PART
3
Concepts Related to the Scientific Method
.... _-------_ .. _-----------_..... _----_ ... _-.-----------------------------_._.
INTRODUCTION
I n yo u r work on th e preced ing- pro blems you have learn ed ma ny th ings. For exam pl e.
y O li have d evelo ped an abi lity lO plan ahead . to fo resee di ffic ult ies an d ove rco me them in
advance. Th is is a valu able ability. And , as you learn more chem istr y fro m the problems
in thi s sect ion, th i.. ab ility to plan ahead can be int egrated wit h anothe r skill, proficien cy
in team work. For each assigned problem , arrange an equ itable d ivision of the tasks 1O be
don e with YOU T partner so that eac h of yo u is b usy most o f th e t ime. Pla n YOU T work befo rehand so that while on e par t ner prepares a solu t ion . the ot he r is scn ing u p the apparatu s;
wh ile on e stud ies a refe re nce tex t, t he other carefully reviews the resu lts described in the
laborato ry no tebook s an d then bo th confer, mu t ual ly exchang ing information an d ideas.
Mode rn society is co mplex . T od ay most people work at special tasks, each a mem ber o f a
team : pro ficiency ill tea mwork, learn ed now, will be hel pful later O il.
T he problems listed ill th is secti on d eal p rima ril y with pri nciples that, thus far , yo u
have on ly rea d abo u t. Your instructor lIlay ask yo u , for exa mple , to pre pare a litt le d ecaa nuu inc-s-pcroxod icobalt (I II) terrae lilor -i d c.
O r he lila)' assign YO li the task of pro ving that t he atom ic weigh t of wolfram is
app roxi mate ly 184. Perhaps he will ask you to "how that h ydro gen ch loride can be prepared
by the an ion o f sulfu ric acid on almost an y chloride . You mi gh t be asked to show that nickel
is sta ble in the d ivalent Hate and u nstable in t he tr-ivalen t sta te. Or he m ight assign a pro bleu r from th e list of problems in th is sect ion.
As us ual, you will refer 1O the avai la ble litera ture in the lib rar y and elsewhere. You
will d iseuse th e man cr with yo u r instr uct or an d others. ult imately determi ning a proper
auac k, all the wh ile recording t he necessar y fans and suggestio ns in you r notebook.
O ln .ionsly, 110 lch om tor v u-ork should
that yo u r proposed [noced uve is safe.
Ire
at tempted until
63
Y OUT
instructo r has certified
Prior to perfon niug th e ste ps which you b el ieve will lead to a solu ti on of the problem ,
you will prc pare a written re por t. Th is re port wi ll consist o f th ree par ts:
I. T h e state m ent o f the problem . Copy th e stateme n t from the page.
II. The p roposed method of attack . Descr ibe
III
shor t im pe r ati ve sen ten ces t he step s
to be ta ken.
II I. Demon strat io n of co nsoua ucc. State why your p roposed m ethod will r eall y yield
a solu t ion to you r proble m . Show that the ste ps in you r att ack are pertinen t.
Subm it th is rc port, an d your no te book, to yo u r instructo r. H e wi ll exam ine the report
and , pe rh ap s suggesti ng a few changes, cert ify th at your proposed m eth od is satisfac tory.
T hen carry ou t you r procedure, re cording all impor tant ob serva tions in your no teb ook.
Rewri te, or n eatly correct wh ere n ecessary, you r original r e por t an d add a fourth
sccuon:
I V. The so lu tion of the problem . Show, by citi ng th e res u lts o bt ained in the Iabora .
tory, that th e problem is in deed solve d . If req ui red by th e nature of the problem , include
sam ples of mater ial p repare d in the la bora to ry.
Su b mi t th e ent ire r eport for grad in g. T he gr ade will be deter mined b y co ns iderat ion
of thes e po in ts:
I.
2.
3.
4.
5.
G.
T h e aptness an d efficienc y of the p lan used to ob tain an answer to the p roblem .
Agreemen t o f the res u lts ob tai ne d wit h acce p ted ch emical fact s and principles.
T he m e of go od En gli sh gr am ma r.
T he clarity of your exposit io n.
You r la bora to r y techniq ue .
P ro pe r usc of your labo rator y notebook .
THE PROBLEMS
Group A. A Study of Principle s
l. Sel ect an y ind icator you ch oo se and d etermin e its jJK va lue .
2. P ro ve the valid it y o f Cha rles' law.
3. Pr ove that any salt yo u choose d issolves in wa ter in the form o f io ns.
4 . Show, fo r an y two ele me n ts you choose, that th e law of m u lt ip le proportions is true
for two or more com pou nds of these two clem ents.
5. Show th at m etals below hy d roge n in the electromoti ve ser ies will, u nd er certai n
con d it io ns, d isp lace hyd roge n fro m some acids.
6. Prove Dalto n 's Law of Part ial P r essures.
7. Show th at oxid es o f m etals h ave bas ic properti es and th at oxid es of nonme ta ls ha ve
acid ic properties.
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8. Show tha t, in the series 1\', P, As, Sb . Hi, the metallic character of these el ements
inc reases as atom ic n u mber increases.
9. Show that , because o f h yd ro lysis, a solut ion o f ammoruum sulfide has a lower
concentra tion of sulfide ion than a solution of sod iu m sulfide of the same sto ich iometric
co ncentra t ion .
10. By usin g the Dulong-Petit rel ation and su itable laborator y data , determine th e
approxima te atomic weight of any ele me nt you choose.
Group B. A Study of Principles (continued)
l. Determine the value of R , the gas constant.
2. \ Vhat is the
aceta te per liter?
pH of a solu t ion con taining
I mole of ace tic acid an d 2 mo les of sod iu m
3. Prove the validity of Boyle's law.
1. Show th at , compared wi th each o th er, ti n (II ) su lfide is basic and tin (I V) sul fide
is acid ic.
5. Sho w that the p resence of ammonium aceta te will affect the d egr ee of ionization
of acetic acid, whereas the presence of ammonium ch loride will not affect the degree of
ionizat ion of h ydro chloric acid.
6. Sho w that it is possib le, under proper conditions, for a meta l that is below another
in th e ele ctromot ive series to form ions, wh ile the mo re read ily oxidized metal is precipita ted
fro m so lu tio n.
7. The properties o f an el ement can often be in ferred fro m the beh avior of other
d ements. Demo nstrate, b y labora tor y tests, but witho ut testing every possib ili ty, that it is
reas onable to state tha t all nit rates are solu ble.
8. Sho w that the degree of h ydro lysis of a solu t ion of a salt o f a weak acid an d stro ng
base, selected b y yourself, d epends u pon the temperature of the solutio n.
9. Show that the electron ega ti vity of the ha loge ns, chlor ine th rough iodine, decreases
as the ir atomic n um ber increases.
10. Sho w that, in a solution con tai ning h ydronium and sulfid e ions in equ ilibrium
with hydrogen mo no su lfide ion s and d ihyd rogen sulfide, when the h yd ro n iu m ion co ncentrat ion is increased by a fact or of 10, the sulfid e ion co ncentrat ion is decreased by a factor
o f 100.
Group C. The Proper ties of Substa nces
l. Sho w th at ammon iu m sulfat e hydrolyzes in sol u tion.
2. ' Vha t is the atomic weigh t o f ch lorine ?
3. What is the ion izat ion cons tant of acetic acid?
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4 . W h at is th e equ ival en t weight of tin ?
5. 'Vhat is the valence of alu m in u m?
6. Usi ng dat a ob tained in th e la boratory, p re par e a gra ph sh ow ing th e density of
liqu id wa te r as a func tio n of its tem pe ra ture over the range from 00 C to 100 0 C.
7. ' Vhat ar e th e valence s of ir on?
8. Sh ow that a fused salt will con d uct an electr ic cu rren t.
9. Sh ow that the boi lin g po int of a homologous ser ies of alco h ols is a fu nct ion of their
molecu lar weigh t. N ote: u se on ly a few mill il iters of eac h alcohol.
10. Show that iod id e io n is a reduci ng age nt.
Grou p D. The Properties of Substa nces (continue d)
1. List an y four ox id izing agents in order of decreasing ox id izing po wer an d validate
the list.
2. Show th at potassium d ichromate is an oxi d izing agent.
3. w ha r is th e atom ic weigh t o f magnesium?
4 . Select severa l substanc es and show, by la borato r y tests, that they are all reducing
agents.
5. t vhar is the fJH o f a O. l -Af solution o f acet ic ac id?
6. Show that t he molecu lar weight of oxygen is 32. Caut ion : Do n ot pr e par c element al ox ygen (if yo u d ecide to solve the prob lem in this way) by h eati ng a ch lo rate or
perch lorate.
7. P rove t ha t sod iu m carbona te will react with calcium hydrox ide.
8. By m eans of a su ita b le appara tu s, study the p rope r ties of severa l selecte d me ta ls to
deter m in e wh ich w ill and wh ich wi ll not , nell in the finely div ide d state , react with hot
steam.
9. Show that acetic aci d rea cts more slow ly with l ine than docs h yd roch lori c acid
of the sam e m ol ar ity.
10. Show that the value of any selecte d p hysical pro perty of severa l compou nds
isom er ic to each o ther, wh ich yo u select, de pend s u Jlon th e molecular str uct u re o f the
Isomers .
Group E. Ana lytica l Chem istry, Qualitative Ana lysis
l. Show that acetaldeh yde is an ald ehy de.
2. ' Vha t products arc for m cd in the comb us ti on of the fuel gas used in yo ur
laboratory?
3. ' Vhat is the sm allest con centration of iod ine that can be de tected by the starch te st?
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4. O f wh at is the at mos p here com posed?
5. Show that heel' co n ta ins arsen ic.
6. Show that gel atin e coma ins nitrogen .
7. Show that the ion ,
Cll Br ~ = ,
can exi st in solu t ion.
8. Show th at there is a car bony l group in the acetone molec u le .
9. Se parate an int imat e mixtu re of 5 g of sodi um ch lor ide and 5 g of sucrose.
10. Determ ine t he lean amount of arsenic and of antimony that can be detected h y
the Xla rsh te st.
Group F. Analytical Chemistry, Qualitative Analys is (continued)
As required for ea ch problem , prepare solut ions approximatel y O.03-M in each ion
listed . Deter mi ne, and te st, methods for se par at ing each ion from t he o thers present in
the same solu t ion.
l. AIH +, Ag +, Ba H .
2. H gt H , Cll H , Pb H .
3. Cu ' ", Sn ++++, Fet ".
.1. Sr H,
~ l g H,
Zn H .
5. II g H , Ag", Ca H .
6. BaH, C u H , Ca H , H g H .
7. AI H +, Zn H,
~l gH , ~l n H .
8. II g H , Ca " , Ag -, xs -.
9. Cr, O r- . Fe ++, AP ++. Zn ++.
10. Sn t "t". ClI H , Ag", :\In ++ .
Group G. Analytical Chemistry, Quantitative Analysis
I. As accu r ately as po ssible, dete rmi ne the percen tage of sod iu m ch lorid e
represen tat ive sam p le of t he rock salt in th e bo u le o n th e side she lf.
III
a
2. " ' hat is th e form u la of n ickel su lf ide?
3. \ Vha t is th e per ce n t o f acet ic acid ill vinegar?
4 . \ \' hat is th e value of X in any one , or more, o f t he following or sim ilar for m u las :
C u S O~ ' X Il 1 0 , Z\' a 1 B ~ O .· XH 2 0,
CaSO-l'X H 1 0 ?
5 . Sh ow that the m olecu lar we igh t of am m on ia is a pp ro xim ately I i .
6. Deter m in e th e am ou n t of citric acid as gra ms per 100 m l (you m ay assume that all
the ac id p re '>elll is ci tr ic acid ) in a sample of citr us frui t juice.
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7. Determine th e solubilit y produ ct of an y ..lightl y solu blc salt you choose.
8. Determi ne the mol ar co nce nt ration of amm o nia in the di lute ammonium h ydroxide solu tion o n th e side shel f.
9. \ Vhat is the co mpos it ion of constant-boiling hydroch lori c acid?
10. Determi ne t he first and second ion izat ion constant s of ortho phosphoric acid .
Group H. Anal ytica l Chem istry, Quantitative Ana lysis (continued)
1. Show t hat 13
~
of calcium carbon ate con tai n ap proxima tel y 1.2 g of carbon.
2. Show that th e molecul ar weight of carbon d ioxide is approx imately 44.
3. Pro ve tha t water cons ists of h ydrogen and ox ygcn in th e ra tio of two atoms of
hydrogen to one atom of ox ygen.
4. Determ ine th e percen tage of hydrogen in a su itable piece of sto ne. (N ote: N ot
all kind s of rock conta in hydrogen .)
5. Confirm thc statement, as given o n the label by the man ufact urer, of the per·
ccntage of ni tric acid in a bou le of concent ra ted acid.
6. Det erm ine the value of th e instabil ity consta nt of the complex ion Ag (XH 3)2-.
7. Determine the purity of a sample of bak in g soda . calcu lated as perccntage of ::'\a 2 0 .
8. Prove th at when 100 m l of I -N H CI solut ion are added to 100 m l of I-N i\'aOH
solution, 0.1 eq uiva lent of water is form ed.
9. By a proced ure which re q uire s ti trat ion . de termi ne the carbo n dioxide cont ent
of th e a ir in yo ur lungs as a fu nction of the length of t ime after inh alat ion .
10. \\' ha t is th e purity of the potassium pcrm an ganate in the bou le
011
the side shelf-
Group I. Pre para tions
1. Start in g with re sorcinol and ph thalic an hydri de. prepare a few grams of fluoresce in.
Pro ve th at your prod uct is reasonably pure.
2. Exercising all possible precautions to avoid loss of and contam ina t ion of mater ial .
prc parc pure sod ium chloride from th e rock salt on the side shelf.
3. Convert an y solu ble sulfate to the corres ponding chloride by two d iffere nt me th od v
an d con firm yo ur resu lts.
4. Prepare an aq ueous collo idal d ispersion, free of dissolved elect rol ytes. of ' a ny
chosen water-insoluble su bstance.
5. Purify a few grams of crude borax .
6. Prepare a Iew grams of mon osodium d ihydrogcn orthophospha te and of d isod iurn
mo noh ydrogen ort hopho sphate by mix in g the proper q ua nt it ies of ortho ph ospho t ic acid
and sod ium hydroxide. Prove tha t yo u have pre pared the se salts "
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7. \ Vithout ut ili zing p u re or impure gasco us oxygen, preparc a sample of purc
magnesiu m oxide. Sho w tha t your product is p ure.
8. In the synt hes is of Congo red, whi ch includes a step requiring the diazotizatio n of
bcn zid enc, wha t variab les affect the yield ?
9. Prepare a few grams of zinc chloride , start ing with zin c su lfate. Prove that you
h ave ob ta in ed the desired prod uct.
10. Prepare 10 rnl o f etha nol.
Group J. Preparations (continue d)
l. Prepare 2 g of co ppe r (I) su lfide and 2 g of cop pe r (II) su lfi de .
2. \ Vhat factors affect the yield in the syn thesis of a -prop yl acetate in the laborator y?
3. P repare a small q uant ity, about 0.00 1 mole , of hydroge n b rom ide.
4. P repare a sma ll quan ti ty o f magn esium nitr-ide an d cert ify its pur ity.
5. P rep are a few gra ms of any salt o f a p hospho-oxy acid, salts of orthophosphoric acid
excl u de d , and confi r m yo ur synthesis.
6. P repare a few grams of coarse filamen tous rayon.
i . Prepare a few grams of an y water-soluble wer ner comp lex com po u n d tha t you
choose.
8. P repare I g of iodine.
9. Prepare a few gra ms of an y water-insoluble 'Vern er com plex co m pound t hat you
choose.
10. Prepare 5 g of sod ium h yd rogen su lfa te. P ro ve tha t it is sod ium hyd rogen su lfate.
Group K. Technique
l. At wha t tempera ture is the solu b ility, expressed in grams of salt per lit er of wat er,
of sod iu m ni tra te and potassium n itrate the same?
2. Demo nstrate th at air h as weigh t.
3. Show tha t ni trogen , o btained by th e removal o f oxygen, carbon di oxide, and water
Ya po r from the air, is d ifferent from ni trogen ob tained b y the carefull y co nt rolled react ion
be tween ammoni um ch lori de and sod iu m nitrite. Ca ution : Un less the reaction between
:--: H~CI a nd :'\a:\"0 2 is carefu lly controlled , the nitrogen may be released exp losivel y.
4. Show that the su m of the con d ucti vities of a O.I ·.:\J sod iu m ch lo ride solu tion and
a O. l -M silve r n itra te sol u rion is gre ater tha n the cond uc t ivity o f an equal vol ume o f thes e
two sol ut ions mixed toge ther.
5 . Show, us ing laborato r y data, th at the logari th m o f the yapor pressurc o f an y
sta nce you ch oose is a lin ea r function o f the recip roca l of the abso lu te tcmpera tll r ~
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~
6. Show, for a pai r of su bstances wh ich you cho ose, that whe n a solute is d issolved in
a solvc u r, the volu me o f the solut ion is not equ al to the sum of the volu mes of the separa te
co nsti tucnts.
7. Show t ha t act ivated alu m ina 'will ad sorb a gas.
8. Select any three ind icators whic h change color in the p H ra nge 4 to 9 and de te rmi ne , to the nearest half j )H u nit, t he re lat ion between color o f each ind icato r and the J)l!
o f the solut io n in whic h a few d rops of the indicator so lut ion ha ve been d ispersed.
9. Det ermi ne t he weigh t of a p iece of zin c wit ho ut weig hing it or any o th er su bstance
o n a balance or other weigh ing d evice.
10. Sho w that th e su m o f the cond uctivi t ies of a n.I -At acet ic acid solu tion and a O.l -AI
am mon iu m h ydro x ide solution is less than the co nd uct ivity o f a mi xture of eq ual volu me s
of these two solu tions.
Group L. Techni que (continued)
1. Prepare a few m illiliters of any easily liq uefied gas.
2. From the stand poin t of cur rent cost and from labo ratory data , d ete rmine whic h is
the best, next best, nex t to poores t, an d poorest, antifreeze : sod iu m sulfa te, calciu m chloride,
glycerine, ethyl alcohol.
3. Determ ine th e d ensit y of a large piece of mo ssy tin .
4. Compare the prod ucts formed in the d estruct ive d istilla tion of bitum ino us and of
anthracite coal.
5. Measure the rel at ive h umidi ty o f the ai r in the laboratory.
6. Using a calomel electrode, a plati nu m electr ode, an d a po ten tiom eter, tit rate
O.Ol -Al iron (II ) su lfate solution (in a beake r) with O.OI-At po tassium dichromat e solu tion
(in a b u ret ). Draw a titration cu rve an d determ ine the endpoin t.
7. Using data ob tained by steam di stillation , an d oth er necessary information fro m
reference wor ks, ca lculate the molecular weigh t o f nitrobenzene .
8. Show that the su m of the condu cti vit ies of a I-M h yd rochlori c acid solut ion an d
a I-At sod iu m h ydroxide solut ion is greater than the con d uct ivity of a m ix tu re o f eq ual
volu mes o f these two sol u tions.
9. Show that acti vated charcoal will adsorb a solute from a solu tio n .
10. Show th at acet ic acid is d imeric when d issolved in car bo n tetr achlorid e.
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