Hydrogen Peroxide Concentration and Iodine Clock Reaction

Categories: Chemistry

Essay, Pages 4 (1000 words)

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Research Question

How does changing the concentration of hydrogen peroxide affect the time taken for the iodine clock reaction to occur?

Rationale

A chemical reaction involves the conversion of reactants into products through the rearrangement of atoms (Treichel, 2019). The rate of a chemical reaction depends on the frequency and energy of particle collisions (Holewa, 2019).

The collision theory explains why reactions occur at different rates and emphasizes the need for effective collisions, which involve proper orientation and sufficient energy (Lawson, 2019). Activation energy is the minimum energy required for a reaction to occur (Gregersen, 2018).

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Factors like temperature, pressure, reactant concentration, and the presence of catalysts can influence reaction rates. Temperature increases kinetic energy and collision frequency (Clark, 2002), while catalysts lower activation energy (Holewa, 2019). Additionally, increasing the surface area of reactants increases collision opportunities.

In this experiment, we investigate how changing the concentration of hydrogen peroxide affects the iodine clock reaction.

Original Experiment

The Iodine Clock Reaction

Combine the following solutions in a 250ml conical flask using pipettes:
- Sulfuric Acid (0.25 mol) - 25ml
- Starch 2% - 3ml
- Distilled Water - 24ml
- Potassium Iodide (0.10 mol) - 1ml
- Sodium Thiosulfate (0.002 mol) - 10ml
Measure 0.10 mol of hydrogen peroxide using a pipette and transfer it to a test tube.
Pour the hydrogen peroxide into the flask, start timing, and mix thoroughly.
Record the time when the blue color of the starch-iodine complex appears.

Modified Experiment

Materials

Pipette x 1
250ml conical flask x 12
Stopwatch x 4
50ml measuring cylinder x 1
Box of labels
Sulfuric Acid (0.25 mol) = 2.5L
Starch 2% = 250mL
Distilled Water = 2L
Potassium Iodide (0.10 mol) = 700mL
Sodium Thiosulfate (0.002 mol) = 250mL
Hydrogen Peroxide (0.10 mol) = 500mL

The Iodine Clock Reaction

Combine the following solutions in a 250ml conical flask using pipettes:

Sulfuric Acid (0.25 mol) - 25ml
Starch 2% - 3ml
Distilled Water - 24ml
Potassium Iodide (0.10 mol) - 2ml
Sodium Thiosulfate (0.002 mol) - 10ml

Measure 5ml of hydrogen peroxide (0.10 mol) using a pipette and transfer it to a test tube.
Pour the hydrogen peroxide into the flask, start timing, and mix thoroughly.
Record the time when the blue color of the starch-iodine complex appears.
Repeat steps 1 to 4 using 10ml and 15ml of hydrogen peroxide.

Original Experiment's Results

Experiment	Time (minutes)
A	19.05
B	7.48
C	3.06
D	1.30
E	0.51
F	0.47
G	0.43

Modified Experiment's Results

Iodine Clock Reaction (5ml of H2O2)

Experiment	Trial 1	Trial 2	Trial 3	Trial 4	Trial 5	Trial 6
B/5	4.31	6.03	4.01	5.59	7.08	10.41
C/5	3.23	2.40	3.32	2.24	2.10	3.30
D/5	1.10	1.29	1.39	2.21	2.21	1.44
E/5	1.19	1.23	1.17	1.14	1.04	1.07

Iodine Clock Reaction (10ml of H2O2)

Experiment	Trial 1	Trial 2	Trial 3	Trial 4	Trial 5	Trial 6
B/10	4.13	3.58	2.57	4.45	4.29	3.55
C/10	1.19	2.08	2.13	1.54	2.11	2.01
D/10	0.54	0.59	1.16	0.58	0.56	1.26
E/10	0.33	0.35	0.36	0.45	0.55	0.44

Iodine Clock Reaction (15ml of H2O2)

Experiment	Trial 1	Trial 2	Trial 3	Trial 4	Trial 5	Trial 6
B/15	4.25	3.48	4.37	3.56	11.28	5.01
C/15	1.38	1.39	1.48	2.43	6.37	2.45
D/15	0.59	0.58	0.55	1.23	3.52	1.43
E/15	0.32	0.33	0.34	1.11	3.27	0.59

Calculations

Calculations used:

Standard Deviation:

SD = √[Σ(xi - x̄)² / (N - 1)]

Standard Error:

SE = SD / √N

95% Confidence Intervals:

95% CI = x̄ ± (1.96 * SE)

Iodine Clock Reaction (5ml of H2O2)

Experiment	Mean	Standard Deviation	Standard Error	95% Confidence Intervals
B/5	6.238333	2.334904	1.167452	6.238333333 ± 1.87
C/5	2.765	0.576463	0.23534	2.765 ± 0.461
D/5	1.606667	0.481608	0.196616	1.606666667 ± 0.385
E/5	1.14	0.072664	0.029665	1.14 ± 0.0581

Iodine Clock Reaction (10ml of H2O2)

Experiment	Mean	Standard Deviation	Standard Error	95% Confidence Intervals
B/10	3.761667	0.690867	0.282045	3.761666667 ± 0.553
C/10	1.843333	0.388827	0.158738	1.843333333 ± 0.311
D/10	0.781667	0.333731	0.136245	0.781666667 ± 0.267
E/10	0.413333	0.083106	0.033928	0.413333333 ± 0.0665

Iodine Clock Reaction (15ml of H2O2)

Experiment	Mean	Standard Deviation	Standard Error	95% Confidence Intervals
B/15	5.325	2.971469	1.213097	5.325 ± 2.38
C/15	2.583333	1.921954	0.784634	2.583333333 ± 1.54
D/15	1.316667	1.143113	0.466674	1.316666667 ± 0.915
E/15	0.993333	1.155832	0.471866	0.993333333 ± 0.925

Source of Error

Although precautions were taken, potential sources of error exist:

Airborne contaminants could have affected the chemicals during mixing.
Non-disinfected utensils may have introduced impurities.
Measurement using pipettes involves some degree of human error.
No equipment cleaning between chemicals could lead to unintentional mixing.

Uncertainties

Using a pipette introduced uncertainties due to a +/- 0.10mL tolerance. Temperature fluctuations also impacted accuracy. The table below illustrates temperature variations:

Day	Temperature	Difference from 100% accuracy
Wed 12th June	21.5°C	1.5°C
Fri 14th June	22°C	2°C
Tues 18th June	21°C	1°C
Thurs 20th June	22.5°C	2.5°C
Fri 21st June	23°C	3°C

This data indicates that the pipette measurements were not 100% accurate on any day.

Suggested Improvements

Possible improvements include:

Temperature monitoring and control during experiments.
Ensuring the room temperature matches the required temperature for accurate pipette measurements.
Rigorous cleaning and disinfection of all equipment to prevent contamination.

Evaluation

This experiment was valid, reliable, and controlled by maintaining constant conditions except for hydrogen peroxide concentration. The dependent variable was the time for the iodine clock reaction, while the independent variable was hydrogen peroxide concentration. The results showed that higher hydrogen peroxide concentration led to faster reactions, consistent with collision theory.

Conclusion

Increasing hydrogen peroxide concentration resulted in faster iodine clock reactions, supporting the hypothesis that concentration affects reaction rates. This aligns with collision theory, as higher concentrations increase collision frequency, leading to shorter reaction times.

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