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

1. Effect of bleach concentration on the rate of decolorization of blue dye, measured using visible spectrophotometer.
Conc bleach - 60 to 100 % used.
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.
Order can be calculated.
Brilliant blue dye structure. Break down of double bond causes color change
(Bleach) OCI-
+ Blue dye → colorless product
Reaction mechanism
Procedure:
Bleach conc of 60 – 100%. 60% - 60 ml bleach with 40ml water (v/v%)
1% blue dye (1ml dye in 100 ml water).
1ml dye added to cuvette. 0.5ml bleach was added, mix and abs over time taken.
Rate of decolorization – change abs over time.
Visible spec

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 concentration 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 40s
Conc
bleach/%
Rate
Abss-1
60 0.0004363
70 0.001270
80 0.002474
90 0.00302
100 0.003941
Data collected.
Effect of bleach concentration on the rate of decolorization of blue dye, measured using visible spectrophotometer.
y = 2E-11x4.2146
R² = 0.9333
0
0.001
0.002
0.003
0.004
0.005
0.006
0 20 40 60 80 100 120
Rate
conc bleach/%
Rate of decolorization vs conc bleach/%
From the graph – it seems like 4th order, which is highly unlikely.

4. Graphical Representation of Order :ZERO, FIRST and SECOND order
FIRST ORDER SECOND ORDER
Rate – 2nd order respect to [A]
Conc x2 – Rate x 4
Unit for k
Rate = k[A]2
Rate = kA2
k = M-1s-1
Rate
Conc reactant Conc reactant
Conc Conc
Time Time
Rate
Time
ln At
Time
1/At
Rate = k[A]1
Rate - 1st order respect to [A]
Unit for k
Rate = k[A]1
Rate = kA
k = s-1
Rate vs Conc - proportional
Conc vs Time
kt
A
A
e
A
A
o
t
kt
o
t


 
]
ln[
]
ln[
]
[
]
[
kt
A
A o
t


]
[
1
]
[
1
ln Ao
1/Ao
Expt Conc
bleach/%
Rate
Abss-1
1 60 0.0004363
2 70 0.001270
3 80 0.002474
4 90 0.00302
5 100 0.003941
% error =
(2−2.5)
2
x 100%= 25%

5. Order of rxn found using THREE mtds
Initial Rate mtd
(Multiple Single Runs)
Conc Vs Time Mtd
(Half Life)
Conc Vs Time Mtd
(Whole Curve/Tangent)
Multiple Single Runs
Vary/Keep certain conc fixed
Wasteful as multiple runs needed
Monitor decrease in conc reactant
Using Half Life to determine order
Monitor decrease conc of single reactant
Using gradient/ tangent at diff conc
Conc x2 – rate x2 - 1st order
Conc x2 – rate x4 – 2nd order
Conc x2 – rate 0 – zero order Convert Conc Vs Time to Rate vs Conc
Rate Vs Conc – Linear – 1st Order
Initial Rate taken, time 0
Draw tangent at time 0
Half Life directly prop to Conc
Half Life inversely prop to Conc
Expt Conc
A
Conc
B
Initial
rate
1 0.01 0.02 2
2 0.01 0.04 4
3 0.02 0.02 4
Conc
Time
Expt 2
Expt 1
Conc reactant
Time
Zero order
Conc reactant
Time
Half Life constant
1st order
2nd order
Conc reactant
Time
Gradient at diff conc
Conc
Rate

6. Why transition metals ion complexes have diff colour?
Transition Metal – Colour Complexes
Colour you see is BLUE – Blue reflected/transmitted to your eyes
- Red/orange absorbed (complementary colour)
Colour you see is Yellow – Yellow reflected/transmitted to your eyes
- Violet absorbed (complementary colour)
complementary colour
Blue
transmitted
Wave length - absorbed
Wave length - absorbed
Visible
light
Visible
light
Yellow
transmitted
absorbed