Analysis of Permanganate – Dichromate Mixture

8/18/2019 Analysis of Permanganate – Dichromate Mixture

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Chem126 Lab – Instrumental Analysis

components for ha&ing di%erent properties' most especially on maximum

absorbance di%erence. Since the absorbances are considered additi&e and

must ne&er react with each other in any way as shown in this formula)

A λ1= λ

1 A

1+ λ

1 A

2 (-

A λ2= λ

2 A

1+ λ

2 A

2 (!

where + the measured absorbance and 5 wa&elength

The maximum absorbances of each component should correspond to a

uni6ue wa&elength to pre&ent each resulting absorpti&ity cur&e from

o&erlapping and creating constant and identical results. The permanganate

solution absorbs at a maximum wa&elength around ,2/ nanometers (nm'

while dichromate absorbs at a maximum wa&elength of 72/ nm.

The molar absorpti&ity coe8cient' denoted by ε ' which is the only

constant &alue between measurements' is calculated from the linear

regression function obtained from the graph of concentration &ersus the

absorbance of the substances. Substituting this formula to (- and (! will

pro&ide the concentration of each component)

A=ε Cb (7

where " is the concentration of the sample and b is the path length of the

cu&ette.

The molar absorpti&ity coe8cient that was ta9en from the

standardization process of the permanganate and dichromate solutions is

used to determine the indi&idual absorbances of each component of the

mixture or binary system. The formula is)

A total350=ε350b Mn [ Mn ]+ε

350bCr [Cr ] (4

A total350=ε350b M n [ Mn ]+ε

350bCr [Cr ] (2

where :Mn; and :"r; are the concentrations of each component at the

speci3c wa&elength

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The determination of the concentrations of each component at

di%erent wa&elengths should show a signi3cant di%erence in the two

components' as long their maximum and minimum absorbance refrain from

o&erlapping.

MET-D./0

+ stoc9 solution of about /./- M solution of KMnO 4 was prepared and

standardized* while a solution of -.2 liters of /.!2 M

Separate &olumes of /.2' -./' 7.//' and 4.// milliliter (m= portions were

then pipetted from the standard KMnO4 solution and placed into separate

-// m= &olumetric >as9s. +nother empty >as9 was added to the set and

each >as9 was labeled respecti&ely from - to 2. ?ach solution was then

diluted to mar9 with the /.!2 M solution of

+bout /.22 to /.,/ grams of dried K !"r!O# reagent was weighed on ananalytical balance. This dry reagent was then transferred into a -// m=

&olumetric >as9 and diluted to the mar9 with distilled water. @sing a pipette'

!.//' 4.//' 0.//' and -/.// m= portions of the diluted K !"r!O# were placed

separately into -// m= &olumetric >as9s. +n empty >as9 was added to the

set and the >as9s were numbered from - to 2' respecti&ely. ?ach >as9 was

then diluted to the mar9 with the /.!2 M

The middle permanganate solution' the third one with intermediate

concentration' had its absorbance measured against a blan9 of pure /.!2

minimum reach of the spectrum the inter&als were reduced to e&ery 2 nm.

The absorbance and wa&elengths obtained from each permanganate solution

were plotted in a single graph. The process was repeated for the dichromate

solutions.

Two wa&elengths for the determination of the molar absorpti&ity were

selected from the data. The absorbances of each standard solution were

measured from each wa&elength' and were plotted against the concentration

of each primary ion present in each solution. The molar absorpti&ity was thencalculated from these two wa&elengths.

The absorbances of each standard solution were deri&ed from the

maximum absorption wa&elengths of each. The absorbances were then

plotted against the concentration of each primary ion at the two chosen

wa&elengths. This formed a calibration cur&e where the molar absorpti&ity

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was calculated for each ion. The path length was calculated from the b A

&alues for each wa&elength.

+ 9nown amount of KMnO4 and K !"r!O# solution was prepared in a -//

m= &olumetric >as9. The absorbance was measured for each of the two

pre&iously chosen wa&elengths. The concentration of each of the primaryions present in the solution was then calculated from the absorbances. The

calculated concentrations were then compared with the standard

concentrations obtained from the pre&ious processes.

RE').T' AND DI'()''IN

$eer A =ambertBs law is only &alid for a binary system in a set of

conditions. One of these conditions includes the independence of the

components of the sample analyzed from each other such that they are nonC

interfering* are homogenous* and' the incident radiation must bemonochromatic (D. SanEee&' !/-7. Thus' an instrument cannot di%erentiate

two species present in the sample absorbing speci3c wa&elengths. t can

only determine the total absorbance as shown in e6uations - and !. n this

experiment' an Fun9nownG mixture of K !"r!O# and MnO4 are analyzed by

measuring the absorbances of the solution at two determined wa&elengths.

Hour calibration cur&es were constructed each of which contains the ions

present in the sample.

The wa&elengths which correspond to the highest absorbances of eachstandard solution' K !"r!O# and KMnO4 were determined by the +bsorption

spectrum shown in Higure -. The highest absorbance in the KMnO4 standard

solution corresponds to a wa&elength of 47#.2 nm. The K!"r!O# standard

corresponds to a wa&elength of 2!, nm. These were used to record the

absorbances of the series of standards containing both of the components of

the sample.

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4// 42/ 2// 22/ ,// ,2/ #// #2//

/./2

/.-

/.-2

/.!

/.!2

/.7

/.72

otassium permanganate otassium dichromate

+bsorbance

Ia&elength (nm

&i

gure 1' Absorption Spectrum( )a!elength !s' Absorbance for ma*imum

absorbance determination

Higure ! and 7 shows the calibration cur&es obtained from measuring

the absorbances at 47#.2 nm. Higure ! is the plot of the absorbance against

the concentration of the permanganate ion. Higure 7 is the plot of the

absorbance against the concentration of the dichromate ion. "onse6uently'Higure 4 and 2 are the calibration cur&es obtained from measuring the

absorbances at the 2!, nm of the permanganate and dichromate ion'

respecti&ely. The information needed from these calibration cur&es is the

molar absorpti&ity which is the slope of the calibration cur&es. +ccording to

e6uation 7' if the path length is - cm (such that in this experiment' the

absorbance is linearly related to the concentration with the molar

absorpti&ity as its slope.

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/ 2 -/ -2 !/ !2 7/ 72 4/ 42 2/

/

/./-

/./-

/./!

/./!

/./7

/./7

/./4

/./4

f(x /x J /./-

D -

Asorance 4s" 55m Mn1at 6137"2

55m Mn1

Asorance

&igure 2' Calibration Cur!e( Absorbance !s' ppm $n+ at -./'0

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/ -// !// 7// 4// 2// ,//

/

/.-

/.!

/.7

/.4

/.2

/.,

/.#

/.0

/.L

f(x /x J /

D -

Asorance 4s" 55m (r,7at 6137"2

55m (r,7

Asorance

&igure .' Calibration Cur!e( Absorbance !s' ppm Cr 2+/ at -./'0

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/ 2 -/ -2 !/ !2 7/ 72 4/ 42 2/

/

/.!

/.4

/.,

/.0

-

-.!

f(x /./!x J /./-

D -

Asorance 4s" 55m Mn1at 62,+

55m Mn1

Asorance

&igure 2' Calibration Cur!e( Absorbance !s' ppm $n+ at -026

/ -// !// 7// 4// 2// ,///

/./-

/./!

/./7

/./4

/./2

/./,

f(x /x J /./-

D /.LL

Asorance 4s" 55m (r,7at 62,+

55m (r,7

Asorance

&igure 0' Calibration Cur!e( Absorbance !s' ppm Cr 2+/ at -026

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Table - summarizes the molar +bsorpti&ities in each calibration cur&es.

These were obtained by using the least s6uare methods in determining the

slope of a regression line (Seep +ppendix) "alculations.

Molar +bsorpti&ities (=mgC- cmC- Mn O4

−¿¿437.5

ℇ¿¿

0.000681127

MnO4

−¿¿526

ℇ¿¿

0.020134378

Cr2O72−¿¿437.5

ℇ¿

¿

0.001453089

Cr2O72−¿¿526ℇ¿¿

7.56909×10−5

Table -. Summary of the Molar +bsorpti&ities obtained in each calibration

cur&e.

These molar +bsorpti&ities are used to determine the concentration of

each ion present in the solution. +s mentioned' only the total absorbance in

each speci3c wa&elength can be detected in the instrument. ncorporatingthis concept to e6uation 7 and by measuring the absorbances of the sample

at the two selected wa&elengths' we may be able to get the concentration of

each ion in the sample as shown in e6uations 4 and 2. Manipulating this

system of e6uation' the concentration of the dichromate ion and

permanganate ion can be calculated as follows)

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526

ℇ Mn O4

−¿ ¿¿

Cr2O72−¿¿437.5¿ℇ¿

Mn O4

−¿¿437.5

−¿ℇ¿

Cr2

O7

2−¿¿526¿

ℇ¿¿

b¿ℇ

Mn O4

−¿ ¿526

¿ Mn O

4

−¿¿437.5

− A440¿

ℇ¿

A545¿

[C r2O7 ]=¿

(,

−¿

MnO4

¿

¿

2−¿

Cr2O

7

¿

¿

ℇ MnO4

−¿¿545

¿

Cr2O

7

2−¿¿545¿

ℇ¿

A545−¿

¿

(#

The sample that was analyzed in the experiment consists of 4ml

K !"r!O# and -ml KMnO4. Table ! shows the summary of the concentrations

obtained experimentally and theoretically. The percentage errors in each

determination were calculated. Minimal error resulted in the analysis. This

suggests an accurate laboratory handling and experimentation and also' a

successful experiment.

Ex5erimental Theoretical Percentage Error

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−¿

MnO4

¿ 12.06 ppm 11.88 p pm 1.50

2−¿Cr

2O

7

¿ 227.64 ppm 227.24 ppm 0.18

Table !. Summary of the analysis of the un9nown sample.

(N(.)'IN

Simultaneous determination of the concentration of a sample

composed of two or more components can be done using spectroscopic

measurements. $y using a series of standards of solution present in the

sample' four calibration cur&es were obtained. The slope of these calibration

cur&es were calculated to the molar absorpti&ity. These &alues were used to

calculate for the concentration of the two ions present in the sample. The

sample composed of 4ml K !"r!O# and -ml KMnO4 was analyzed. Thespectroscopic measurements determined the concentration of the

dichromate and permanganate ion to be !!#.,4 ppm and -!., ppm'

respecti&ely. The theoretical &alues for these concentrations were calculated

in order to compare the accuracy of the results of the analysis. + percentage

error of -.2/1 and /.-01 resulted from the determination of the

permanganate and dichromate concentrations. These minimal &alues

indicate accuracy in the analysis and therefore yield no signi3cant di%erence

between the experimental and theoretical &alues.

.ITERAT)RE (ITED


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chemistry.niser.ac.inPlabhandoutsP"!4-C?xp0.pdf. Nate +ccessed)

March -L' !/-,.

?xperiment 0) Simultaneous Spectrophotometric Netermination. Nepartment

of "hemistry' "ollege of Science' Sultan Uaboos @ni&ersity' Sulatanat of

Oman. +pril 7/' !/--. Detrie&ed from)www.eoman.almdares.netPupP772#,P-7/,4/,0-,.doc . Nate +ccessed)

March -L' !/-,.


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1 4#.2-00L!74 /./70 /.L#

able ' Summary of Data using the "otassium $anganese Standards

able 0' Data for the standardi3ation of "otassium $anganese stoc4 solution

"+="@=+TORS

Least S5uares $ethod o determine molar absorpti!ity7

+bsorbance &s. ppm MnO4 at 547#.2 (Hig. !

S xx= Σ x2− ( Σx )

2

n =3704.60529− (100.9776462)

2

4=1155.484031

S xy= Σxy−( ΣxΣy )

❑

n =3.059028695−

[ (100.9776462) (0.09 ) ]❑

4=0.787031654

MnO4

−¿¿437.5

=m=S xy

S xx=

0.787031654

1155.484031=0.000681127

ℇ¿¿

+bsorbance &s. ppm MnO4 at 52!, (Hig. 7

S xx= Σ x2−

( Σx )2

n =3704.60529−

(100.9776462)2

4=1155.484031

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Trial

Initial Volume

=m.>

)se# Volume

=m.>

* 7#.#L /./ 7#.#L

, 7-.-L -./ 7/.-L

3 4!.// --.L/ 7/.-


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❑

n =75.89955079−

[ (100.9776462) (2.085 ) ]4

=23.2649527

MnO4−¿¿526

=m=S xy

S xx= 23.2649527

1155.484031=0.020134378

ℇ¿¿

+bsorbance &s. ppm "r!O# at 547#.2 (Hig. 4

S xx= Σ x2−

( Σx )2

n =593837.2024−

(1363.44 )2

4=129095.044


❑

n =865.89802−[ (1363.44 ) (1.99 ) ]

❑

4 =187.58662

Cr2O

7

2−¿¿437.5

=m=S xy

S xx=

187.58662

129095.044=0.001453089

ℇ¿¿

+bsorbance &s. ppm "r!O# at 52!, (Hig. 2


❑

n =60.2186−

[ (1363.44 ) (0.148) ]❑

4=9.77132

Cr2O

7

2−¿¿526=m=

S xy

S xx=

9.77132

129095.044=7.56909×10

−5

ℇ¿¿

$olarity of KMnO

4

Trial -)0.1264g Na

2C

2O

4

0.03779 L KMn O4×

1mol Na2

C 2

O4

133.96 g Na2 C 2 O4×

2mol KMn O4

5mol Na2 C 2 O4=0.00998746 M KMn O

4

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Trial !)0.1011g Na

2C

2O

4

0.03019 L KMnO 4×

1mol Na2

C 2

O4

133.96g Na2 C 2 O4×

2mol KMn O4

5mol Na2C 2O4=0.009999376 M KMn O

4

Trial 7)

0.1006g Na2

C 2

O4

0.03010 L KMn O4×

1mol Na2

C 2

O4

133.96g Na2 C 2 O4×

2mol KMnO4

5mol Na2C 2O4=0.009979674 M KMn O

4

M KMnO4(average )=

0.00998746 M +0.009999376 M +0.009979674 M 3

=0.009988836 M

Concentration of Standards

ppm Mn O4=

0.009988836mol KMn O4

1 L ×

1mol MnO4

1mol KMn O4×118.93g Mn O

4

1mol MnO4× 1000mg

1g =1187.972309 pp

ppmCr2O

7=

0.5681gK 2Cr

2O

7

0.1 L ×

1000mg

1g =5681 ppmCr

2O

7

"omposition of un9nown using the calibration cur&es

526

ℇ Mn O4

−¿ ¿¿

Cr2O72−¿¿437.5¿ℇ¿

Mn O4−¿

¿437.5−¿ℇ¿

Cr2

O7

2−¿¿526¿

ℇ¿¿

b¿ℇ

Mn O4

−¿ ¿526

¿ Mn O

4

−¿¿437.5

− A440¿

ℇ¿

A545¿

[C r2O7 ]=¿

[Cr2O7 ]= 0.260 (0.00068113)−0.339 (0.020134378 )

(7.56909×10−5 ) (0.00068113)−(0.00145309 ) (0.020134378 )=227.64 ppm

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−¿ Mn O

4

¿

¿2−¿

Cr2

O7

¿

¿

ℇ Mn O4

−¿ ¿545

=0.260−(7.56909×10−5) (227.64 ppm )

0.020134378=12.06 ppm

¿Cr

2O

7

2−¿¿545¿

ℇ¿

A545−¿¿

heoretical composition of un4no8n

[C r2 O7 ]=5681 ppmCr2O7 × 4ml

100ml=227.24 pp m

−¿ Mn O

4

¿

¿¿

"ercentage 9rror

Hor [C r2 O7 ] ' %Error=227.64 ppm−227.24 ppm

227.24 ppm =0.18

Hor

−¿ Mn O

4

¿

¿¿

%Error=12.06 ppm−11.88 pp m

11.88 pp m =1.50

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Analysis of Permanganate – Dichromate Mixture

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