IA on effect of bleach temperature on the rate of decolorization of blue dye, measured using visible spectrophotometer.

1. Brilliant blue dye structure. Break down of double bond causes color change
Effect of bleach temp on the rate of decolorization of blue dye, measured using visible spectrophotometer.
Conc bleach - 50 %.
Temp range – RT (24C), 40C, 45, 53C, 57C.
Change of Abs over time – rate of decolorization.
1% blue dye, prepared by dissolving 1ml in 100 ml of DI water (1%v/v)
Rate of decolorization measured using visible spec.
Ea can be calculated.
(Bleach) OCI-
+ Blue dye → colorless product
Reaction mechanism
Procedure:
Bleach conc of 50%.- 50 ml bleach with 50ml water (v/v%)
1% blue dye (1ml dye in 100 ml water).
Blue dye and bleach were incubated at respective temp for 5 mins.
1ml dye added to cuvette. 0.5ml bleach was added, mix and abs over time taken.
Rate of decolorization – change abs over time.
Blue dye and bleach in water bath
1. Comparing chlorine bleach and non chlorine bleach in their ability to remove dye
2. Non chlorine bleach like peroxides, perborates can be investigated
3. Reducing agent bleach like SO2 can be investigated and compared with chlorine bleach
4. UV light source can be used to break double bond, and thus be used in color removal
5. Comparing H2O2 with chlorine bleach in terms of rate of decolorization and Ea study
6. Hypochlorite, OCI- in diff acidic medium, be investigated in their ability for color removal
7. Hypochlorite, OCI- in neutral/basic, be investigated in their ability for color removal
Research Questions

2. Go to expt – press calibrate Insert cuvette (blue dye) and press collect
Insert a blank containing water
Press stop, and click on rainbow icon. Select abs vs time. λ max at 624nm will
be automatically chosen
Abs vs time
Effect of bleach temp on the rate of decolorization of blue dye, measured using visible spectrophotometer.

3. Change of abs over time were plotted.
Rate of decolorization – decrease in abs over time
Slope/gradient taken over 20s
Temp
bleach/C
Rate
Abss-1
24 0.005327
40 0.007201
45 0.008044
53 0.009128
57 0.01367
Data collected.
From data temp at 53C, seems to be an outlier, and was excluded.
Effect of bleach temp on the rate of decolorization of blue dye, measured using visible spectrophotometer.
y = 0.0025e0.0278x
R² = 0.9361
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0 10 20 30 40 50 60
Rate
of
decolorization
temp/C
Temp/C vs Rate of decolorization

4. Arrhenius Eqn
Ea from its gradient
Arrhenius Eqn - Ea by graphical Method
RT
Ea
e
A
k


 .
. 







T
R
E
A
k a 1
ln
ln
Plot ln k vs 1/T
ln both sides
-Ea/R
Gradient = -Ea/R
Gradient = - 2734
-2734 = -Ea/R
Ea = 2734 x 8.314
= 23kJmol-1
ln k
1/T
Temp/K 1/T k ln k
297 3.36 x 10-3 0.005327 -5.234
313 3.19 x 10-3 0.007201 -4.933
318 3.14 x 10-3 0.008044 -4.822
330 3.03 x 10-3 0.01367 -4.292
Arrhenius plot to find Ea.
Assuming rate constant, k. = Rate of decolorization
Ea = 23 k Jmol-1
Lit value Ea.= (55-60 kJmol-1). Most Ea was found to be
in that range, and average 58 was taken.
% error =
(𝐿𝑖𝑡 𝑣𝑎𝑙𝑢𝑒−𝐸𝑥𝑝𝑡 𝑣𝑎𝑙𝑢𝑒)
(𝐿𝑖𝑡 𝑣𝑎𝑙𝑢𝑒)
x100%
% error =
(58 −23)
(58)
x100%=60%
y = -2734.5x + 3.8753
R² = 0.9142
-6
-5
-4
-3
-2
-1
0
0.003 0.00305 0.0031 0.00315 0.0032 0.00325 0.0033 0.00335 0.0034
lnk
1/T
1/T vs lnk
(Bleach) OCI-
+ Blue dye → colorless product

5. Temp and rate constant link by Arrhenius Eqn
X + Y → Z
Rate of rxn = (Total number collision) x ( fraction collision, energy >Ea) x ( [X] [Y] )
Arrhenius Constant
A
Fraction molecule energy > Ea
e –Ea/RT
Conc
[X][Y]
Rate of rxn = A e –Ea/RT [X][Y]
Rate of rxn = k [X] [Y]
If conc constant BUT Temp changes, combine eqn 1 and 2
Rate of rxn = k [X]1
[Y]1
= A e –Ea/RT [X][Y]
k = A e –Ea/RT
Rate rxn written in TWO forms
Rate of rxn = A e –Ea/RT [X] [Y]
Eqn 1 Eqn 2
Cancel both sides
Arrhenius Eqn - Ea by graphical Method
RT
Ea
e
A
k


 .
.








T
R
E
A
k a 1
ln
ln
Plot ln k vs 1/T
• Gradient = -Ea/R
• ln A = intercept y axis
ln both sides
ln k
1/T
-Ea/R
1. Comparing chlorine bleach and non chlorine bleach in their ability to remove dye
2. Non chlorine bleach like peroxides, perborates can be investigated
3. Reducing agent bleach like SO2 can be investigated and compared with chlorine bleach
4. UV light source can be used to break double bond, and thus be used in color removal
5. Comparing H2O2 with chlorine bleach in terms of rate of decolorization and Ea study
6. Hypochlorite, OCI- in diff acidic medium, be investigated in their ability for color removal
7. Hypochlorite, OCI- in neutral/basic, be investigated in their ability for color removal
Research Questions