5 c.c. with 30 c.c. of water. Fill two test tubes
with water and have them ready to collect the gas. Put in the dilute
acid, about 5 c.c. at a time and after the air has been expelled collect
two test tubes of the gas. Test the gas for H. Note red gas in test
tube when air enters, using the second tube. Save the liquid in the
tube in which H was evolved. Repeat the experiment, using granulated
zinc instead of magnesium. Can you detect any H? Note red furnes of
nitrogen dioxide, N02, always formed when nitric oxide, NO, comes in
contact with air or oxygen. When the action is over pour off a little
liquid from the Zn and test it and the solution saved from the mag-
nesium for ammonia: To the liquid add NaOH in excess, hold a strip
of moist turmeric paper in the tube not letting it touch the glass and


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Online LibraryWalter Scott HendrixonA laboratory manual of general chemistry → online text (page 3 of 8)