Analytical Chemistry
Physical and Chemical Principles
C. ANALYTICAL CHEMISTRY Analytical Chemistry – branch of chemistry that deals with the separation, identification and composition of o f matter.
Qualitative Analysis (what is present) – type of analysis that reveals reveals the components of the sample sample Quantitative Analysis (how much is present) – type of analysis analysis that determines the the amount of components present present in a sample Methods of Analyses A. Clas Classi sica call Meth Method odss 1. Gravimetric Method – – deals with the measurement of the mass of a substance that is chemically related to the analyte. 2. Volumetric Method – measur measures es the volume volume of soluti solution on neces necessar sary y to react react completely with the analyte. . Mode odern Methods 1. Spectroscopic Method – – measures the electroma!netic radiation produced by the analyte or its interactions with it. 2. Electroanalytic Electroanalytic Method – – measures the electrical properties of the analyte such as current (A), potential ("), resistance ( ), and amount of char!e (coul).
Quantitative Analysis Gravimetric Method of Analysis
Basic Steps on Precipitation Precipitation Method 1. 2. $. '.
#ample #ample is dissol dissolved ved in an appr appropri opriate ate solven solvent. t. A precipitan precipitantt is used used to to convert convert the analyte analyte into into a sparin! sparin!ly ly soluble soluble preci precipitate pitate.. %he precip precipitate itate is convert converted ed into into a product product of &nown composition composition by a suitable suitable heat treatment. %he perce percenta!e nta!e of the the analyte analyte in the the sample sample is calcul calculated ated usin! the !ravimetric !ravimetric factor ()* wt. of precipitate () , analyte in the sample 1++, wt. of sample ()
molar mass of analyte molar mass of precipitate
- analyte y precipitate
Volumetric Methods of Analysis
Standard Solution – Solution – solution of &nown concentration Standardization – Standardization – process of determinin! the concentration of an un&nown solution Primary Standard Standard – – a substance of hi!h purity used for standardiation Characteristics of a Good Primary Standard Standa rd 1. /i!h /i!h pur purit ity y and and hi! hi!h h e0ui e0uiva vale lent nt wei wei!h !htt 2. #table #table toward towardss air air, hi!h hi!h temp tempera eratur turee and and humid humidity ity $. #oluble in in wa water Conditions for a Volumetric Analysis 1. %he react reaction ion must must be rapid and can can be represente represented d by a simple simple balance balanced d e0uation. e0uation. 2. %he reac reactio tion n must must be compl complete ete and no no side side react reaction ion occu occurs. rs. $. An approp appropria riate te indica indicator tor must must be availa available ble in order order to detec detectt the end point point of the the reaction. '
Analytical Chemistry
Physical and Chemical Principles
Types of Titration 1. Direct itration – the analyte reacts with the standard solution directly 2. Bac! itration – an e-cess standard solution is added and the e-cess is determined by the addition of another standard solution $. "eplacement itration – the analyte is converted to a product chemically related to it and the product of such reaction is titrated with a standard solution
Acid–Base Titration Concepts of Acids and Bases LEWIS 4lectron5pair AC3 acceptor 4lectron5pair A#4 donor
BRONSTED-LOWRY
6roton donor 6roton acceptor
ARRHENIS 6roduces 7/$89 in solution 6roduces 77/8 – in solution
7 hydronium ion# protonated $ater or solvated proton 77 hydro%ide ion Strength of Acids and Bases
&onization "eaction – reaction involvin! formation of ions Stron' Acids(Bases – completely ionied in solution /Cl 9 /28 /$89(a0) 9 Cl – (a0) :a8/ 9 /28 :a9(a0) 9 /8 – (a0) )ea! Acids(Bases – partially ionied in solution / 9 /28 ; /$89(a0) 9 – (a0) :/$ 9 /28 ; :/'9(a0) 9 /8 – (a0) Autoprotolysis of )ater /28 9 /28 ; /$89(a0) 9 /8 – (a0) * ) + , % ,- .,/ at 2<C Stron' Acids * /Cl, /r, /, /Cl8', /:8$, /2#8' (only on the first ioniation) Stron' Bases * ases of roup 1A and 2A )ea! Acids * /, /C:, /2#8$, /$68' and or!anic acids )ea! Bases * Ammonia and derivatives Calculation of pH
Stron' Acids * p/ 5 lo! C acid Stron' Bases * p/ 1' lo! n /85 C base )ea! Acids * p/ 5 1 2 lo!
= a Cacid when Cacid =
)ea! Bases * p/ 1' 1 2 lo!
1+++
a
= bC base when C base =
1+++
b
At 2<C> p0 1 p20 + ,/ Hydrolysis of Salts
Acid and base reacts to form salt and water. As a !eneral rule, salts comin! from wea& acids or wea& bases hydrolye in water, that is, only the stron! con?u!ate hydrolyes in water. An acidic salt is formed from the reaction of a stron! acid and wea& base. A 3asic
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Analytical Chemistry
Physical and Chemical Principles
salt results from the reaction of a stron! base and a wea& acid. %hus, a neutral salt is a product of the reaction between a stron! acid and a stron! base. Hydrolysis Reaction of Salts
Acidic #alt * NH!Cl :/
9 '
9
9 /28 ; /$8
= /
9 :/$
= A = :/
$
asic #alt * NaCN –
C:
–
9 /28 ; /8
9 /C: = /
= A = /C:
p0 of Salts
Csalt Csalt 1+++ Acidic #alt * p/ 2 lo! when = / = b 1
Csalt Csalt 1+++ asic #alt * p/ 2 lo! when = / = a 1
Buffer Solutions
#olutions that contains wea& acid or wea& base and its con?u!ate salt. %hese solutions tend to resist chan!es in p0 . p0 of a Buffer Solution
p0 p= a
lo!
acidic componentB basic componentB
f = b is !iven> p/ 1' p= b
lo!
, 0enderson . 0assle3alch E4uation
acidic componentB basic componentB
Primary Standards for Bases 1. enoic Acid, CD/
'G
Analytical Chemistry
Physical and Chemical Principles
chan!es from yellow to blue p= a F .1+
$.
Methyl Eed p/ %ransition Ean!e* '.2 – D.$ chan!es from red to yellow p= a F <.++ Methyl 8ran!e p/ %ransition Ean!e* $.1 – '.' chan!es from oran!e to yellow p= a F $.'D 6henolphthalein p/ %ransition Ean!e* @.$ – 1+.+ chan!es from colorless to pin& p= a F G.++
'.
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Applications of Acid!Base Titration
*5eldahl Method 6Determination of 2r'anic 7itro'en8 #tep 1. 3i!estion %he sample is o-idied in hot, concentrated sulfuric acid, / 2#8' and turns blac&> %o convert . . . Car3on and 0ydro'en to . . . C29 and 0 92 %o convert . . . Amides and Amines to . . . 70 /1 %o convert . . . Azo# Azo%y and 7itro Group to . . . 7 or its o%ide Catalysts Potassium Sulfate 6* 9S2/ 8 – increases the boilin! point of sulfuric acid Mercuric 2%ide 60'28 – increases the rate of reaction Selenious Acid 60 9Se2: 8 – best catalyst #tep 2. 3istillation %he o-idied solution is cooled and then treated with :a8/ to liberate ammonia !as* :/'9 9 /85 :/$(!) 9 /28 lass or porcelain beads are added to avoid bumpin! n some modifications, hydro!en pero-ide is added to decompose or!anic matriformed f mercuric o-ide, 0'2 is used as a catalyst, it is necessary to add sodium thiosulfate, 7a9S 92: to precipitate mercuric sulfide, 0'S . /!29 9 #28$52 9 2/851 /!#(s) 9 #8'52 9 /28 #tep $. %itration #tandard :a8/ solution
1. Hsin! an e-cess amount of /Cl> :/$ 9 /Cl
:/'Cl
%he e-cess /Cl is determined usin! a standard :a8/ solution /Cl 9 :a8/ :aCl 9 /28
:/$
2. Ammonia distilled is collected in a boric acid solution> :/$ 9 /$8$ :/'9 9 /28$52 4-cess /Cl
<+
Analytical Chemistry
Physical and Chemical Principles
%itrate the /$8$ –:/$ solution with standard acid> /28$52 9 /$89 /$8$ 9 /28 Percenta'e Protein in the Sample protein F : 7 f F <.+ (cereals) F D.2< (meat products) F D.$@ (dairy products) Dou3le &ndicator Method 6Mi%ture of Bases8 %he presence of hydro-ide, carbonate and bicarbonate in water is also referred to as al&alinity which is a measure of the acid5neutraliin! capacity of water 8ne method re0uires titration of the mi-ture to reach the phenolphthalein endpoint with the volume recorded as "+56h. 8n the same solution, methyl red is then added and an additional volume is re0uired to reach the end point recorded as "6h5ME Another method re0uires two duplicate samples. 8ne sample is treated with phenolphthalein and the other with methyl red. "olumes of titrant re0uired to reach the phenolphthalein and methyl red endpoints are recorded as "+56h and "+5ME , respectively m5Cresol purple can also be used to detect phenolphthalein al&alinity (6) while bromocresol !reen or methyl oran!e for the total al&alinity (%) Al&alinity relationships Res#l$ %r&m $i$ra$i&n "+56h I "6h5ME "+56h J "6h5ME "+56h F "6h5ME "+56h + K "6h5ME I + "+56h I + K "6h5ME +
NaOH "+56h – "6h5ME + + + "+56h
Na'CO( 2"6h5ME 2"+56h 2"+56h F 2"6h5ME + +
NaHCO( + "6h5ME – "+56h + "6h5ME +
:ote* f analysis involves measurement of volume due to total al&alinity (" +5ME ), use the conversion* "6h5ME F "+5 ME – "+56h
%hese relationships can be summaried usin! the followin! dia!ram*
reci!itation Titration 8ne of the oldest analytical techni0ues that started in the mid–1@++Ls. #ilver nitrate (A!:8$) is commonly employed in such techni0ue. %itration with A!:8$ is often termed as ar'entometric titration. ndicators in Precipitimetry
<1
Analytical Chemistry
Physical and Chemical Principles
%he e0uivalence point can be observed by the followin!*
<2
Analytical Chemistry
Physical and Chemical Principles
a.
formation of a colored secondary precipitate Mohr Method (=.. Mohr, ermany, 1@D<) 3irect method for halides and cyanides %itrant* #ilver nitrate, A!:8 $ %itration Eeaction* A!9 9 Cl –1 A!Cl(s) $hite
ndicator* sodium chromate, :a2Cr8' ndicator Eeaction* 2A!9 9 Cr8'25 A!2Cr8'(s) red
6rimary #tandard for A!:8 $* :aCl %itration is carried out between p/ of –1+. Hsually, a low concentration of chromate is desired to detect the end point clearly since a chromate ion imparts an intense yellow color. b.
formation of a colored comple-ion Volhard Method (acob "olhard, ermany, 1@') 3irect method for silver – ndirect method for halides %itrant* 6otassium thiocyanate, =#C: 3irect %itration Eeaction* A!9 9 #C: –1 A!#C:(s) $hite 9
–1
ndirect %itration Eeactions* A! 9 Cl
A!Cl(s)
e%cess
$hite
9
–1
A! 9 #C:
A!#C:(s) $hite
ndicator* ferric alum ndicator Eeaction* e9$ 9 #C:51 e(#C:)29 red
%itration is carried out in acidic condition to hasten precipitation of ferric ion to its hydrated o-ide form. c.
formation of a colored adsorption comple"a#ans Method (=. a?ans, 6oland, 1@') %itrant* #ilver nitrate, A!:8 $ %itration Eeaction* A!9 9 Cl –1 A!Cl(s) $hite
ndicator* dichlorofluorescein, best for determination of halides and cyanides 4nd point* color chan!e from yellow to pin& %itration is carried out between p/ of '5. 3e-trin is added to prevent e-cessive coa!ulation of the A!Cl precipitate.
Co"!le# $or"ation Titration %his type of titration is used for the determinations of cations. %ypical rea!ents used are or!anic compounds containin! !roups which are electron donors and have the ability to form multiple covalent bonds with the metal ion. $etermination of Cyanide %y the &ie%ig Method %he titration is carried by the dropwise addition of A!:8 $ in a solution of a cyanide formin! a soluble cyanide comple- of silver* 2C: –1 9 A!9 A!(C:)2 –1. %he endpoint of the titration is the formation of a permanent faint turbidity* A!(C:) 2 –1 9 A!9 A! A!(C:)2B(s) $etermination of 'ic(el
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Analytical Chemistry
Physical and Chemical Principles
An ammoniacal solution of nic&el is treated with a measured e-cess of standard cyanide solution and the e-cess is determined by a standard A!:8 $ solution accordin! to the reactions* Addition of 4-cess Cyanide * :i(:/$)D9$ 9 'C: –1 9 D/28 :i(C:)' –1 9 D:/'8/ ac& %itration with A!9 * 2C: –1 9 A!9 A!(C:)2 –1 4ndpoint * A!(C:)2 –1 9 A!9 A!A!(C:)2B(s) Titration )ith *thylenediaminetetraacetic Acid +*$TA, %he structure su!!ests si- potential sites ( he%adentate) for metal bondin!* the four carbo-yl !roups and two amino !roups. Commercially, the free acid and the dehydrate are available. #olutions of 43%A combines with any metal ions in a 1*1 ratio. %he indicator used for titration is the 4riochrome lac& % . or metal ion detections, it is necessary to ad?ust the p/ to or above so that the blue form predominates in the absence of a metal cation. enerally, metal comple-es with 43%A are red as / 2n –1. hen an e-cess 43%A is added, the solution turns blue accordin! to the reaction*
Mn –1 9 /N –$
/n –2 9 MN52
red
blue
$irect Titration )ith Added Metal ons n the determination of Ca 29, small amount of ma!nesium chloride is added to 43%A. nitially, Ca92 displaces M! 92 in the 43%A comple- and the latter combines with 4% producin! a red comple-. hen all the calcium is titrated, the liberated M! 92 is released, combined with the 43%A and the endpoint is observed.
Introduction to Electroc%e"istry An o-idationOreduction reaction is one in which electrons are transferred from one reactant to another. 2%idation reaction involves an increase in the o-idation state of an element while reduction reaction involves a decrease in the o-idation state. Consider the reaction* Ce'9 9 e29 Ce$9 9 e$9 n this reaction, Ce'9 ion or o-idation reaction>LEORA ac0uires an electron from Loss of Electron(s), O-idation, substance o-idied is e29. #uch stron! electron the R educin! A!ent affinity for electrons ma&es '9 or reduction reaction>)EROA Ce an o-idiin! a!ent or an )ain of Electron(s), R eduction, substance reduced is o-idant. 8n the other hand, the O-idiin! A!ent e29 readily !ives its electron and is a reducin! a!ent or reductant. Balancing Redo- Reactions
#tep 1. Assi!n o-idation numbers of each of the species in the reaction Mn8'51 9 :8251 Mn29 9 :8$51 (acidic medium) 9 52
9$ –2
92
9< –2
#tep 2. rite the half–cell reactions. dentify o-idation and reduction reactions. f compounds are present in the reaction, use the ions in the half–cell reaction 8P3A%8:* :8251 :8$51 9 2e 9$
E43HC%8:*
9< 51
Mn8' 9
92
#tep $. alance the reaction by multiplyin! a factor so that the number of electrons on both sides is the same. <'
Analytical Chemistry
Physical and Chemical Principles
8P3A%8: - <*
<:8251 <:8$51 9 1+e 9$
E43HC%8: - 2*
9< 51 '
2Mn8 9 1+e 2Mn92 9
92
<<
Analytical Chemistry
Physical and Chemical Principles
#tep '. alance by addin! /28 to the o-y!en deficient side and /9O8/ 5 on the other side. 8P3A%8: - <* <:8251 9
9< 51 '
2Mn8 9 1D/ 9 1+e 2Mn92 9 @/28
E43HC%8: - 2*
9
9
92
555555555555555555555555555555555555 2Mn8'51 9 <:8251 9 D/9 2Mn92 9 <:8$51 9 $/28 *lectrochemical Cells
Electrochemical cells have two electrodes, which are immersed in an electrolyte solution. #alt brid!es are used to prevent the two solutions from mi-in!. %he cathode in an electrochemical cell is the electrode where reduction occurs. %he anode, on the other hand, is where o%idation occurs. A 'alvanic or voltaic cell is an electrochemical cell that stores electrical ener!y. %he reaction at the anode and the cathode occurs spontaneously and allows flow of electrons from the anode to the cathode with the aid of an e-ternal conductor. n contrast, an electrolytic cell re0uires an e-ternal source of electrical ener!y to operate. Schematic "epresentation of Cells C# * C#'+ ,"'./ ** A0+ ,"'./ * A0 A:83C E4AC%8:
CA%/83C E4AC%8:
Electrode Potentials An electrode potential is the potential of a cell with the hydro!en electrode as the anode. Standard 0ydro'en Electrode 6S0E8 is assi!ned a value of +.+++" at all temperatures. %he standard electrode potential# E of a half reaction is the electrode potential when the activities of all reactants and products are unity (1 M molar concentration and 1 atm partial pressure). Standard "eduction Potential A positive value of the standard reduction potential of an electrode implies that it was used as cathode with the S0E as anode. /i!h positive value of a reduction potential also indicates that the electrode is a 'ood o%idizin' a'ent . hermodynamic Potential of an Electrochemical Cell# E cell %his potential can be computed at standard conditions as follows* 4cell + 4cathode . 4anode Effect of Concentration on Electrode Potentials; 7ernst E4uation
4
At 2<C> 4
4
4
E% n)
ln
CBc 3Bd ... ABa B b ...
+.+
lo!
:ernst 40uation
CBc 3Bd ... ABa B b ...
where* E F !as constant, @.$1' < * mol % F temperature in =elvin n F number of electrons that appear in the half5cell reaction
Analytical Chemistry
Physical and Chemical Principles
F aradayLs constant, GD'@.$@
coul mole e
&#idation–Reduction Titration a. Permanganate Process +.Mn/0 , n acidic medium> Mn8' –1 9 @/9 9
Mn8' –1 9 2/28 9 $e – Mn82 9 '/8 – Standardization of *Mn2/ solution ndicator* self indicatin! Primary Standards 1. A!ainst :a2C28' E-n* C28'52 2C82 9 2e – 2. A!ainst As28$ E-n* As$9 9 '/28 /$As8' 9
T%e A'sor!tion o( Radiation) *ltraviolet and +isi'le f a beam of li!ht passes throu!h a !lass container filled with li0uid, the emer!ent radiation is always less powerful than that enterin!. f the ener!y absorbed is !reater for some visible wavelen!ths than for others, the emer!ent beam will appear colored.
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Analytical Chemistry
Physical and Chemical Principles
Beer1s &a) %he absorption of radiant ener!y by matter can be described usin! eerLs Qaw. Consider a bloc& of an absorbin! material of concentration, c and thic&ness, %*
b
P
P
o
6o
6
A
d-
ln
dP
P
P
P o
lo!
A lo!
ac
3
+ d%
a3c
P o
3c
P
1
3c
where* F transmittance A F absorbance P F emer!ent radiation = F molar absorptivity P o F enterin! radiation
RE+IE, Q*ESTI&NS AN- R&BLEMS 1.
All of the followin! is used as a hy!roscopic material in desiccators e1cep$
a. Ca#8' 2.
b. M!(Cl8')2
c. 628<
d. /2#8'
Analytical methods classified as micro analysis uses sample mass ran!in! from
a. J 1 m!
b. 151+ m!
c. 1+51++ m!
d. I 1++ m!
$.
Chemical which are tested by the manufacturers showin! the actual percenta!es of impurities and labeled on the containers are called RRRRRRRRRR. a. rea!ent !rade chemicals c. certified rea!ent b. analytical rea!ent d. all of these
'.
hat proportion by wei!ht of :a2C28' (1$') to =/C28'/2C28' ([email protected]) that must be mi-ed in a solution so that the normality of the resultin! solution as a reducin! a!ent is three times the normality as an acidS a. +.$$ b. +.D< c. 1.<' d. $.+
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6latinum crucibles can be used for the followin! processes without si!nificant loss e1cep$ a. usion with sodium carbonate, bora- or al&ali bifluorides b. 4vaporation with hydrofluoric acid c. !nition of o-ides of Ca and #r d. /eatin! with sulfides
D.
hat volume of water must be added to concentrated /Cl solution to prepare 1++ mQ +.G<< M /Cl solutionS a. .G mQ b. 1<.@ mQ c. 'D.+ mQ d. G2.1 mQ
<@
Analytical Chemistry
Physical and Chemical Principles
.
hat !rade of water as defined by the ritish #tandard $G@ is suitable for the determination of trace 0uantities which can be prepared by the distillation of de5 ionied waterS a. rade 1 b. rade 2 c. rade $ d. rade '
or numbers 2 to 34> A 2+ wtOwt a0ueous solution of :aCl (<@.'<) at 2< C has a density of 1.1'< !5mQ –1. 4-press the amount of solute in this solution as follows* @.
wtOvol a. 1
b. 1G
c.21
d. 2$
molarity (M) a. +.G@
b. 1.GD
c. $.G2
d. <.@@
1+. molality (m) a. $.'2
b. <.1$
c. D.@'
d. @.
G.
11. %he followin! describes colloidal suspensions formed durin! precipitation e1cep$ a. %hese particles are almost invisible to the na&ed eye b. %hey settle readily from a !iven solution c. %hey are not easily filtered d. none of the these 12. A 1.<1D ! sample of a CaC8$ was dissolved in an acidic solution. %he calcium was precipitated as CaC28'/28 (1'D.11) and the i!nited precipitate at 2$+ C was found to wei!h +.@2'G !. hat is the percenta!e of Ca8 (
a. nucleation
b. coa!ulation
c. a!!lomeration
d. peptiation
Analytical Chemistry
Physical and Chemical Principles
1G. hich of the followin! a0ueous solutions of the same concentration will have the lar0es$ p/ value at 2< CS a. :/$ b. =Cl c. :/'Cl d. :a 2+. hich of the followin! solutions at 2< C will have the l&2es$ p/ valueS a. +.1< M :a 2#8' (= A2 of /2#8' F 1.2 1+ –2) b. <.2 1+ –@ M /Cl c. +.+< M :aC: (= A of /C: F D.2 1+ –1+) d. +.+1 M :/'Cl (= A of :/'9 F <.D 1+ –1+) 21. hich of the followin! acid5base pairs will result in the formation of a buffer solution when titration is done before the e0uivalence pointS
a. :a8/ and /Cl b. =8/ – /:8$
c. :/$ – /r d. all of these
22. hat volume of +.1+2< M /Cl must be added to 1<.D' mQ of +.+G
d. 628<
2D. n the standardiation of an acid solution with primary standard sodium carbonate, why is it necessary to boil the solution before completin! the titrationS a. to eliminate the reaction product, carbon dio-ide and carbonic acid b. to destroy the bufferin! action of the resultin! solution due to the presence of carbonic acid and unreacted hydro!en carbonate c. to achieve a sharper endpoint with methyl red indicator due to the lar!e decrease in p/ d. all of the these 2. Calculate the molarity of :a8/ solution if 12.2< mQ was used to titrate +.2D1< !ram of primary standard =/6. a. +.1+'< b. +.1$<' c. +.2<+G d. +.1DG 2@. hat is the best basis for choosin! the ri!ht indicator for a !iven acid – base titration from amon! the followin!S a. type of acid c. p/ at e0uivalence point b. type of base d. molarity of the acid or base 2G. n standardiin! a solution of :a8/ a!ainst 1.'$1 !rams of =/6, the analyst uses $<.<+ mQ of the al&ali and has to run bac& with @.2< mQ of acid (1mQ F 1+.< m! :a8/). hat is the molarity of the :a8/ solutionS a. +.211@ M b. +.2+'' M c. +.@$1 M d. +.2
D+
Analytical Chemistry
Physical and Chemical Principles
$+. n the titration of a wea& acid with a stron! base, which of the followin! is the best indicator to be usedS a. bromocresol !reen c. methyl red b. methyl oran!e d. phenolphthalein $1. A +.2+<<5! sample of calcite (impure CaC8$) is treated with 2.1@ ml of +.+12 : /Cl and the e-cess is found to re0uire <.'' ml of +.+@DG : :a8/ for bac& titration. Calculate the percenta!e purity of calcite in terms of wtOwt CaC8 $ (1++).
a. 1.@
b. $<.D
c. <$.'
d. 1.2
$2. 6rocess of determinin! the nitro!en content of or!anic materials by mi-in! the sample with powdered copper () o-ide and i!nited to a combustion tube !ivin! C82, /28, :2 and small amounts of nitro!en o-ides. a. =?eldahl Method c. in&ler Method b. 3umas Method d. i?Ls Method or numbers 55 to 56> A <++5m! sample of each mi-ture was analyed for its al&aline content usin! +.1+2< M /Cl via double indicator method. Mi-ture 1 2 $ ' < "+56h (mQ) '.2 +.+1 <.12 D.$ <.D$ "+5ME (mQ) 1+.1@ D.1G 1+.2' D.$@ G.+' $$. hich of the followin! mi-tures contains :a/C8$S a. Mi-tures 2 and ' c. Mi-tures $ and ' b. Mi-tures ' and < d. Mi-tures 1 and 2 $'. Calculate the purity of the sample containin! :a/C8 $ only. a. 1.@2 b. <.22 c. 1+.D'
d. 11.1$
$<. hat is the wt :a8/ for the sample containin! a mi-ture of :a8/5:a 2C8$S a. 1.@2 b. <.22 c. 1+.D' d. 11.1$ $D. n the analysis of nitro!en usin! =?eldahl Method, which of the followin! is added to decompose or!anic matrices present in the sampleS
a. /2#8'
b. /!8
c. = 2#8'
d. /282
$. A .2G5!ram sample of meat was analyed for its nitro!en content usin! =?eldahl Method. Hpon di!estion, the ammonia liberated was collected in 2<+ mQ of +.@<< M /$8$. %he resultin! solution was titrated with $.2< mQ of +.$122 M /Cl usin! mi-ed indicator. 3etermine the protein in the sample usin! D.2< as factor for meat products. a. 1$.G@ b. 2.2' c. 1G.DG d. $.1' $@. hich of the followin! is :8% used as primary standard for the standardiation of al&ali solutionsS a. /!8 b. /2C28' c. /#8$ :/2 d. CD/
Analytical Chemistry
Physical and Chemical Principles
'1. A mi-ture of Qir (@D.@'<) and ar 2 (2G.22) wei!hin! @++ m! is treated <+.++ mQ of +.1@G M A!:8$ and the e-cess is found to re0uire @.D mQ of +.$1G M =#C: for bac& titration, usin! ferric alum as indicator. hat is the percenta!e of ar 2 in the sampleS a. D.G< b. $2.+< c. $<.D2 d. D'.$@ '2. n "olhard Method, why is it necessary to carry out titration in acidic solutionS a. %o prevent precipitation of iron as hydrated as hydrated o-ide b. %o prevent formation of A!#C: precipitate c. %o prevent reduction of halide d. %o prevent precipitation of silver as hydrated as hydrated o-ide '$. A <+.2<5!ram alloy of nic&el was dissolved and treated to remove the impurities. ts ammoniacal solution was treated with <+ mQ of +.1+< M =C: and the e-cess cyanide re0uired 2.2< mQ of +.++G2< M A!:8 $. 3etermine :i (<@.DG) in the alloy. a. 2+.@D b. $.DG c. 1+.<$ d. '1.2 ''. A <++5m! sample containin! :aC: re0uired 2$.<+ mQ of +.12<< M A!:8$ to obtain a permanent faint turbidity. 4-press the result of this analysis as C: – . a. 1<.$' b. 2$.+1 c. 1.2< d. $+.D '<. hich of the followin! ions is best titrated with 43%A at minimum p/ less than S a. Ca92 b. #r 92 c. M!92 d. e9$ 'D. An 43%A solution was prepared by dissolvin! the disodium salt in 1Q of water. t was standardied usin! +.<+D$ !ram of primary standard CaC8 $ and consumed 2@.<+ mQ of the solution. %he standard solution was used to determine the hardness of a 2Q sample of mineral water, which re0uired $<.< mQ of the 43%A solution. 4-press the analysis in terms of ppm CaC8 $. a. @G ppm b. $1D ppm c. 1<@ ppm d. 2DG ppm '. hich of the followin! statements is $r#eS a. Multidentate chelatin! a!ents form wea&er comple-es with metal ions b. All metals can be determined with hi!h precision and accuracy usin! chelometric titration c. 4riochrome blac& % !ives a sharp endpoint for the titration of calcium d. Ca543%A comple- is more stable than M!543%A comple'@. %he $++ m! sample of impure :a2#8' (1'2.+') was dissolved in sufficient water and the sulfate was precipitated by the addition of $<.++ mQ of +.1+22 M aCl2. %he precipitate was removed by filtration and the remainin! aCl 2 consumed D.G mQ of +.2'D M 43%A for titration to the Calma!ite endpoint. Calculate the purity of the sample. a. @+ b. @< c. G+ d. G< 'G. Commonly, the analyte in a sample is present in two different o-idation states. 6re5 reduction is then necessary before titration. 8ne of the metallic reductors is inc soa&ed in a dilute solution of mercuric chloride. %his reductor is &nown as RRRRRRRRRR. a. alden reductor c. Qindlars catalyst b. 3evarda Alloy d. ones reductor
D2
Analytical Chemistry
Physical and Chemical Principles
<+. At p/ F and a pressure of 1 bar, the potential for the half reaction, 2/ 9(a0) 9 2e – /2 (!) is RRRRRRRRRR. a. + " b. –+.'1' " c. –+.@2@ " d. –1.2<< " <1. hich of the followin! is %alse about iodine as an o-idiin! a!ent in titrationS a. #tandard iodine solutions have low smaller electrode potential b. #ensitive and reversible indicators are readily available c. odine is very soluble in water and losses are minimal d. %he solution lac&s stability and re0uires re!ular standardiation <2. hat is the molarity of a =Mn8' solution standardied a!ainst 1.$
d. odide
<'. A sample of iron ore wei!hin! $@<.D m! was dissolved in acid and passed throu!h a ones reductor. %he resultin! solution <2.$D mQ of +.+1'$D M = 2Cr 28 for titration to the diphenylamine sulfonic acid endpoint. Calculate e $8' (2$1.<< !Omol) in the ore sample. a. 1<.+< b. '<.1< c. G+.$+ d. D.G@ <<. A sample of pyrolusite wei!hin! +.2'++ !ram was treated with e-cess =. %he iodine liberated re0uired 'D.2' mQ of +.11+< M :a2#28$ solution. Calculate Mn82 (@D.G') in the sample. a. 'D.2 b. $+.@< c. G2.<' d. D.12
d. "
<. A 1+.++ !ram sample of coo&ed5ham was pureed with 2++ mQ of water, filtered and the resultin! solution containin! dissolved potassium nitrite was acidified. %his solution was treated with 2<.++ mQ of +.++<1' M =Mn8' was bac& titrated with 1'.G mQ of +.+1D@ M e#8'. Calculate the amount of nitrite ('D.+1) in ppm. a. '<+ b. G++ c. 1$<+ d. 1@++ <@. hich of the followin! is used as a pre5o-idantS a. sodium bismuthate b. ammonium pero-ydisulfate
c. sodium pero-ide d. all of these
Molar absorptivity, M –15cm –1B Co :i $D'++ <<2+ 12'+ 1<++
Calculate the concentration of Co in the solution in ppm a. 112 ppm b. 1G'+ ppm c. 21'2 ppm
D$
Absorbance of solution, A +.@1< +.$1' d. 2$'$ ppm
