Ms thesis presentation final

1. PREPARATION AND CHARACTERIZATION OF
SOLUBLE COLLOIDAL MANGANESE DIOXIDE
AND
KINETICS INVESTIGATION OF ITS REACTION
WITH ACIDS
MD. AMINUL ISLAM
MS EXAMINATION ROLL - 2904
SESSION: 2004 - 05

2. Soluble Colloidal Manganese Dioxide
They are not big enough to make the medium opaque
The colloidal system appears transparent to visible light.
Therefore, the system is regarded as a solution
Colloidal (MnO2)n particles have been suggested to be
intermediates in the reduction of MnO4
- ions by a variety of
reducing agents
(MnO2)n particles with n in the range 50 – 100 dispersed in the
aqueous medium

3. SUMMARY
(1) Colloidal MnO2 : prepared by three methods.
: Characterized by chemical analysis,
spectrophotometric and coagulation methods
(2) Kinetics of the reactions of colloidal MnO2 with
four acids in aqueous solution at 250C

4. Preparation
Method-1:
2MnO4
–
(aq) + 3MnSO4 (aq) + 2H2O (l) = 5MnO2 (aq)
+ 4H+
(aq) + 3SO4
2-
(aq)
Method-2:
8MnO4
–
(aq) + 3S2O3
2-
(aq) + 2H+
(aq) = 8MnO2 (aq) +
H2O (l) + 6SO4
2-(aq)
Method-3:
2MnO4
–
(aq) + 3HCOOH (aq) + 2H+
(aq) = 2MnO2 (aq)
+ 4H2O (l) + 3CO2 (g)

5. Chemical Analysis
The average oxidation state of the Mn - species
was determined by estimating the I2 produced
from KI, and found to be + 4.13
pMnx+ + 2qI- = pMn2+ + qI2
I2 estimated spectrophotometrically as I3
- at 351 nm.
I2 (aq) + I- (aq) ↔ I3
- (aq)

6. Fig.1: Spectra of 1.0×10-4 M KMnO4 (1) and the
reaction product (MnO2) (2) of KMnO4 and
MnSO
Wavelength/nm
200 300 400 500 600 700 800
Absorbance
0.0
0.1
0.2
0.3
0.4
(1)
(2)

7. [MnO2] X1O4 M
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Absorbance
at
390
nm
0.0
0.2
0.4
0.6
0.8
1.0
Fig. 3: Determination of
MnO2
log ()
2.6 2.7 2.8 2.9 3.0
log(A)
-2.0
-1.5
-1.0
-0.5
0.0
Fig.2: log(A)vs. log(λ) plot for
the spectrum (400-800nm) of
the MnO2
A = C λ- 4

8. Wavelength/nm
200 300 400 500 600 700
Absorbance
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
(1)
(2)
(3)
(4)
(7)
(5)
(6)
KINETICS OF THE REACTIONS OF MnO2 WITH FOUR ACIDS IN
AQUEOUS SOLUTION AT 250C
1. Kinetics of the reduction of MnO2 by HCl in aq. solution at 250C
Fig.4: Spectra of successive scanning at the intervals of 1.5 minutes
during the progress of the reaction of 1.010- 4 M MnO2 with 2.5 M

9. Fig. 5: The decay profiles of
MnO2
Time/sec
0 200 400 600 800 1000 1200 1400
Absorbance
at
390
nm
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
(1)
(2)
(3)
(4)
(5)
[HCl]0 = (1) 1.26 M
(2) 2.50 M
(3) 3.14 M
(4) 3.77 M
(5) 5.03 M
Fig.6: Influence of [HCl]0 on
the initial rates of the reaction
[HCl]o/M
0 1 2 3 4 5 6
R
i
x10
8
/mol
L
-1
s
-1
0
1
2
3
4
5
6
7
8

10. ln[HCl]0
0.0 0.5 1.0 1.5 2.0
lnR
i
-18.5
-18.0
-17.5
-17.0
-16.5
-16.0
Fig.7: Determination of
the order with respect to
HCl
ln[MnO2]
-10.9 -10.8 -10.7 -10.6 -10.5 -10.4 -10.3 -10.2 -10.1 -10.0
lnR
-17.2
-17.1
-17.0
-16.9
-16.8
-16.7
-16.6
Fig.8: Determination of the
order with respect to MnO2

11. Fig.9: ln(A0 /A) vs. t
plots for five [HCl]0
Fig.10: A comparison of the decay
profiles of MnO2 with the decay of
the Sav of the Mn-species
Time/s
0 100 200 300 400 500 600 700 800
Average
oxidation
state
1
2
3
4
5
0.00
0.06
0.12
0.18
0.24
0.30
Absorbance
at
351nm
(1)=Average oxidation state of Mn species
(1)
(2)=Decay profiles of MnO2
(2)
Time/sec
0 100 200 300 400 500 600
ln(A
0
/A)
0.0
0.1
0.2
0.3
0.4
(1)
(2)
(3)
(4)
(5)

12. Fig.11 : Decay profiles of
MnO2
2. Kinetics of the reaction of MnO2 with HClO4 in aq. solution at
250C
Time/sec
0 200 400 600 800 1000 1200 1400
Absorbance
at
390
nm
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
[HClO4]0 = (1) 1.33 M
(2) 2.65 M
(3) 3.98 M
(4) 5.30 M
(5) 6.63 M
(1)
(2)
(3)
(4)
(5)
ln[HClO4]0/M
0.0 0.5 1.0 1.5 2.0
lnR
i
-18.4
-18.2
-18.0
-17.8
-17.6
-17.4
-17.2
Fig.12: Determination of the
order with respect to HClO4

13. 3. Kinetics of the reaction of MnO2 with H3PO4 in aq.
solution at 250C
Fig.13: Decay profiles of
MnO2
Time/sec
0 100 200 300 400 500
Absorbance
at
390
nm
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
(1)
(2)
(3)
(4)
(5)
[H3PO4]0= (1) 0.24x10
-2
M
(4) 0.96x10
-2
M
(3) 0.72x10
-2
M
(2) 0.48x10
-2
M
(5) 1.2x10
-2
M
[H3PO4]0/ M
-7.5 -7.0 -6.5 -6.0 -5.5 -5.0 -4.5 -4.0 -3.5
lnR
i
-19.0
-18.5
-18.0
-17.5
-17.0
-16.5
-16.0
-15.5
-15.0
-14.5
-14.0
Fig.14: Determination of
the order with respect to
H3PO4

14. 4.The kinetics of the reduction of MnO2 by HCOOH in
aq. solution at 250C:
Fig.15: Decay profiles of
MnO2
ln[HCOOH]0
-3 -2 -1 0
lnR
i
-18.0
-17.5
-17.0
-16.5
Fig.16: Determination of the
order with respect to HCOOH
Time/sec
0 200 400 600 800 1000 1200 1400
Absorbance
at
390
nm
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
[HCOOH]0 = (1) 0.22 M
(2) 0.44 M
(3) 0.67 M
(4) 0.89 M
(5) 1.11 M
(1)
(2)
(3)
(4)
(5)

15. 1. The λmax and MnO2 depend on the method of preparation of
colloidal MnO2
2. log(A) vs. log(λ) plot gives a straight line with a slope of - 4.2
which is close to the value predicted by Rayleigh’s law for the
presence of colloidal particles
3. Coagulating efficiency depends on the conc. and on the charge
carried by the cation of the electrolytes
4. The decay profiles of MnO2 are exponential in nature. So, the
possibility of autocatalysis is not ruled out
5. The product mixture was transparent indicating that MnO2 was
not coagulated
CONCLUSION

16. CONCLUSION (contd -1)
6. The product mixture became colorless, indicating that the
ultimate product of the reaction was Mn2+ species only
7. The rate of decay of MnO2 decreases with increasing time.
8. The rate of decay of MnO2 increases with increasing acid conc.
9. The order with respect to HCl is 1.12; w r to HClO4 is 0.62; w r
to H3PO4 is 1.2 , w r to HCOOH is 0.51 and w r to MnO2 is 0.62
for 5.03M HCl.
10. ln (A0/A) vs. t plots are linear in case of H3PO4 only.

17. 11. The rate of decay of the Sav from + 4 to + 2 was slower than the
rate of decay of MnO2.This is attributed to secondary reactions
leading to formation of the final product species Mn 2+.
12. The reaction of MnO2 with acid does not follow a simple
reaction scheme. The actual reaction is not only complicated, it
appears to depend on the nature and conc. of acid.
13. A mechanism has been proposed but a quantitative
explanation of the kinetic data on the basis of this mechanism
could not be made.
CONCLUSION (contd - 2 )

18. 1. MnO2 (aq) + 4H+
(aq) → Mn 4+
(aq) + H2O (l)
2. Mn 4+
(aq) + 2Cl-
(aq) → Mn 2+
(aq) + Cl2 (g)
3. MnO2(aq) + HClO4(aq) → Mn4+
(aq) + H2O (l) + other products
4. MnO2(aq) + HClO4(aq) → MnO2 - HClO4
5. MnO2(aq) + H3PO4(aq) → Mn4+
(aq) + H2O(l) + other products
6. MnO2(aq) + H3PO4(aq) → MnO2 - H3PO4
7. Mn4+
(aq) + H3PO4 → Mn (1V) - H3PO4 complex
8. MnO2(aq) + HCOO-
(aq) → [MnO2.HCOO] -
(aq)
9. [MnO2.HCOO]-
(aq) + H+
(aq) → Mn2+
(aq) + CO2 (g)+ 2OH-
(aq)
10. Mn2+
(aq)+ HCOO-
(aq) → [Mn (HCOO)]+
(aq)
14. The following reactions are speculated to occur in the MnO2 –
acid system:
CONCLUSION (contd - 3 )

19. Thank you all