EX11 Oscillating Chemical Reaction

Topics: Chemistry, Feedback, Oscillation Pages: 5 (1010 words) Published: May 16, 2015
Oscillating chemical reaction
Aim:
The overall reaction rate and concentrations of some reaction intermediates of certain chemical reactions oscillate, even in a homogeneous system. This phenomenon is commonly found in living organisms. These periodical variations occur when a feedback mechanism is available in which a product changes the reaction rate. In this experiment will produce oscillations in both time and space in the concentrations of cerium(IV) and cerium(III) in the BZ reaction. Use the magnetic stirrer bar as experimental techniques and temporal oscillations visualized by Ferroin indicator. this experiment was use the Belousov-Zhabotinskii (BZ) oscillating chemical reaction mechanism briefly discuss the main features of this complex reaction.

Methodology:
Section A – Temporal oscillations visualised by Ferroin indicator Rinse a 100 mL conical flask and a measuring cylinder with deionized water three times as the BV reaction is inhibited by traces of chloride ion. Place a magnetic stirrer bar into the conical flask and add 10 mL of 1.38 M malonic acid solution, 0.312 M potassium bromate solution, 7.5 M sulfuric acid and 3 × 10-3 M Ferroin. Place the flask on a magnetic stirrer plate and switch the stirrer plate on. Leave the stirrer plate on and do not change the stirrer speed for the duration of the experiment. Add the 6ml of 0.05 M (NH4)2Ce(NO3)6 solution and start the electronic timer.

Section B – Temporal oscillations recorded on a computer
Rinse a 100 mL beaker, a 50 mL beaker and a measuring cylinder with deionised water three times. Place a magnetic stirrer bar into the 100 mL beaker and add 10 mL of 1.38 M malonic acid solution, 0.312 M potassium bromate solution and 7.5 M sulfuric acid. Place the beaker on a magnetic stirrer plate and switch the stirrer plate on. Keep the constant speed of stirrer during this experiment. Into the 50 mL beaker add 30 mL of silver nitrate solution. Soak a piece of filter paper in potassium nitrate solution and use this to construct a salt bridge connecting the two beakers. Place a clean strip of silver foil or wire into each beaker and connect leads from the silver electrodes to the computer. Set up the software according to the instructions provided. Finally, add 10 mL of 0.05 M (NH4)2Ce(NO3)6 solution and start the chart recorder.

Section C – Spatial oscillations
Rinse a 100 mL measuring cylinder with deionised water. Into the measuring cylinder add 10 mL of 1.38 M malonic acid solution, 0.312 M potassium bromate solution, 7.5 M sulfuric acid and 3 × 10-3 M Ferroin. Stir until well mixed. Once the solution settles, carefully add 10 mL of 0.05 M (NH4)2Ce(NO3)6 solution down the side of the measuring cylinder using a pipette.

Results:
Section A – Temporal oscillations visualised by Ferroin indicator.

Table1: the induction time and first oscillation time with different volume of Ce(IV) solution (by different groups). volume
induction time (s)
first oscillation time (s)

group1
group 2
group 3
group1
group2
group3
2
1320
2106
2020
9
9
9
4
1100
850
1080
10
8
9
6
136
500

6
14
24
8
484
410

20
21
22
Observation: the solution is blue once the Ferroin is added. About 8:20 min after it has been stirring, the color starts changing from blue to red and purple. The duration of the oscillation (time of color changes blue to red then back to blue) is shown in Diagram 1. The induction time is defined as the time when the color appears to change and in this experiment which is 8:10 min.

Section B – Temporal oscillations recorded on a computer

Zoom in 1~200s

Zoom in 200~400s

Observation: the color of the mix solution varies from yellow, pale yellow to white and repeat those color changes over again. The voltage troughs correspond to dark yellow, and the voltage peaks correspond to pale yellow. At the end the color is pale yellow.

The observation of section C
10ml (NH4)2Ce(NO3)6 with fast speed
There exist...
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