Report 4 Redox Titration

7/24/2019 Report 4 Redox Titration

1/14

The Equivalent Weight of An Unknown Fe Compound

Prepared by:Rodney PujadaDepartment of ChemistryLos Angeles Trade Technical College400 ashington !l"d# Los Angeles CA$arch %&th# %0&&


2/14

Experiment No 4: The Equivalent Weight of anUnknown Fe Compound

Name: odne! "u#ada$a% "artner: Armin &o''ooghi

() (ntrodu*tion

The purpose of the experiment was to use the permanganate ion, a strong oxidizing

agent, in a titration in order to determine the concentration of a FeSO4solution. Purple

MnO4-ion from a standardized potassium permanganate solution was titrated thrice to

gie clear Mn!"with an anal#te of acidi$ed FeSO4 until all the Fe!"in the solution was

oxidized to Fe%". The color of the MnO4-&Mn!"was used as the indicator for the titration.

' (alanced oxidation-reduction, the molarit#&normalit# of the standards potassium

permanganate, and the olume of potassium permanganate used allowed the

determination of the concentration of the FeSO4.

Equivalent weight

)*uialent weight has the dimensions and units of mass, unli+e atomic weight, whichis dimensionless. )*uialent weights were originall# determined (# experiment, (utinsofar as the# are still used are now deried from molar masses. 'dditionall#, thee*uialent weight of a compound can (e calculated (# diiding the molecular weight

(# the num(er of positie or negatie electrical charges that result from thedissolution of the compound.

Potassium permanganate, KMnO4, is widely used as an oxidizing agent in volumetric analysis. In

acidic solution, permanganate ion undergoes a 5-electron reduction to manganeseII! ion"alancing/0eduction/ 12" " MnO4- " 3e- ------- Mn!" " 42!OOxidation / Fe!" -------------------------- Fe%" " e-

alanced oerall/ / +,-.aq/-0n142.aq/- 3Fe-.aq/25 3Fe6-.aq/-0n-.aq/-

4,1.l/

(() 0aterial

35 m6 uret, !35 m6 )rlenme#er 7as+, (uret clamp, wash

(ottle, funnel, 35 m6 and %55 m6 (ea+er, 85 m6 olumetric

c#linder, stirring rod, and 5.8595 : ;MnO4, and un+nown Fe

compound.

0odne# PuProf/ Manuel 'costa M.S.?a#s of class/ Monda# and @ednesda#Time of class/ >.55 A B/85 pm?ate ?ue / March !8 th,!588


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((() "ro*edure

a) =lean and rinse the (uret with distilled water.%) Precondition the (uret (# rinsing it with the ;MnO4 solution two or three

times, and $ll the (uret with a funnel.*) Fill the (uret with 5.8595 : ;MnO4 to exact measurement.d) 0emoe all gas (u((les in the li*uid column of the (uret.e) 0ead the initial olume of ;MnO4(# recording the position of mar+ that

line up with the meniscus of the li*uid column.f) Weigh 7) gram' of the unknown Fe *ompoundg) Tran'fer the 'olid into 37 m$ Erlenme!er 8a'k) Add

around 37 m$ of di'tilled water plu' a%out 7 m$ of 60,914) 9wirl gentl! for the *r!'tal' to di''olve)

h) Add %etween to 4 m$ of +3 ,6"14into the 'olution;and then 'wirl gentl! to mix the 'olution)

i) Ta+e !35 m6 )rlenme#er 7as+ with the solution to the setup(uret.

i. 0ead the initial olume of the (uret containing ;MnO4, Ci;MnO4.

ii. Open the stopcoc+ of the (uret to delier $rst 3 m6;MnO4solution.

iii. =lose the stopcoc+ when the li*uid leel drops to nearthe position of Cf ;MnO4" 3 m6.

i. 0ead the $nal olume of the (uret, Cf ;MnO4. ThediDerence (etween initial and $nal olumes is theamount of ;MnO4in the 7as+.

#) 0ead and record the top (uretEs meniscus reading, which giesthe $nal olume of ;MnO4solution, Cf ;MnO4 .

k) Place the )rlenme#er 7as+ under the (uret open the stopcoc+slowl# to add the ;MnO4 into the solution.

l) 'dd drop (# drop and wait until the color slowl# fades awa#.m) 0ecord the $nal olume Cf ;MnO4 .when the solution turn to pin+.

(&) %5.5 %3.!Final (uret reading &f ;MnO4m6 %5.5 %3.! 45.5

olume of ;MnO4 consumed

m6 3.4 3.! 4.1olume of ;MnO4 consumed6 5.5534

5.553!

5.5541


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(&)= Cal*ulate the > Equivalent' of ?0n14 redu*ed ./Ta%le No

# Formula/

I of )*ui-g compound J :ormalit# : KColume 6

For un No =:I of )*ui-g ;MnO4 J :ormalit# : K Colume 6I of )*ui-g ;MnO4 J 5.8595 : K 5.5534 6I of )*ui-g ;MnO4 J 5.553991

I of )*ui-g ;MnO4 J5.553991

(&) Cal*ulate the > Equivalent' of Fe oxidi@edalancing/0eduction/ 12" " MnO4- " 3e- ------- Mn!" " 42!OOxidation / Fe!" -------------------------- Fe%" " e-

alanced oerall/ / +,-.aq/-0n142.aq/- 3Fe-.aq/25 3Fe6-.aq/-0n-.aq/-

4,1.l/

Therefore (# the following e*uation/

I of )*ui-g ;MnO4 J I of )*ui-g Fe compound

Ta(le no%

Titration ?ata 0un 8 0un ! 0un %

:ormalit# ;MnO4 (ottle)*ui&6 5.8595 5.8595 5.8595olume of ;MnO4 consumed

6 5.5534 5.553! 5.5541

I of )*ui-g ;MnO45.55539

915.55533

>45.55538

%>


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For 0un :o 8/

(# Ta(le :o%?ata/

I of )*ui-g ;MnO4 J 5.5553991I of )*ui-g Fe compound J 5.5553991

(&)6 Cal*ulate the ma'' of unknown Fe *ompound .g/

)*uialentweight J Molecular @eigth & L

Oxidation / Fe!" -------------------------- Fe%" " e-LJ 8 which is transferred electrons.

)*uialent weight for Fe J 33.143 g&mol

Ta(le :o 4

Titration ?ata 0un 8 0un ! 0un %

I of )*ui-g ;MnO45.55539

915.55533

>45.55538

%>

I of )*ui-g Fe compound5.55539

915.55533

>45.55538

%>

I of e*uialent J mass of compound &)*uialent weight

Mass of Hron J I of e*uialent of Fe K )*uialentweight of Fe

Cal*ulate the weight ofFe

0un 8 0un ! 0un %

I of )*ui-g Fe 5.5553991

5.55533>4

5.55538%>

Molecular @eight of Fe 33.143 33.143 33.143

Mass of Fe g5.5%!!>9

!45.5%859!

8315.5!1>18

BB

Mass Gn+nown Fe compoundg

5.!5!B 5.!8>! 5.8B48

of Fe 83.B 84.4 84.1

'erage of Fe in thecompound

83.5


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(&)4 Cal*ulate the per*ent of (ron in the *ompound)

For 0un :o 8/?ata/ Mass of Fe g J 5.5%!> g

Mass Gn+nown Fe compound gJ 5.!5!B g

of Fe in the compound J Mass of Fe g K855 & Mass Gn+nown Fecompound g

of Fe in the compound J 5.5%!> g K855 & 5.!5!B g

of Fe in the compound J83.B

&) Con*lu'ion':

The percentage of 83 of Hron in the compound sample :o !! (# ta(le:o 4.

In t&is experiment, KMnO4

will 'e used to determine t&e percentage o( )e*+

in anunnown solid sample dissolved in water. &e permanganate oxidation o( )e*+ to)e+ is carried out in an acidic solution to prevent t&e air oxidation o( )e*+.

P&osp&oric acid is added to t&e titration mixture to (orm a colorless complex wit&

t&e normally yellow or orange )e+ ion, w&ic& maredly s&arpens t&e appearance o(t&e endpoint.

The indicator in the titration is the Mn!" ion which is nearl# colorless, theend point in titrations using ;MnO4 can (e ta+en as the $rst pin+ colorthat persists in the solution in excess.

eferen*e':

http/&&we(.centre.edu&shi(a&che8%!6&redox.pdf

http/&&we(.centre.edu&shi(a&che8%!6&redox.pdf

http/&&facult#.ccri.edu&etereza+is&8855!5)xp!53,!5Hron!5'nal#sis!5(#

!50edox!5Titration!5NegtN.pdf
http://web.centre.edu/shiba/che132L/redox.pdfhttp://web.centre.edu/shiba/che132L/redox.pdfhttp://faculty.ccri.edu/eterezakis/1100%20Exp%205,%20Iron%20Analysis%20by%20Redox%20Titration%20_egt_.pdfhttp://faculty.ccri.edu/eterezakis/1100%20Exp%205,%20Iron%20Analysis%20by%20Redox%20Titration%20_egt_.pdfhttp://web.centre.edu/shiba/che132L/redox.pdfhttp://web.centre.edu/shiba/che132L/redox.pdfhttp://faculty.ccri.edu/eterezakis/1100%20Exp%205,%20Iron%20Analysis%20by%20Redox%20Titration%20_egt_.pdfhttp://faculty.ccri.edu/eterezakis/1100%20Exp%205,%20Iron%20Analysis%20by%20Redox%20Titration%20_egt_.pdf


7/14

6a(/ uantitatie Oxidation&0eduction

Titration

'lexander ;az(erou+


8/14

THT6):

uantitative 1xidationBedu*tion Titration

PG0POS):

The purpose of the experiment was to use the permanganate ion, a strong oxidizing

agent, in a titration in order to determine the concentration of a FeSO4solution. Purple

MnO4-ion from a standardized potassium permanganate solution was titrated thrice to

gie clear Mn!"with an anal#te of acidi$ed FeSO4 until all the Fe!"in the solution was

oxidized to Fe%". The color of the MnO4-&Mn!"was used as the indicator for the titration.

' (alanced oxidation-reduction, the molarit#&normalit# of the standards potassium

permanganate, and the olume of potassium permanganate used allowed the

determination of the concentration of the FeSO4.

P0O=)?G0):

8. O(tain a(out 855m6 of potassium permanganate solution .5!5M from thestoc+ (ottle

!. O(tain a(out 35m6 of FeSO4 solution%. O(tain ! (urets. 0inse one with 3m6 of FeSO4, discard rinsings, and $ll it with

FeSO4. 0epeat procedure for potassium permanganate and second (uret4. Place 35m6 of distilled water and add 8 drop of potassium permanganate.

O(sere, this will (e the color standard for titration3. Measure 85.5m6 of FeSO4into 7as+ from (uret. 'dd 3.55m6 of %.5M sulfuric acid

to increase 2" concentration. :ow titrate with potassium permanganate as

titrant, reach the endpoint, read the (uret, and discard the contents of the 7as+>. 0inse 7as+ and repeat titration two more times using the same olume of FeSO4

?'T' OS)0C'THO:S/

/. Potassium permanganate solution J deep purple color, stainso BB.! m6 of standardized .5!5M ta+en totalo no cr#stals isi(le, completel# dissoledo color standard for reaction J pin+&purple, not as strong as permanganate

solution*. FeSO4 solution J #ellow&dirt# gre# mur+# color

o 35.5 m6 of FeSO4 solution of un+nown concentration ta+en. Titrations J solution turns pin+&purple where drop of titrant lands, (ut later goes

(ac+ to mur+# #ellow&gre# coloro 'fter endpoint, solution is pin+&purple

4. ?ata Ta(le 8/ Titration olumes/


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TrialH2SO4

addedFeSO4start FeSO4stop KMnO4start KMnO4stop

& '(0mL &4()*mL %4(*0mL +(&,mL %*(%0mL

% '(&mL %4(*0mL -4('+mL %*(%0mL 4-(*'mL

- 4(+mL -4('+mL 44(*&mL %)(+-mL 4'(&)mL

='6=G6'THO:S/

alancing/

0eduction/ 12"" MnO4- " 3e- 25Mn!" " 42!O

Oxidation / Fe!"- Fe%"" e-

12"" MnO4- " 3e- 25Mn!" " 42!O

3Fe!"- 3Fe%"" 3e-

alanced oerall/ +,-.aq/ -0n142.aq/ - 3Fe-.aq/ 25 3Fe6-.aq/ - 0n-.aq/ -

4,1.l/

:ormalit#/

:um(er of electrons transferred J num(er of e*uialents J 3

)*uialent weight/ %B.85g&mol " 34.B4g&mol " 4K8>.55g&mol&3 J %8.>8g&mol

:ormalit# J 3M J 3 K .5!5M J )=77N

Columes/

Trial 8/

FeSO4/ !4.>5m6 - 84.9>m6 J B.14m6

;MnO4/ !>.!5m6 - B.81m6 J 89.5!m6

Trial !/


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FeSO4/ %4.3Bm6 - !4.>5m6 J B.BBm6

;MnO4/ 4%.>3m6 - !>.!5m6 J 89.43m6

Trial %/

FeSO4/ 44.>8m6 - %4.3Bm6 J 85.5!m6

;MnO4/ 43.89m6 - !9.B%m6 J 89.!4m6

'erage/

FeSO4/ B.14m6 " B.BBm6 " 85.5!m6&% J B.B3m6

;MnO4/ 89.5!m6 " 89.43m6 " 89.!4m6&% J 89.!%m6

FeSO4normalit# and molarit#/

89.5!m6 m6 ;MnO4 K 5.855 e*uialents&8555m6 ;MnO4 J 8.95 K 85-% e*uialents

;MnO4

8 e*uialent FeSO4 J 8 e*uialent ;MnO4

8.95 K 85-% e*uialents ;MnO4 J 8.95 K 85-% e*uialents FeSO4

8.95 K 85-% e*uialents FeSO4 & B.14m6 K 8555m6&86 J 7)=6N

:um(er of electrons transferred J num(er of e*uialents J 8, normalit# J molarit#

Molarit# FeSO4J 7)=60

89.43m6 ;MnO4 K 5.855 e*uialents&8555m6 ;MnO4 J 8.93 K 85-% e*uialents ;MnO4


8.93 K 85-% e*uialents ;MnO4 J 8.93 K 85-% e*uialents FeSO4

8.93 K 85-% e*uialents FeSO4 & B.BBm6 K 8555m6&86 J 7)=3N


89.!4m6 ;MnO4 K 5.855 e*uialents&8555m6 ;MnO4 J 8.9! K 85-% e*uialents ;MnO4


8.9! K 85-% e*uialents ;MnO4 J 8.9! K 85-% e*uialents FeSO4


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8.9! K 85-% e*uialents FeSO4 & 85.5!m6 K 8555m6&86 J 7)=N


'erage molarit#/ 5.89%M " 5.893M " 5.89!M&% J 7)=60

=O:=6GSHO:/

The purpose of the la(orator# exercise was to perform an oxidation&reducation

titration (etween a standardized solution of potassium permanganate and an un+nown

iron HH sulfate solution in order to determine the concentration of the latter. The

permanganate ion in the titrant was reduced to Mn!" and the Fe!"in the anal#te was

oxidized to Fe%". )er#thing was done in a solution acidi$ed (# sulfuric acid so that the

MnO4-would get reduced to Mn!"and the extra ox#gen atoms could form water. From

the titration data and the (alanced oxidation&reduction e*uation the normalit# and

molarit# of the FeSO4solution were gotten.

The oxidation&reduction titration was the ma


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a pale mur+# #ellow&gre# color. 's the MnO4- was added to the anal#te, the area

around the drop turned (ecame a pin+&purple color. The titration proceeded until the

entire solution sta#ed purple pin+. Hnitiall#, the purple MnO4-added to the anal#te was

*uic+l# reduced to clear Mn!"and lost its color. 2oweer, after all the Fe!" was oxidized

to Fe%" there was no more reducing agent and thus the MnO4- sta#ed as MnO4-in the

anal#te solution. The addition of extra MnO4-after all the Fe!"has (een oxidized made

the color of the solution a light purple&pin+ color as there was no longer an#thing to

conert the MnO4- to the mostl# colorless slightl# pin+ Mn!". Thus, the potassium

permanganate was the indicator in the reaction. Ht turned clear to Mn!"while there still

was Fe

!"

to oxidize, (ut as excess permanganate was added, the solution turned

purple with MnO4- haing a distinctl# diDerent color. The color standard for the reaction

was simulated (# the addition of a drop of potassium permanganate to water to show

what the potassium permanganate would loo+ li+e after (eing added at the

e*uialence point of the titration. Other oxidizing agents could hae (een used in the

titration as well. For instance, =r!O9!-would hae li+ewise oxidized the Fe!"and could

hae also acted as a self-indicator (ecause of how it also changes color as it goes to

=r%". 6i+ewise, =rO4!-could hae (een used and would hae also changed color as it

oxidized the Fe%". Ox#gen gas noticea(l# reacted with the FeSO4solutions to oxidize

the Fe!"ions. @ith a proper set-up that controlled exactl# how much ox#gen was put

in, it would (e possi(le to use ox#gen gas as an oxidizing agent. Finall#, 2 !O! in an

acidic solution could hae (een used as an oxidizing agent and gien water. # doing

the entire reaction in h#drogen peroxide and seeing how much water was made,

another experiment could hae (een possi(le. 'n#thing with a reduction potential

greater than that of Fe%" " e- - Fe!"could hae (een used as an oxidizing agent.

2oweer, the colorful changes that accompan# the changes of oxidation num(ers of


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manganese and the ease of o(taining manganese-containing compounds made it the

simplest choice.

2aing gotten the olumes necessar# for the titration, the next step calculated

the molarit# of the FeSO4 solution. From the (alanced chemical e*uation, the num(er

of the electrons reacting with MnO4-, and the molarit# of the standardized ;MnO4

solution, the normalit# of the solution was calculated to (e 8.55:. For eer# mole of

MnO4-reduced to Mn!", 3 moles of electrons were re*uired and thus the normalit# of

the solution, 8.55:, was 3 times its molarit#, 5.5!5M. 2oweer, onl# a single mole of

electrons was gotten from the oxidation of Fe!" to Fe%". Thus, there was a 3/8

stoichometric ratio (etween the two reagents. From the normalit# of ;MnO4-and the

olumes used in the titrations, the aerage normalit# of the FeSO4solution was gotten

to (e 5.89%:. That was also e*ual to the molarit# of the solution as the oxidation of

Fe!" to Fe%"dealt with onl# a single electron.

Oerall, it is unli+el# that error pla#ed a ma


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(ut the spontaneous reaction of the solution with air made it appear lower than it

reall# was. This can (e aoided (# performing the reaction in a acuum.

Report 4 Redox Titration

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