· PREFAC E. THIS little book is intended to be used onl y with theassistance Of a teacher and as...
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Transcript of · PREFAC E. THIS little book is intended to be used onl y with theassistance Of a teacher and as...
AN INTRODUCTION TOTHESTUDY
0
Q U :A‘
_L l TA T l V E
CHEM CALANALYS S .
BY
J. T . M‘
C G ILL,
Ad'unct Professor Of C hem istry in Vanderbil t Univers ity .
PRIN TED FOR TH E AUTHOR .
PUBLIS HIN G H OUS E OF TH E M . E. C HURC H , S OUTH .
J. D . BARBEE ,AGEN T
,N A S HVIL LE ,
TEN N .
1889 .
PREFAC E .
THIS little book is intended to be used onl y with the assistance
Of a teacher and as an introduction to some full work on qualitaa
tive analysis, such as that Of Fresenius or Prescott.
Part I . contains such experiments as are found in late ele
mentary works on inorganic chem istry . These experiments are
designed to train the student in the construction and handling of
chemical apparatus,and to teach him how to Observe scientific
ally,reason upon
’
his Observations,and draw correct conclusions
from them . They are sel ected for the most part with special
reference to the analytical work that follows in Part II ., and in
clude the preparation Of many Of the reagents us ed in qualita
tive analysis and the examination of their properties . Part I.
may be Omitted by students who have taken a course in elementary chem istry, including experiments in the laboratory,such as Eliot and Storer’s
,Remsen’s
, orWil liams’s.
Part II . contains the S pec ial feature Of this book—i . e.,the ao
plication to qua litative analysis Of thatmethod Of teaching which ,ins tead Of imparting directly to the student the facts or lawswhich are the Ob'ect Of the study, leads him by questions and
sugges tions to work them out for himself. The use Of th is
method for two years in Vanderbilt Univers ity has led me toconclude that it prevents to a great extent the blind following Of
directions ,which the student is so liable to fall into in qualita
tive analysis, and that it al so imparts greater interest to thisstudy by requiring the student to test by practical examples the
correctness of the conclusions which he has arrived at as the result of his own investigations . It is not expected that the stu
dent will be able thus to construct full analytical tables which
237406
i i “ PBEFAC E .
may be used for very delicate or extensive analysis ; but he will
become prepared to use such tables in works on qualitative anal
ysis, not as a machine, but with an intelligent understanding of
the principles involved .
In the selection and description Of experiments I have used
freely the works of Eliot and Storer, Remsen, Williams, Hart,and others.
The author would be glad to have the benefit Of corrections or
suggestions thatmay occur to any onewho examines or uses the
book.
Vanderbil t Univers ity, July , 1889.
SUGGE S TION S TO TEAC H ERS .
1 . Have all material necessary for the exercise provided be
forehand convenient in the laboratory.
2. Discuss in the class-room with the students the work Of the
las t exercise ; state the correct results and inferences , or assign
the experiments when unsatisfactory for repetition,giving fuller
instructions ; give directions in regard to the experiments Of the
next exercise ; make drawings on the blackboard Of apparatus
to be used , or better have a model Of it at hand, and show howit is constructed ; indicate the method Of performing the experi
ments, but rarely perform the experiments yourself.3. Caution the student in the use Of dangerous chemicals and
the performance Of experiments in which accidents are liable tooccur. In my experience more accidents have happened from
the careless use Of concentrated sulphuric acid than in any other
way.
4. Require the pupils at the close Of each exercise to deposit
their note-books at some place where you can get them for ex
amination . A case Of “pigeon-holes numbered to correspond
with the numbers Of the desks will be found convenient as a
place Of deposit for note-books,and
,later in the course
,for notes
on analyticalwork and compounds for analysis .
DIRE C TIONS TO PUPILS .
1 . Before beginning an experiment read the directions through,
and provide yourselfwith every thing whi ch you can foresee tobe necessary to complete the experiment.
6 EXPLAN ATION S .
2. Direct special attention to constructing neat and well-fittingapparatus
,and keep every thing about your desk clean .
3. At the close of an experiment record in your note-book im
mediately (1) the material employed, a brief description of the
apparatus used,the method Of procedure ; (2) What takes place
(3) the inferences you draw or what you haVe learned from the
experiment.
Leave ample space in your note-bo'
ok for making corrections
and additions without erasing any of thefirst record.
EXPLANATIONS .
1 . Dilute acid is intended unless cone. is prefixed .
2. When a formula is given without the name of the com
pound the name and formula will be found in some previous
experiment.3. An interrogation point inclosed in parentheses at the close
Of a statement means that the student is expected to determineby
‘ experiment whether the statement be true.
4. Weighed quantities of substances are used approximately .
except when the expression “weigh out ” occurs.
CONTENTS .
PART I. EXPERIM EN TS IN GEN ERALC H EM IS TRY .
EXPERIM EN T
The Bunsen Burner
Charcoal as a Reducing Agent.S odium N itrate as an Oxidizing AgentHeating on Asbestos ; on Charcoal .Ri sion on Platinum Wire ; on Platinum FoilHeating and Bending Glass .Evaporation
,Distillation, Solution
Effect Of Solutions upon LitmusDilute AcidsAmmoniaHydrochloric AcidAmmonium ChlorideSalts from an Acid and an HydroxideDecomposition OfMercuric Oxide .
Oxides and Hydroxides Of the Alkali MetalsOxides and Hydroxides Of the Alkaline Earth Metals .Oxides OfMagnes ium
,Z inc
,Tin
,and Aluminium
Salts from an Acid and a Metallic OxideSulphur .
Oxides Of Sulphur . .
Phosphorus PentoxideSodium Sulphide. .
Iron Sulphide ; Hydrogen SulphideHydrogen by the Action Of a Metal on WaterHydrogen by the Action Of a Metal on an AcidOxygen .
N itrogen .
8 C ON TEN T S .
EXPERIM EN T
33.
34.
35 .
36.
37.
38 .
N itrous OxideN itric OxideN itric AcidHydrochloric AcidAqua Regia . .
Carbon Dioxide
PART II. EXPERIM EN TS IN QUALITATIVE AN ALY S IS .
39 .
40.
41 .
42.
43.
44.
45 .
46.
47.
48 .
TH E M ETAL S .
Separation Of the Metals into GroupsGroup I . Hydrochloric Acid GroupGroup II . Hydrogen Sulphide GroupGroup III . Ammonium Sulphide GroupPrecautions in the Separation Of Groups I.
,II .
,and III .
Group IV. Ammonium Carbonate GroupGroup V. Sodium PhOS phate GroupGroup VI. Soluble GroupSeparation Of Groups IV.
,V.
,and VI
Some Special Cases under Group III
TH E AC I DS .
In o rg an ic Ac id s .
Barium Chloride GroupSilver N itrate GroupSilicic Acid .
H ydrofluoric AcidBoric Acid .
Sulphurous and Hyposulphurous AcidsChloric Acid .
O rg an ic Ac id s .
Test Of an Organic CompoundConc. Sulphuric Acid on Organic AcidsOxalic
,Tartaric
,Citric
,and Malic Acids
Succinic, Benzoic, Formic, and Acetic AcidsOrganic Compounds Insoluble in Water .
PA R T I .
EXPERIM ENTS iN GEN ERALC H EM ISTRY .
LE N GTH .
1 . Estimate by the eye 1 dm . Close 7
the book and lay Off this distance on aslip Of paper ; divide it into cm . ; div ide1 cm . into mm . Compare the scale you
have made w ith the model . Repeat thisexperiment several t imes . Estimate thedimensions Of glass tubing
,test-tubes
etc .
VO LUM E .
2. Pour 25 cc . Of water into a smallbeaker . Mark the level Of the water bymeans of a gummed label . Graduate alarger beaker to 100
,200
,and 500 cc .
,
and a test-tube to 5,10
,and 25 cc . E s
timate the capacity of different vesselsat your desk .
W E IGHT .
3. (a) Weigh the small graduatedbeaker . Pour into it 25 cc . Of distilledwater and weigh . Pour out the water
,
wipe the beaker perfectly dry,and
weigh in it 25 cc . of cone. sulphuricacid . What is the specific gravity Ofconc . sulphuric acid ? H ow many cc .
2
10 EXPERIMEN T S IN
conc . sulphuric acid weigh 25 g . ? How many cc . Of al
cohol,specific grav rty weigh 50 g . ?
(6) Balance two filter papers On the scales . WeighOut 1 g. Of sodium chloride ( common salt) , 1 g . Of leadchloride (PbC lz) , 1 g. Of calcium phosphate ( C aaPOQ.
By subdividing these,estimate the amount Of each that
would weigh g .
,g . Preserve the 1 g . weights
of the above substances for future use .
TH E BU N SEN BUR N ER .
4. (a) L ight and H eat of F lame—Examine the structure Of a Bunsen burner. Compare the flame Of theburner when the valve is open with the flame when thevalve is closed . In which flame will a platinum wireglow more brightly ? Which flame gives more light ?wh ich more heat ? A deposit Of carbon is made on ap iece Of porcelain held in one Of these flames Can
you burn the carbon Off ? Rub together two pieces Ofcharcoal so that a fine dust falls into the colorless flame .From the above experiments what inferences could youdraw in regard to the causes Of light and heat in flame ?
(6) Form of F lame—Make draw ings Of the flames ofthe Bunsen burner. Hold a platinum wire across theflame (try both flames) at different heights above theburner. Try a similar experiment with a splinter ; witha glass rod . Thrust the sulphur end Of a match quicklyinto the center Of the flame . Hold a piece Of paper horizontal ly in the flame and withdraw it 'ust before itwould ignite . U se wire gauze instead Of paper
,om it
ting the withdrawal . What do you learn from these ex
periments ?
TEMPERATURE OF IG N IT IO N .
5 . Pour 1 cc . Of carbon bisulphide ( C S 2) into a porcelaincrucible . Can you ignite it by thrusting a heated glass or
GEN ERAL C H EM I S TRY . 11
Iron rod into the mouth Of the crucible ? Bring the heatedrod in contact with a little sulphur. Can you ignite coalgas with the heated rod Suspend a spiral Of platinumwire in a small flame above a burner. When the platinum is at a white heat put out the flame with a suddenpuff of air . Expla in the result . L ower a piece of wiregauze horizontally into the flame Of a burner. Can youthus extinguish a small flame ? Hold a piece Of wiregauze horizontally three or four cm . above a burner ;turn on the gas and try to light it above the gauze . If
you succeed , gradually raise the gauze . What is theOffice of a w ire gauze placed under vessels that are beingheated
TH E BLOW -P IPE AND BLAST- LAM P .
6. Examine the structure Of the“blow-pipe ; the blastlamp . Compare their flames with the burner flame .
Practice with the blow-pipe until you can blow a steadystream Of air for two minutes .
CHAR C OAL A S A REDUC I N G AGEN T .
7. M ix in a mortar 1 g . Of lead carbonate w ith a sufficient quantity Of powdered charcoal to nearly fill asmall porcelain crucible . Cover the crucible and heatit over the blast- lamp for three minutes . Pour the contents Of the crucible into a mortar
,rub with water
,pour
Off the charcoal and water and look for scales Of lead inthe bottom Of the mortar.
SO D IUM N ITRATE ( N a N O a) A S AN O X I D IZ I N G AGEN T.
8 . Fill a porcelain crucible half-full Of N aN O3 and heatuntil the salt fuses . Throw powdered charcoal in smallquantities upon the fused mass . The charcoal is Oxid
12 EXPERIMEN T S IN
ized,and burns
,form ing carbon dioxide gas . The chem
ical action that takes placemay be expressed as follows :C arbon (charcoal ) and oxygen form carbon dioxide.
C 0 2
Potassium nitrate (KN Os) and potassium chlorate
(KC lOs) are likewise used as ox idizing agents .
HEAT I N G ON ASBESTO S ; ON C HAR C OAL .
9 . (a) Place g . Of lead carbonate on a slip Of ashestos
,and heat it in the yellow or in the inner flame of
the blow-pipe unti l a globule Of lead is obtained . Heatthe globule in the poInt Of the blow-p ipe flame . OxideOf lead is formed . Reduce the Oxide to lead . Sim ilarexperiments may be tried with Zn, Sn, Cu, Sb, Bi, ortheir compounds .
(6) Try to reduce some Of these compounds to the metal lic state by heating them on a p iece Of charcoal before the blow-pipe . Is the reduction effected more easilyon asbestos or charcoal ?
FUS IO N ON PLAT I N UM W I RE ; ON PLAT I N UM FO I L .
Borax,sodium metaphosphate
,and sodium carbonate
are Often used as fluxes in heating substances on platinum wire
,platinum foil
,charcoal
,or in crucibles . N i
trates Of sodium or Of potassium are sometimes usedm ixed with these . Platinum must not be used when thesubstance may be reduced to a metallic state .
10. (a) Make a transparent sodium metaphosphatebead in a loop On the end Of a platinum wire
,bring it
while hot in contact with a small quantity Of powderedmanganese carbonate
,heat in the oxidizing
,then in the
reducing flame Of either the Bunsen burner or the blowpipe . Observe the change in color. Try a similar ex
periment with a borax bead and cobalt carbonate .
GEN ERAL C H EM I S TRY . 13
M ix g . Of manganese carbonate with g . Of
sodium carbonate and heat on a platinum foil .
H EAT I N G AND BE N D I N G GLASS .
The operations should first be performed by the
teacher in the presence Of the class .
11 . Round the ends Of some glass rods in the hottestpart Of the flame Of the Bunsen burner. Make half adozen ignition tubes by melting in two at the middlep ieces of glass tub ing about 15 cm . long. Bend eighttubes at right angles
,making six Of them with the limbs 6
and 9 cm .
,one 25 and 10 cm .
,and one 35 and 8 cm . long.
Round the sharp edges Of the ends Of these in the flame .
EVAPO RAT IO N , D IST I LLAT IO N , SO LUT IO N .
12. (a) Dissolve 1 g . N aC l in 20 cc . water. Evaporatehalf Of the solution to dryness in a porcelain dish . Whatremains Taste it . Distill the remainder Of the solution
,
heating carefully until the distillate amounts to severalcc . (The distillate is the part that passes over.) Evaporate the distill ate to dryness . What remains A con
v enient apparatus for this purpose may be made by connecting two large test-tubes by a tube 15 cm . long
,curved
so that the test-tubes set at about right angles to eachother. A groove in the side Of the stopper Of the tubeused to collect the distillate will perm it the escape Of nucondensed vapor.
(6) Place g. powdered barium sulphate (BaS O,) in atest-tube . Pour into the test-tube 1 cc . water. Doesthe BaS O, appear to di ssolve ? Add 5 cc . water
,boil
,
and filter. Evaporate a port ion Of the filtrate—21a ,the
part that runs through . Is BaS O4soluble in water
(c) Weigh out g . calcium sulphate Shakeit upw ith 5 cc . water
,and let it stand a few minutes . If
14 EXPERIMEN T S IN
it does not all dissolve,add more water
,shake
,and let
it stand . Determine in how many times its weight Ofcold water C aS O4 is soluble, 1 cc . water weigh ing 1 g .
How could the exact solub ility Of C aS O, be determinedwithout adding a sufficient amount Of water to dissolvethe whole Of the weighed amount taken ? Save 10 cc .Of the solution for 12 (e) and 12 (f) .
(d) Make a strong solution Of g . powdered crystalline lead chloride in hot water. 0001the solution . Explainthe result . Does al l Of the lead chloride crystallize out ?
(e) Add 10 cc . alcohol to 5 cc . C aS O4 solution .
(f Add 10 cc . alcohol to a strong solution of sodiumchloride
,filter
,and dry the precipitate . Is it sodium
chloride ?
(9) Add conc . hydrochloric acid to a strong solutionOf sodium chloride
,filter
,and evaporate Off the acid
from the residue . What is th is residue ?
(h) The same as (g) , using barium chloride instead Ofsodium chloride .
( i) Dissolve 1 g . Of calcium phosphate (bone ash) inhydrochloric acid
,and evaporate to dryness until the res
iduo does not smell Of acid . IS calcium phosphate at
tacked by the acid,or simply held in solution ?
') Add solid sod ium carbonate to 1 cc . hydrochloricacid until effervescence ceases . IS the gas that comesoff combustible ? Evaporate the solut ion to dryness .Compare the taste Of the residue with that Of the sodium carbonatc . How does th is solution differ from thepreceding ?
(k) Dissolve sodium carbonate in water, evaporate,and examine the residue .
EFFECT O F SO LUTIO N S UPO N LiT M U S .
13. Test the reaction Of all the solutions at your desk
GEN ERAL C H EM I S TRY . 15
to red and to blue litmus paper. Those turning blue tored are said to have an acid reaction , those turning red
to blue an alkaline reaction,and those not chang ing the
color Of either red or blue litmus a neutral reaction .
D I LUTE A C I DS .
14. (a) Pour 5 cc . conc . sulphuric acid into 25 cc . wa
ter. Notice the rise in temperature . Th is is the strengthOf the dilute sulphuric acid at your desk . Water mustnever be poured into conc . sulphur ic acid . Why not ?
(b) Pour 5 cc . conc . hydrochloric acid into 25 cc . water. This is the strength Of the dilute hydrochloric acidat your desk .
(0) Pour 5 cc . cone. nitric acid into 25 cc . water . Thisis the strength Of the dilute n itric acid at your desk .
(d) D ilute with water 5 cc . Of each Of the above solutions (a) , (b) , (o) , to 500 co
,and compare the acidity by
tasting .
AMMO N IA .
15 . (a) Distill some sodium hydrate solution . Testthe distillate with litmus paper ; the residue .
(6) Pour 25 cc . cone. ammonia into a small flask,
through the stopper Of which is inserted a straight glasstube 25 cm . long
,Open at both ends . Hang a test-tube or
small flask over the end of the tube . Warm the ammonia . When the test-tube is full Of the gas, which maybe known by the smell Of ammonia at its mouth
,
take it Off,keep ing its mouth downward
,and dip the
end Of it under the surface Of the water. Explain whathappens . Is ammonia gas combust ible ? IS it lighter orheav ier
s
than air ? What is the color Of the gas ? Is itmore soluble in cold or hot water ? Save 100 cc . Of the
gas in a closely-stoppered,inverted bottle for 17 (a) . A
gas is said to be collected by upward displacement when
16 EXPERIMEN T S IN
collected as in this experiment . Ammonia gas has theformula N H s. Its solution in water is called ammonia
(also ammonium hydroxide and ammonium hydrate) , andhas the formula N H ,OH ; but in reactions it is Oftenwritten N H s.
HYDRO C H LO R IC A C I D .
16. Heat 25 cc . Of cone. hydrochloric acid in a smallflask under a hOOd. A gas is given Off. Collect it byletting the outlet tube extend downward almost to thebottom Of the receiving vessel which may be covered bya piece Of paper. A piece Of moistened blue litmus pa
per at the point where the outlet tube pierces the papercovering will indicate when the vessel is filled by turningred . The gas is thus collected by downward displacement . Fill several bottles and cover their months withwatch-glasses or glass plates . Invert one Of the bottlesin water
,and remove the glass covering. Is the ga
more soluble in cold or hot water ? IS it combustible ?IS it lighter or heavier than air ? Hydrochloric acid gashas the formula H C l . Its solution in water is called bydrochloric acid, or muriatic acid, and in reactions is alsowritten H C I.
AMMO N I UM C H LO R I DE
17. (a) Bring the mouth Of the bottle Of ammonia gassaved from experiment 15 over a bottle Of hydrochloric
acid gas, and m ix the gases .Evaporate to dryness 10 cc . Of ammonium chloride
solution,and compare the residue with the solid product
Obtained by m ixing hydrochloric acid gas and ammonia
gas, ( 1) by tasting, (2) by heating On a piece Of platinumfoil .
(0) Suspend a drop Of concentrated hydrochloric acidon the end Of a glass rod
,and bring it near the mouth Of
a bottle Of ammonia . What is the smoke that is formed ?
18 EXPERIMEN T S IN
O X I DES AND HYDRO X I DES O F TH E ALKAL I M ETALS .
20. (a) Place in a small porcelain dish a piece Ofpotassium the Size Of a pea . The change Of color at thesurface on remaining in the air is due to the formationOf the Oxide of potassium . (Are
'
gold,si lver
,tin
,zinc
,
iron oxidized thus ?) Heat gently. The oxidation takesplace more rapidly. After the potassium is completelyOxidized allow it to cool
,and then add a few drops Of
water. What causes the rise in temperature ? Test thesolution with litmus paper. What does the solution contain ? KzO H ZO
Perform a similar experiment with sodium .
Na20 H zO The teacher should furnish for ex
periments in which they are required K,Na
,and P al
ready cut into p ieces Of the proper size .
O X I DES A N D HYDRO X I DES O F T H E ALKAL I N EEARTH M ETALS .
21 . (a) Is calcium carbonate ( C aC Os) soluble in water ?Try a particle of it . Test the liquid with litmus paper.Heat 5 g . C aC O, in an open porcelain crucible over ablast-lamp for several m inutes . C aC O3 C aO 00 2.
Pour a portion Of the contents Of the crucible intoa porcelain dish
,and when that in the dish has cooled
pour On it a little water. What causes the heat ? Caloium hydroxide is formed : C aO H zO C a(OH ) 2.
Test with litmus paper. The solution Of C a(OH ) 2 inwater is called lime-water. Prove that C a(OH ) 2 is soluble in water . Is it more soluble than KOH or NaOH ?
(b) Rub some moist C a(OH ) 2 with a particle Of anyammonium salt . What is given Off ? Write the reac
tion . Heat moist C a(OH ) 2 with an ammonium salt .Ammonia gas for making ammonium hydroxide (ammonia) is thus manufactured . Will KOH or N aOH de
GEN ERAL C H EM IS TRY . 19
compose an ammonium salt ? How can you distinguishan ammonium compound from other compounds ?
O XI DES O F MAG N ES I UM , Z I N C , T IN , ANDALUM I N I UM .
22. Heat a platinum wire . There is no chemicalchange . Heat a magnesium wire . Tilt the burner toone side so that the magnesium oxide formed in the com1
bustion may be caught in a dish . Moisten the oxidewith water and test with litmus paper . Is it soluble inwater ? in hydrochloric acid ? Does hydrochloric acidform a new compound with it or merely hold it in solution as in the case Of calcium phosphate in 12 (i) ? Is
iron easily oxidized ? Does oxide Of iron part with ox
ygen so easily as H gO ? Is It soluble in water ? Whatwould you say Of Z nO
,S nO,,
Al 03 in these respects ?It is seen from experiments 20 and 21 that the oxides
Of the alkal i metals and Of the alkal ine earthmetals unite
with water to form soluble hydroxides . The oxides ofmost Of the other metals do not combine directly with water
,but under certain conditions they form hydroxides
almost insoluble in water. The hydroxides of the metalsare called bases . They unite with acids to form salts
SALTS FRO M AN A C I D AND A M ETALL IC O X I DE .
23. (a) D issolve 1 g . Of zinc oxide in dilute H C I.Evaporate to dryness . The residue is a salt soluble inwater. Z nO 2H C I Z nC l2 H ,O . By dissolving a
metal lic oxide in an acid a salt is formed .
(6) D issolve copper Oxide ( C uO) in H,SO, . Write thereaction . Evaporate till a drop Of the solution placedOn a watch-glass will deposit crystals On cooling . S et
the solution aside to cool .
(0) Heat in a crucible or dish 1 g . crystalline coppersulphate . C uS O 5H ,O C uS O4 5H ,O .
20 EXPERIMEN T S IN
SULPHUR .
(a) Heat slowly 15 g. S in a test-tube . Continueto heat until it boils
,noting the changes which the S
undergoes . Pour the melted S in a fine stream into adish Of water. Examine the S that has been poured
into the water. Will it retain its plastic cond ition ifkept under water ? in the Open air ?
(b) Melt in a crucible or in a small beaker 25 g . rollsulphur. Let it cool slowly and quietly . When a thincrust has formed on the surface
,make a hole in the crust
and pour out the liquid S . Examine the crystals that
remain in the vessel .
(c) Pour 3 cc . carbon bisulphide ( C S 2) upon 1 g. S ina test-tube . Close the mouth Of the test-tube and shakefor a few moments . When the S has dissolved pour thesolution into a watch-glass . Examine the crystals thatform as the C S 2 evaporates .
(d) Add a few drops of cone . H C Ito 5 cc . ammoniumsulphide . Sulphur separates from the liquid in a finelydivided state .
O X I DES OF SU LPHUR .
25 . Make a hollow in the end of a p iece Of chalk .
Place in it some sulphur. Ignite the sulphur and sus
pend it in a large bottle . The Odor is that Of sulphurousanhydride formed by the oxidation Of the sulphur.S C 2
= S O, . Pour some water into the bottle . Testthe solution w ith litmus paper. S O2 is an acid-formingoxide . The acid formed is sulphurous acid . SO , H 20
H 2S 03. A higher oxide Of sulphur ( S O3) forms w ithwater sulphuric acid . H ,O S O3 H 2S 04.
P H O S PH O RU S PEN TO X I DE .
26. Repeat experiment 25,using instead Of S a p iece
Of dry phosphorus half the size Of a pea . The wh ite v a
GEN ERAL C H EM I S TRY . 21
per is phosphorus pentoxide With water it formsphosphoric acid . P20 5 3H ,O 2H,PO, . What salt
is formed by neutraliz ing this acid with N aOH ? withWrite the react ions .
The oxides Of most O f the non-metallic elements areacid-forming Oxides— i. e.
,unite with water to form acids
(25 and
SO D I UM SULPH I DE .
Sulphur forms many compounds analogous to those Ofoxygen . Recurring to experiment 20
,perform the fol
lowing experiments and write the react ions :27. (a) Cover a p iece of sodium in a porcelain crucible
with sulphur, put on the crucible lid, and warm gently .
When the crucible has cooled dissolve a port ion Of itscontents in a few drops Of water
,reserving the remainder
for 27 Test the solution with litmus paper. Thesolution contains sodium sulphide (Na,S ) .
‘
Plaee a dropOf it On a Silver coin . The dark substance is Silver sul
phide (AggS ) . Rub the spot with a little potassium cy
anide. (Potassium cyanide is very poisonous .) Add afew drops Of the Na,S solution to a solution of silver nitrate in a test' tube
,then gradually add potassium cyanide
solution .
(6) Try the effect Of barium sulphate on a S ilver coin ;Of sodium carbonate . Heat on charcoal before the blowp ipe a mixture Of sodium carbonate and barium sulphate .
Test the melted mass as the product Of sodium and sulphur was tested in 27 (a) . How can the presence Of sulphur be detected in an insoluble compound ?
(0) Add H C Ito the sodium sulphide reserved from 27
(a) until the solution is neutral to litmus . Compare w ith18 and write the reaction . The gas given Off is hydrogen sulphide What remains in solution ?
22 EXPERIMEN T S IN
I RO N SULPH I DE ; HYDRO GEN SU LPH I DE .
28 . (a) Examine fine iron filings and powdered sulphuras follows : ( 1) With a magnifying-glass, (2) by bringing a magnet near them
, (3) solubility in water, (4) solubility in carbon bisulphide, (4) solubility in acid .
M ix thoroughly 2 g. Of iron filings with 2 g. Ofsulphur. Examine small portions Of the mixture as in28 (a) .
(0) Pour the m ixture into a dry test-tube, and heat tillthe m ixture glows . When the glowing has ceased takeout the mass
,and exam ine small portions as in 28 (a) .
(d) Put the remainder Of the iron sulphide into a testtube
,add ‘H 2S 0 4,
and test the properties Of the gas.
What remains In solution in the test-tube ? Write thereaction . The solution Of the gas in water is the hydrogen sulph ide at your desk . The solution Of ammoniumsulphide at your desk is made by saturating a solutionOf ammonia with hydrogen sulphide gas
,or a solution Of
hydrogen sulphide with ammonia gas.
(e) Try the effect Of acids, dilute and strong, upon hydrogen sulphide solution ; upon ammonium sulph ide S Olution .
(f ) Try the effect Of a few drops of hydrogen sul
phide on a solution Of silver n itrate ; lead acetate . Try
ammonium sulphide on these solutions .
HYDRO GEN BY TH E ACT IO N OF A M ETAL ONWATER .
29 . (a) Throw a piece Of potassium the size Of a grainOf wheat on water. Notice the color Of the flame .
What burns ? Test the water with litmus paper.
(5) Throw a piece of sodium as large as a pea on somewater in a porcelain crucible . Wrap a p iece Of sodiumin a piece Of thin paper and throw it Onthe water in thecrucible . Test the water w ith litmus paper. Evaporate
GEN ERAL C H EM I S TRY . 23
to dryness and compare the residue with that Obtainedby evaporating some solution Of sodium hydroxide .
Neutral ize with H C I. What is formed ? D id the se
dium get oxygen from the air in burning on the water ?
(0) Fi ll a test-tube with water and invert it in a di shOf water. Take care that no bubble Of air remains inthe tube . At the close Of the experiments with hydrogen (30) explain the reason Of this precaution . Nowtake a small p iece Of dry sodium on the point of a rat
tail file and thrust it under the mouth Of the test-tube S Othat the sodium will rise in it . Close the mouth of thetest-tube with the thumb
,and open it near a flame . The
gas that burns is hydrogen . Test the water in the dishwith litmus paper. What elements does this experimentprove water to contain ?Water is decomposed by iron at a high temperature .Water may be decomposed by a current Of electric ity
,
and the volume Of hydrogen and oxygen measured . Thevolume Of the hydrogen is then found to be twice thatOf the oxygen . The action Of an acid on a metall ic oxidehas been found tO result in the formation Of a salt andwater (25)— e. g.
,Z nO H,SO, Z nS O4
E ,O . Let
us try the effects Of an acid On a metal .
HYDRO GE N BY T H E A
g'
gl
lgN O F A M ETAL O N A N
30. Pour H,SO4 on some pieces Of Zn in a small
flask or large test-tube . Collect the gas over water in
test-tubes at first,and ignite the gas as in 29 (c) . What
dO you infer from the way the gas first collected burns ?
What precautions must be Observed in making this gas
When the gas has been coming Off for several m inutes,
and when collected in a test-tube is found tO burn qu iotly, collect several bottles Of the gas and try the following experiments
0
24 EXPERIMEN T S IN
(a) Thrust a lighted taper into a bottle Of the gasheld mouth downward (why not mouth upward ?) withdraw the taper ; insert again while the gas is burning .
(b) Fill a small bottle with air and hydrogen in thepreportion of three tO one by volume . Let the mixturestand for awhile
,and then bring the mouth Of the bottle
near a flame . H OW could hydrogen be emptied fromone vessel into another in the air ? under water ? Could
hydrogen be collected by downward displacement in theair ? by upward displacement ? Why not collect it thusinstead Of over water ? Why can you not collect ammonia gas or hydrochloric acid gas over water ?
(0) Arrange an apparatus for burning hydrogen in a
'et . Does the flame afford much light ? much heat ?What is formed in the combustion ? HOld a dry beakerover the hydrogen 'et . What i s deposited On the innersurface Of the beaker ? What remains in solution in theflask after making the hydrogen ? Write the reaction .
C an other metals and other acids be used in making hydrogen ? Try several in test-tubes . By dissolving a
metal in an acid a salt is formed .
O XYGE N .
We have seen that mercuric oxide when heated decomposes into mercury and oxygen : H gO Hg 0 .
Oxygen can be made also by heating some other oxidesrich in oxygen . Black Oxide Of manganese (M n0 2)when heated decomposes as follows : 3M nO2 M 1130 ,
0 2. Oxygen is generally made by heating potassiumchlorate (KC lOs) . By mixing with the KCIQ3 someM nO2 or Fe,O, the oxygen comes Off at a lower temperature and more regularly. The M nO2 should be heatedto redness to insure the destruction of any impurity Of
organic matter before using it to mix with KC lOs.
26 EXPERIMEN T S IN
Of filter paper a piece Of phosphorus half the size of apea
,and place it in the crucible . Set fire tO the phospho
rus and lower over it carefully a large-mouthed bottle .
When the P20 5 fumes produced by the combustion havebeen absorbed by the water
,mark with a label the level
of the water in the bottle . The gas remaining in thebottle is n itrogen . Close the mouth of the bottle
,and
take it out Of the water.
(6) Pour some clear lime-water into the bottle , andShake it up with the nitrogen . Does nitrogen renderlime-water m ilky ? Is n itrogen combustible ? Does itsupport combustion ? Measure the capacity Of the bottle when filled up to the label . Supposing the atmosphereto consi st Of oxygen and nitrogen gases
,what percentage
by volume is oxygen nitrogen ?
(c) Nitrogen may be made by heating a cone. solution
Of ammonium nitrate (N H ,N O2 N2 2H 20 ) ; or byheating a mixture Of potassium bichromate and ammonium chloride 2N H ,C I 2KC l C r20 3
4H zO N 2) .
N ITRO US O X I DE .
33. Heat 10 g . Of ammonium nitrate in a large testtube until the salt melts ; then heat slowly, but continuously . Collect the gas over warm water . Why not
over cold water ? If any white fumes appear in makingthe gas, account for them . The gas thus prepared is ni
trogen monoxide,or nitrous oxide (N2O) . Write the re
action .
(a) Insert a glowing splinter into a bottle Of the gas.
(5) Burn some sulphur in a bottle Of the gas. Doesthe sulphur burn exactly as sulphur in oxygen ?
(0) Invert a bottle Of the gas in a dish Of cold water .
If the gas does not all dissolve, test the residual gas witha glowing splinter.
GE N ERAL C H EM IS TRY . 27
(d) Incline a bottle Of the gas standing over wateruntil some bubbles Of air enter . Is any change apparent ?
Save a bottle Of nitrous oxide for 34 (e) .
N ITR I C O X I DE .
34 . Mix 5 cc . Of water with 5 cc . Of cone. H N O,
Pour this diluted acid Over 5 g . Of copper turnings in asmall flask . The react ion is 3Cu 8HNO3
4H ,O 2NO (nitric oxide, or nitrogen dioxide) . Theformula is also written N2O2. Collect the gas overwater.
(a) When several bottles Of the gas have been col
lected let the remainder Of the gas pass into a solution Offerrous sulphate The nitric oxide is absorbedby the solution tO form FeS O,
N O .
(b) Incline a bott le Of nitric oxide standing Over water unt il a few bubbles Of air enter . Nitrogen tetroxideis formed
,wri tten NO, or N,O, . Test with litmus paper
the water in the bottle . 2NO H ,O H N O,
H N O, The nitrous acid (HNO ,) is at once decomposedat ordinary temperatures into nitric oxide and nitricacid . 3NO , H ,O ZH N O, NO .
Account for the red fumes which were at first seen inthe test-tube in preparing nitric oxide . What becameOf them ?
(0) Mix a small port ion Of the dark solution (a) w ithcone. H,SO, ,
keeping the mixture cool .
(d) Pour the remainder of the dark solution into atest' tube and heat . Is any gas given Off ?
(e) H ow can oxygen,nitrous oxide
,and nitric oxide
be distinguished from one another.
N ITR I C A C I D .
35 . (a) Put 5 g . Of sodium nitrate into a large test
28 EXPERIMEN T S IN
tube ; cover it with cone. H ,SO, ; heat, collecting thedistillate in a test-tube cooled in water. 2N aN O3
H 2804 N azS O4 2H N 0 3. N itric acid is manufactured from these materials .
(6) Take 5 cc . cold dilute HNO3 in a test-tube . In
cline the test' tube and add carefully an equal volume ofcone. solution Of FeS O,,
so that the FeS O4 solution willform a layer above the H N O, Set the tube aside . A
dark ring should form where the liquids are in contact .
(0) Add to 3 cc . Of a weak solution Of any nitrate anequal volume of cone. H,SO, . Allow the mixture tocool . Now add conc . solution Of FeS O, as in 35 (b) .What is the test for a nitrate ? Why should the mixture of H ZS O4 and the solution to be tested for HNO3 be
cooled before the addition Of the FeS O, ?
Pour a few drops of cone. HNO3 on some pieces Oftin foil in a crucible . Wash the wh ite powder Obtainedseveral times with water
,decanting the liquid . Then
place the white powder On a fi lter,and wash until the
washings contain no H N Os. (H ow can the absence ofHNO3 be proved ?) Prove that the white powder is nota n itrate by applying the test for a n itrate . All nitratesare soluble in water. The tin is oxidized by the H N O,
4HNO3 2H ,O 2N,O, 0 2 ; Sn 0 2 S n0 2.
(e) Moisten a quill or other animal organic matterwith cone. H N O, What color is imparted to it ? Willammonia remove the stain ? Will water wash it out ?
H YDROCH LO R IC AC I D .
36. (a) Put into a 300 cc . flask 20 g . Of common salt,
insert a funnel or thistle tube,which must reach nearly
to the bottom Of the flask,and connect the flask with
three bottles,A
,B
,and C
,B and C being half-full Of
water. Mark w ith a label the level Of the water in B .
GEN ERAL C H EM I S TRY . 29
Pour 40 cc . of cone. H.,SO4 in the flask, and warm gently .
Why do bubbles at fir st pass up through the water in Band C
,and afterward dO not appear in C ? D isconnect
A,connecting the generating flask with B .
Test the gas in A by ( 1) holding near its mouth adrop Of cone. ammonia suspended on the end Of a glassrod
, (2) inserting into the bottle a lighted splint-er, (3)closing the mouth Of the bottle and invert ing it in water.
(0) Notice the level Of the water in B . Test a portionOf the solution in B by adding a few drops Of silver nitrate . Is the white precipitate thus formed soluble inH N O, ?
(d) The reaction in mak ing H C I is N aC l H ZS O,
NaH S O H C I,or at a higher temperature 2N aC l
H,SO, N azS O, ZH OI. In which Of these reactionsis the H zS O, more economically used ? Both reactionsoccur in making the H C Ion a large scale .
Instead Of using a funnel tube in the flask in the aboveexperiment
,the bottles B and C may each be provided
with a third tube Open at both ends,passing through the
stopper and reaching below the surface Of the liquid inthe bottle .
AQ UA REG IA , O R N ITRO - HYDRO C H LO R I C AC I D .
37 Mix 2 cc . Of cone. HNO3 with 6 cc . of H C I. Thismixture is called aqua regia . It dissolves gold . It is
also an excellent solvent for many other metals . Thesolution contains the chloride of the metal .
C ARBO N D IO X I DE .
38 . Pour a little H C I into a test-tube containing asmall quantity Qf sodium carbonate . Apply a lightedSplinter to the mouth of the tube . Suspend in the tubea drop Of clear lime-water on the end Of a glass rod.
30 EXPERIMEN T S .
The gas given eff is carbon dioxide . N a,C O,ZH OI
2N aC l H ,O CO, Would the same gas be evolvedif other carbonates were used ? other acids Try someOf them .
Put 20g . Ofmarble ( C aC O,) in small pieces into a flask .
Cover it with H C I. Collect the gas by downward displacement .
(a) Balance two beakers on a scale, and pour into oneOf them CO , from a bottle or beaker.
Pour CO , from one beaker into another in whicha wax taper is burning ; into a beaker containing limewater . What is formed when CO , is
‘
conducted intolime-water . Try the effect Of H C I on this precipitate .
(c) Breathe through a glass tube into a beaker containing diluted lime-water . If the lime-water becomescloudy
,see if you can make it clear by continuing to
pass into it air from the lungs . What does this experimcnt prove ?
(d) Conduct C O, ,passed through a little water to wash
it,into 5 cc . Of blue litmus solution in a test-tube until
the color Of the solution is changed . N ew warm the litmus solution
,and Observe the change Of color . What
does this experiment prove ? State some Of the properties Of carbon dioxide gas . What is the test for a carbonate ?
PA R T II .
EXPERIM ENTS IN QUALITATIVE ANALY S IS .
T H E M E TA L S .
SEPARAT IO N O F T H E M ETALS I N TO G RO U PS .
39 . Label twenty-four test-tubes as follows : Ag,Al
As’,Ba
,Bi
,Ca
,Cd
,C O
,Cr
,Cu
,Fe
,Hg’
,Hg ”
,K
,Mg
Mn,Na
, (N H 4) , Ni , Pb , Sb , Sn , Sr, and Zn . Place thetubes in a rack
,and pour into eachr
of them 5 cc . Of a S Olution Of a salt Of a metal marked on the label .
(a) Add two or three drops Of H C I to the liquid ineach tube . If a precipitate forms
,determine whether it
is soluble in a larger quantity Of the acid . Group I . in
cludes these metals which form chlorides insoluble inH C I. Which are they ?
(6) Pour into each one Of the tubes wh ich contains asalt Of a metal not belonging to Group I . 5 cc . Of H ,S S O
lutien . Add a larger quantity Of the H ,S in cases inwhich there is an indication that a precipitate is forming .
Group II . includes all these metals (exclusive ofGroup I .) which are precipitated as sulphides in thepresence Of free acid . Which are they Are the members Of Group I . precip itated by H ,S in presence Of freeacid
(c) TO the remaining-
solutions add N H ,OH to neutralize the free acid (What salt Of ammonia is formed ?What does the N H ,OH form with the H ,S in solution
32 EXPERIMEN T S I N
and then a few drops Of yellow ammonium sulphide,
If a precipitate forms, add moreGroup III . includes these metals which are not precipitated by H ,S in the presence Of d ilute acids, but byH ,S in alkaline solutions, or in -neutral or al
kaline solutions . Wh ich metals belong to this group ?Are there any members of Groups I . and II . precipitatedby H ,S in alkaline solutions, or in neutral oralkaline solutions ?
(d) TO the remaining solutions add ammonium carbonate solution . If any Of the carbonatesthus precip itated are soluble in N H ,C l , do not includethem in Group IV . Group IV . includes these metals
( exclusive Of Groups I.,II .
,and III .) which form with
carbonates insoluble in water or in N ILC h ?Name them . Must the solution towhich theis applied for the separation Of Group IV . have an acidor an alkaline reaction ? Add to an acidified
solution Of a salt of Group IV . Does (N precipitate members of Groups I.
,II .
,and III . ?
(6) Add sodium phosphate to the remaining solutions. Group V . is thus separated . What doesthis group include ? Does N a,H PO4 precipitate membersOf Groups I.
,II .
,III .
,and IV . ?
(f ) Group VI . embraces the metals still remaining In
solution . Which are they ?Make out a table for the separation Of a mixture Of S O
lutions Of salts of the above metals into groups .The student should now be required to determ ine
what groups are represented in a mixture given to him .
A group must be completely removed before the test forthe following group is applied H ow can it be determined that the group is completely removed ? Boilinggenerally fac ilitates the formation and separation of a
34 EXPERIMEN T S IN
H ow can a mercurous be distinguished from a mercurie salt ? an iodide from a chromate ?The student should now be given exercises In the de
tection and separation Of the elements in Group I .
G R O U P II .
HYDRO GE N SU LPH I DE GRO UP .
41 . This group is d ivided into Sub-group A,metals
whose sulph ides are soluble in and Sub-groupB
,metals whose sulphides are insoluble (or nearly so) in
Determine by experiment which metals belong tO A . The precipitated sulphides Of Group II . havegenerally the following composition : S b,S 3, As,S , , Bi,S , ,
C dS,C uS
,PbS
,H gS , S nS (brown) , and S nS , (yellow) .
S U B -GROUP A .
S u l ph id es S ol ubl e in Ammon ium S u l ph id e .
(a) Compare the solubility Of Sn, Sb, As , S nO,,S h,O, ,
AS ,O, , S nS , S b,S , , and AS ,S , in boiling cone. H C I; in'
boiling cone. H N O, Record the results in tabular form .
(The sulph ides for th is experiment may be gotten byprecipitating stannous chloride antimoniouschloride and arsenious chloride (AS CI,) withH ,S , and washing the precip itate .) The best solvent for
the metals is nitrO-hydrochloric acid (41 a) , or cone. H C I
tO which a crystal Of KOIO3 is added, form ing stannicchloride S bC l, , and arsenic acid (H aAs0 4) .
(b) Compare the solub ility Of S nS , S b,S , , and AS ,S 3 inboiling cone.
(0) Put a piece Of platinum foil in a porcelain dish andplace on it a piece Of zinc . Cover the Zn and Pt with asolution Of S nC l , . If the Zn is not acted upon
,acidify
with H C I until H is freely given off. Try a sim ilar ex
QUALITATIVE A N ALY S I S . 35
pcriment using S hC l, instead Of S nC l, . (This experiment
must not be tried with a compound of arsenic, nor in amixt
ure of these elements until any arsenic that may be present has been separated from the mixture .)Touch the platinum foil
,if it be blackened
,with a
drop Of conc . H N O,
'
On the end Of a glass rod ; also touchit at another point with a drop Of cone. H C I.
(d) Add H g”C l , to solutions Of S nC l, , S bC l AS CI,
(40 b) .
(e) Blow a small bulb on the end Of an ignit ion tube10 cm . in length . M ix a small quantity Of a dry compound Of arsenic with S ix times its weight Of a dry mixtture Of equal parts Of N a,C O, and potassium cyanide
(KON ) , place in the bulb , and heat . The bulb shouldnot be more than half-full of the mixture . If a mirrorOf arsenic forms in the upper part Of the tube
,break the
tube and test the solubility of the arsenic in sodium hy
pochlorite (N aOC l) . A mirror Of the Sb is . not solublein this reagent .
(f) Mix a very small quantity Of a compound Of arsenicwith N a,C O3 and KC N ,
and heat on charcoal in the reducing flame Of the blow-pipe . Notice the Odor Of thefumes . Heat in like manner an Sb compound
,and when
a globule is Obtained throw the melted globule from thecharcoal on the floor. Let another globule Of Sb cool
,
and compare its color,solubility
,and malleabili ty with
the corresponding properties Of a globule Of Sn gottenin the same way.
(g) Compare the action Of H ,S on an arsenious and anarsenic compound ; on a stannous and a stannic com
pound .
(h) Make some“Magnesia Mixture by precipitating
M gS O4 solution with a large excess Of N H ,OH ,then add
ing N H ,C I tO the precip itate and solution until the pre
36 EXPERIMEN T S IN
cipitate is dissolved . Add “Magnesia Mixture to se
dium arsenite ; to sodium arsenate ; to sodium phosphate .Add AgN O, to a neutral solution Of sodium arsenite ; tosodium arsenate ; to sodium phosphate . Add ammoniummolybdate solution to a few drOps Of sodium arsenite ; tosodium arsenate ; to sod ium phosphate ; and if, after afew minutes
,no precipitate occurs
,warm . How can ar
senites,arsenates
,and phosphates be distinguished from
each other ?Can the precipitation Of Sn
,Sb
,and As by H ,S be pre
vented by the presence Of strong H C I? Which of thesesulphides most readily dissolves in H C I? (41 b) . MakeOut a scheme for the detection and separation of Sn
,Sb
and As.
An exercise should be given in Sub-group A .
S UB -GROUP B .
S u l ph id es In sol ubl e in Amm on ium S u l ph id es .
(a) Which members Of Sub-group B are precipitatedfrom solutions by H,SO, ? by N H ,OH ? Wh ich sul
phides Of Group II . B are dissolved by boiling withH N O3 ? by boiling with H ,S OJ by KON solution ?Make out the results Of these experiments in tabularform . From the above reactions make out a scheme forthe separation Of the members Of Sub-group B .
(b) D issolve the sulphide which is not soluble in H N O,
in cone. H C I to which a crystal Of KC IO, is added , boi l
Off the chlorine and apply a test already known for the
metal in solution .
(0) Add N H ,OH to a solution Of BiC l, . The precipitate is D issolve this precipitate in as small aquantity Of cone. H C Ias possible . The solution containsb ismuth chloride Dilute w ith water. BismuthOxychloride (BiOC l) is precipitated . D ilute w ith water
QUALITATIVE AN ALYS I S . 37
solutions Of BiC l3 and S bC l, . Is either precipitate S Olu
ble in tartaric acid ? The atmosphere sometimes precipitates stannous oxychlor ide ( S nOC l ) from solutions OfS nC l , On standing . H ow could this be distinguishedfrom the oxy chlorides of Bi and Sb ?
(d) Heat Bi,S 3 on charcoal before the blow-pipe . Testin l ike manner C dS .
(e) Sulphur formed by the decomposition Of H ,S or
may be mistaken for a metallic sulph ide . Itmay be recognized by the tests (28 a) . Add an acid toH ,S . Add an acid tO (N Add H ,S to K,C rO, .
Add H ,S to Fe,C l, . C uS i s slightly soluble in warmbut not in sodium hydrosulphide (N aS H ) ;
but H gS i s somewhat soluble in the latter . Hence inthe absence Of Hg
,N aS H is sometimes used instead Of
for the separation Of the sulph ides Of Sub -groupB from those Of Sub-group A . Sodium hydrosulphide ismade by saturating a solut ion Of N aOH with H ,S
.
An exercise should be given in S ub-group A ; also onein a mixture Of Sub-groups A and B
,or in a m ixture Of
Groups I . and II .
G R O U P III .
AMMO N I UM SU LPH I DE GRO UP.
42. (a) Heat C O, Mn , and N i compounds in the boraxbead . Heat a Mn compound w ith a mixture Of N a,C O,
and N aN O, on platinum foil . Heat a Zn compoundmoistened w ith cobalt nitrate on platinum foil . Heatan Al compound strongly on charcoal
,moisten with a.
solution Of cobalt nitrate and heat again . Try a like ex
periment w ith calcium
(b) Place in test-tubes 5 cc . each Of the nitrates,chlo
rides, or sulphates Of Al, C O, Cr, Fe’
,Fe”
,Mn
,Ni
,Zn .
Add N H ,OH . The hydroxides are formed,Al ,(oH )
38 EXPERIMEN T S IN
N Which are dissolved in excess OfN H ,OH Which are soluble in NH 4C l , and consequently not precipitated in the presence Of a suflicient
_quan
tity Of NH ,C l ? Is Fe(OH ) , at al l soluble in N H ,OH ?
(0) Test FeS O, and Fe,C l6 separately with N H ,OH ,
w ith potassium ferrocyanide and with petassium sulphocyanate (KONS) . Boil FeS O, with a fewdrops Of strong H N O, until the solution changes color ;then test portions Of it with N H ,OH ,
K,FeC y , , KON S .
(d) Add solution Of lead acetate to a solution OfK,C rO, . Add solution OfAgN O3 tO a solution Of K,C rO, .
Mi x C r,(OH )6 (see its formation above) w ith N aN O,
and N a,C O, ; treat the fused mass with water, acidifywith acetic acid
,and test the solution with lead acetate ;
w ith AgN O, . How can a compound insoluble in waterbe tested for Cr ?
(e)°
TO solutions Of nitrate,chloride
,or sulphate Of Al
,
Cr,Fe’ add slowly N aOH . The hydroxides are precip
itated. Which Of these precipitates d issolve in excess Of
N aOH in the cold ? DO any dissolve on boiling ? Areany that dissolve in the cold reprecipitated by boiling ?by adding N H 4C I? H ow can Al
,Cr
,and iron in a m ixt
ure be separated , and the presence Of each be shown ,
the iron being in a ferric condition ? the iron being in aferrous condition ? Try the latter.
(f ) TO nitrates,chlorides
,or sulphates Of C O, Mn , Ni ,
and Zn add The precipitates are C OS , M RS
N iS,and Z nS . Note their color . Which are soluble in
H C I? acetic acid ? nitrO-hydrochloric acid ?
(g) Add N aOH tO solutions Of C O, Mn , Ni , and Zn .
The hydroxides Z n(OH ) ,are formed . Are any Of these precip itates soluble in
N aOH ?
QUALITATIVE A N ALY S I S . 9
(h) TO 5 cc . cobaltous chloride ( C OC l ,) add solution
of KON gradually . The precipitate is cobaltous cyanideOn adding an excess Of KC N the precipi
tate dissolves,and the solution contains the double salt
,
potassium cobalto-cyanide analogous to potassium ferrO-cyanide C O( C N ) 4KON
Add one or two drops Of H C I to the solution
,heat it nearly to the boiling point
,and al low it to
stand for five minutes . Then to a portion Of the solutionadd excess Of H C I to the other portion add N aOH inlarge excess
,warm gently
,and add bromine water .
(2) The same as (h) using nickelous chloride (N iC l,)instead Of C OC l , .
In (h) i f instead Of one or two drops Of H C I the solut ion be neutralized or acidified without heating, the petassium cobalto-cyan ide is decomposed and C O( C N ) , is precipitated . But when only a few drops Of the acid areadded (the KON remaining in excess) and the solutionis heated the free hydrocyanic acid (H ON ) convertsthe C O( C N ) , into cobaltic cyanide whichun ites with KON to form potassium cobalti-cyanide
analogous tO potassium ferri - cyanideKON H C I KC I H C N 2H ON
2C O( C N ) , H, C O,( C N ) 6 6KC N
or K,C O( C N ) 6 is not decom
posed by dilute acids and is not precipitated by warmnwith excess Of N aOH and adding bromine water .
Potassium nickelous-cyanide (K in presenceOf KON is not converted by the action Of H C I into acompound corresponding to potassium cobalto-cyanide
,
but is decomposed, and N i( C N ) , precipitated WhenN aOH in large excess is added to a solution Ofand the mixture i s then warmed gently and brom ine water added
,
’
nick el ic hydroxide (N is precipitated
40 EXPERIME N T S IN
K ,N i(C N )6 13Br 3KOH 7KBr Ni(OH ) ,6BrC N . The precipitate should be tested for N i bymeans Of the sodium metaphosphate bead .
C OS and N iS are converted into C oC l , and N iC l , bydissolving in nitrohydrochloric acid . Before addingKON evaporate the above solution almost to drynessand dissolve in water
,adding a few drops of H O' if
necessary for solution .
Take a m ixture Of COCI, and N iC l , , precipitate with
(N and see if you can prove the presence Of C Oand N i by the above process .Make out a scheme for the separation and detection Of
Al,C O
,Cr
,Fe’
,Fe”
,Mn
,Ni
,and Zn in mixtures .
An exercise should be given in Group III .
PRECAUT IO N S IN T H E SEPARAT IO N O F GRO UPS I
I I . , A N D I I I .
43. Perform the following experiments,and then state
what precautions are necessary in the separation Of themembers Of Group III . from the filtrate Of Group II .
(a) Boil 1 cc . Fe,C l6 with H ,S , and then determinewhether the iron is in a ferrous or a ferric state (42 c) .
(b) Boil a solution Of H ,S ; test the gas coming Off
with a p iece Of paper moistened with lead acetate .
When paper moistened with lead acetate is not blackened by holding it tO the mouth Of the test-tube test thesolution w ith lead acetate (39 c) .
(0) Add N H ,OH to a solution Of M gS O, . Add N H ,C I
to a solution Of M gS O, and then add N H ,OH (39 c) .
G R O U P IV .
AMMO N I UM C ARBO N ATE GRO UP .
44. (a) What colors (10 salts Of Ba , Ca, Sr, and Cu givewhen moistened with H C I and held in the flame on the
end of a platinum wire ?
42 EXPERIMEN T S IN
and nitrates may be made from the precipitated carbonates by dissolving the carbonates in as little H C I or
H N O, as possible , evaporating to dryness, taking up ina little water and evaporating again
(d) Are members Of Group I.
,II .
,and III . precipitated
by N H ,C I, N H ,OH ,and (N Make out a scheme
for the separation and detection Of Ba,Ca
,and Sr in
m ixtures .An exercise should be given on Group IV .
G R O U P V
SO D I UM PHO SPHATE GRO UP .
45 . (a) Heat a magnesium salt on charcoal before theblow-pipe ; moisten with a solution Of and heat
again .
(b) To a solution Of magnesium sulphate (M gS OQaddN H ,C I, NE ,QE ,
and sodium phosphateTry th is test with a very dilute solution of M gS O, .
Rubbing the inside Of the test-tube with a glass rod willfacilitate the separation Of the precipitate . The precipitate is
(0) Add barium hydroxide Ba(OH ) , to a solutionOf M gC l , . The precipitate is magnesium hydroxide
It is somewhat soluble in ammoniumsalts What remains in solution ?
G R O U P V I .
SO LUBLE GRO U P .
46. (a) Test salts Of N H , ,K
,and Na on a platinum
wire in the flame . Examine the flame in each case bylook ing through a piece Of blue glass . Mix the threecompounds and examine in the flame without the glass ;through the glass .
QUAL ITATIVE AN ALYS I S . 43
(b) Are NH , ,K
,and Na salts volatile at a faint r ed
heat ? Heat them on platinum foil .
(0) Rub salts Of NH , ,Na
,and K with caustic lime
moistened with water. Notice the Odor.
(d) Add one or two drops Of platinum chloride
(PtC l ,) to neutral or acid solutions Of NH” Na, and Ksalts on watch-glasses . Examine the precipitates witha microscope .
(e) Add tartaric acid to neutra l solutions Of NH” Na,and K salts ; to alkaline solutions .
(f ) Prove the presence Of NH”K
,and Na in a m ixt
ure Of solutions Of N H ,C l , KC l , and N aC l .
SEPARAT IO N OF GRO UPS IV V AND V I.
47. Take a mixture Of BaC l ,, M gC l , , and KC l . AddN H ,C I, NH,OH,
and Filter. TO filtrateadd a few drops Of H,SO, . NVhat is the slight precipitate Filter. What remains in solution in the filtrate ?Remove ammonium salts from the filtrate by evaporatingand heating to faint redness . D issolve the residue inwater and add excess Of What is the precipitate ? What remains in solution ? Add N H ,OH and
What is the precipitate ? Filter . What isin the filtrate ? Evaporate the filtrate and heat tO redness . For what purpose ? Test the residue in the flame .
D issolve the residue in water,adding a few drops Of H C I
to convert any K,C O, that may have been formed intoKC I. Add PtC l4 tO the solution . Examine the precipitate w ith a microscope .
Make out a scheme for the separation Of Mg,K
,and
Na from Group IV . and for proving their presence .
An exercise should be given with a mixture Of salts OfGroups IV .
,V.
,and VI . An exercise should be given
with a mixture containing any or
,
all of the Groups .
44 EXPERIMEN T S IN
SO M E SPE C IAL C ASES U N DER GRO UP I I I .
Ba,Ca
,Sr may be precipitated in Group III . when
present in the form Of phosphate,silicate
,fluoride
,berate
,
or oxalate . As an example Of this we give calcium phosphate48 . D issolve 5 g . in H C I. Divide the solution into three portions
,a,b,and c. To “
it add N H ,OH
to alkaline reaction . D i ssolve the precipitate in H N O,
and test for H,PO4 with ammonium molybdate . D i luteb with ten volumes Of water. TO a small portion Of thissolution add H ,S O then three volumes Of alcohol . Thissuggests a method for the detection Of Ca
,Ba
,and Sr
when precip itated as phosphates in Group III . Anothermethod is indicated by the following experiment : Almost neutralize c with N aOH add an equal volume Ofsodium acetate
,and then a few drops Of acetic acid .
Now add Fe,C l6 drop by drop as long as a precipitateforms and until the liquid after shaking remains reddish .
Heat tO boiling and filter hot . The precipitate Shouldcontain the H,PO,
as phosphate Of iron the filtrate,the
Ca as C aC l , . Test the precipitate for H 3PO, and the fil
trate for Ca .
T H E A C ID S .
IN O R G A N IC A C ID S .
BAR I UM C H LO R I DE GRO UP .
49 . Add BaC l, to the following acids made neutralwith N H ,OH ,
or to neutral solutions Of soluble salts con
taining these acids,and determine which Of the precip
itates are soluble in H OI: acetic , arsenious, arsenic , benzoic
,boric
,carbonic
,chloric
,chromic
,citric , formic ,
hyposulphurous,hyposulphuric (hydrogen sulphide) ,
hydrobrom ic,hydrochloric
,hydriodic
,hydroferrocyanic ,
QUALITATIVE AN ALY S I S . 45
hydroferricyanic,hydrofluoric
,n itric
,oxalic
,phosphoric
,
sulphurous,sulphuric
,and tartaric .
Of the above acids acet ic,benzoic
,carbonic
,oxalic
,and
tartaric are organic .
S I LVER’
N ITRATE GRO UP .
50. (a) Add a few dr ops Of AgN O, to neutral solution s Of salts Of the acids ment ioned in 49 . Note thecolor Of each precipitate . Which Of the precipitates aresoluble in H N O, ? in N H ,OH ? in excess Of the solutionto which the AgN O3 is added ? Compare the results Of49 and 50 (a) .
(b) Put a crystal Of KC l in a test-tube, add a littleblack oxide Of manganese and then a few dropsOf cone. H,SO, . Heat cautiously . Notice the color ofthe gas that is given Off. Try what effect the gas hasupon the color Of some starch paste placed On the end Ofa glass rod
,or dissolved in water. Test KBr and KI in
the same way as KC l .
(0) Test potassium ferrocyan ide with FeS O4 solution ;with a solution Of Fe,C l, . Test potassium ferricyanidewith FeS O, solution ; with a solution Of Fe,C l, . Add afew drops Of Fe,C l6 tO a solution Of FeS O, ; then addsome N aOH
,and warm . IS the precipitate soluble in
H C I? TO a solution Of potassium cyanide (KON ) addFeS O, , a few drops Of Fe,C l N aOH
,warm ; then add
H C I.
S I L I C IC A C I D
5 1 . Acidulate a solution Of sodium Si licate with H C I,
and evaporate to dryness on the water bath . Treat theresidue with water and H C I
,and again evaporate to dry
ness . Silica ( S iO,) insoluble in H C Ishould remain . Heata particle of S iO, in the sodium metaphosphate bead .
Insoluble silicates can be converted into alkaline s il
46 EXPERIMEN T S IN
icates by fusing w ith four parts Of mixed carbonates Ofpotassium and sodium .
HYDRO FLUO R I C AC I D (H F) .
52. Coat a watch-glass with paraffin . Trace a figurein the paraffin
,cutting the lines down tO the glass . Mix
1 g . C aF, in a lead crucible w ith cone. H ,S O, to form athin '
paste. Cover the crucible with the coated watchglass
,and let it stand for half an hour in a warm place .
Remove the wax from the watch-glass . The figure isetched on the glass
BO R I C A C I D
53. (a) With a solution Of a borate form precipitatesby means Of BaC l ,, C aC l , , AgN O, ,
and lead acetate .
What are these precipitates soluble in ?
(b) M ix some borax in a porcelain dish with cone.
H ,S O, ; cover it with alcohol and ignite . Stir the mixture while it is burning and notice the color imparted tothe flame . Try a similar experiment
,omitting the H,SO, .
Vary the experiment by using boric acid instead Of borax,and omitting the H,SO, . Moisten borax with cone.
H , S O, and heat in the loop of a platinum wire in theoxidizing flame . Let the bead cool ; moisten it withglycerin
,and heat again . What other substances color
the flame green ?
(0) Make a solution Of a borate slightly acid with H C I,dip into it a slip Of turmeric paper
,and dry the paper at
a gentle heat .
SULPHURO US A C I D HYPO SU LPHURO US(TH IO SULP H UR I C ) A C I D
54. TO solutions of sodium sulphite and S O
dium hyposulphite add ( 1) H C I; (2) AgN O3
gradually ; (3) Fe,C l, ; (4) C aC l , .
QUAL ITATIVE AN ALY S IS . '‘
3 J
,
C H LO R I C A C I D
55 . (a) Heat a crystal Of KC lO3 before the blow-pipe
on charcoal .
(b) Mix a very smal l quantity Of KC lO3 with KON ,
and heat on platinum’ foil .
(c) Let fall a few drops Of cone. H ,S O, on a crystal Of
KOIO3in a test-tube . Warm gently . (Caution )
O R G A N I C A C ID S .
TEST OF AN O RGA N I C C O MPO U N D .
56. (a) The blackening Of a substance on heating inan ignition tube usually indicates the presence Of an or
ganie acid . Heat in this way potassium tartrate, potassium c itrate
,sodium acetate .
(b) Blackening without charring may be due to theformation Of a black oxide
,and may take place when no
organic acid is present . Heat in an ignitiontube or On platinum foil .The presence Of certain organic acids prevent or re
tard the p recipitation Of some Of the bases by the groupreagents ; hence it is best in making an analysis to removeor destroy organic acids by combustion as above
,or by
other methods given in works on qualitative analysis,
before applying the group reagents .The organic acids are very numerous . The exper
iments here wi ll be limited to Oxalic,tartaric
,citric
,
mal ic,succinic
,benzoic
,formic
,and acetic acids .
C O N C . H , S O , O N O RGA N I C AC I DS .
57. Pour conc . H ,S O, on small quantities Of salts Ofthe above acids in test-tubes . Observe what takes p lace .
After a few minutes,heat . Oxalic and formic acids are
decomposed as follows : C ,H ,O, H ,O CO , CO
C H ,O, H ,O CO . Carbonic oxide ( C O) burns witha blue flame . Test for it at the mouth Of the test-tube .
O XAL IC , TARTAR I C , C ITR I C , AND MAL I C A C I DS .
58 . TO neutral solutions Of salts Of these acids add
(a) C aC l , . The precip itates are soluble in aceticacid The precipitates dissolve incold KOH andfall again on boiling the solution
(b) L ime-water in considerable quantity ; if no precipitate appears, boil .
(0) L ead acetate . The precip itates are soluble inN ILOH
SU C C I N I C , BE N Z O I C , FO RM I C , AND ACET I C AC I DS .
59 . TO solutions of salts Of these acids add :
(a) Fe,C l, ; boil ; treat the precipitates with NH,OH ;then add cone. H C I in excess .
(b) A'mixture Of alcohol,NH,OH,
and C aC l , .
(0) H gN O, ; boil .
(d) Warm a crystal of sodium acetate with cone.
H ,S O, and an equal volume Of alcohol . Acetic ether isformed . Notice the Odor Of it .
O RGA N I C C O M PO U N DS I N SO LUBLE IN WATER .
To detect an organic acid in a compound insolublein water the
’
compound is first decomposed by boiling
with a solution Of Na,C O, . The organic acid goes intosolution in the form Of a sodium salt .60. Boil calcium oxalate (Obtained by adding ammo
nium oxalate to C aC l ,) w ith Na,C O3 solution . Filter.Neutralize the filtrate with acetic acid
,and test for ex
alic acid with C aC l , . Why is acetic acid used instead OfH C I? H OW is calcium oxalate distinguished from calcium tartrate ? from calcium phosphate ?
TH IS BOOK IS DUE ON TH E LAS T DATE
AN IN IT
W ILL BE AS S ES S ED FO R FAILURE TO RETURN
THI S BOO K O N TH E DATE DUE. TH E PEN ALTY
W ILL I N C REA S E TO 5 0 C EN TS O N TH E FO URTH
DAY A N D TO O N TH E S EVEN TH DAY
OVERDU E.
APR 8 1936
0 3 30 1941
JUN 3 1948
