Examkin

Question

Difficulty: MediumFormulating and Modifying Hypotheses

A student proposed the following hypothesis regarding the decomposition of hydrogen peroxide (H2O2H_2O_2) in the presence of the catalyst catalase:

*Hypothesis*: The rate of H2O2H_2O_2 decomposition increases linearly as the concentration of catalase increases, because more catalyst molecules are available to speed up the reaction.

To test this hypothesis, the student measured the rate of oxygen (O2O_2) gas production (in mL/min) at various catalase concentrations (in percent, %\%) while keeping the substrate concentration and temperature constant. The results are shown in the table below:

Catalase concentration (%\%)O2O_2 production rate (mL/min)
0.00.0
1.05.4
2.010.8
3.016.2
4.016.3
5.016.3

Based on these results, how should the student modify the hypothesis?

  1. A
    The hypothesis should be modified to state that the reaction rate is inversely proportional to catalase concentration at all tested concentrations.
  2. B
    The hypothesis should be modified to state that the reaction rate increases continuously without limit as catalase concentration increases.
  3. The hypothesis should be modified to state that the reaction rate increases linearly with catalase concentration up to a threshold, above which the rate remains constant.Answer
  4. D
    The hypothesis should be modified to state that the reaction rate decreases once the catalase concentration exceeds 3.0\%.

Answer

The hypothesis should be modified to state that the reaction rate increases linearly with catalase concentration up to a threshold, above which the rate remains constant.
The experimental results demonstrate a linear relationship between catalase concentration and oxygen production rate from 0.0\% to 3.0\%, with the rate increasing by exactly 5.4 mL/min for each 1.0\% increase in concentration. However, at concentrations of 4.0\% and 5.0\%, the rate levels off and remains nearly constant at 16.3 mL/min. The correct option reflects this transition by stating that the rate increases linearly up to a threshold (around 3.0\%), after which it remains constant.

Step-by-Step Solution

1
Analyze the student's initial hypothesis.
The initial hypothesis predicts a linear, unlimited increase in the reaction rate as the catalase concentration increases.
To evaluate a hypothesis, we must first identify its specific predictions.
2
Examine the relationship between catalase concentration and oxygen production rate in the data table.
From 0.0\% to 3.0\% catalase, the rate increases linearly by 5.4 mL/min for every 1.0\% increase in catalase concentration (0.0→5.4→10.8→16.20.0 \rightarrow 5.4 \rightarrow 10.8 \rightarrow 16.2).
This step determines the range over which the original hypothesis holds true.
3
Analyze the trend in the data table above the 3.0\% catalase concentration.
At 4.0\% and 5.0\% catalase, the rate remains constant at approximately 16.3 mL/min.
Identifying where the data deviates from the predicted trend shows how the hypothesis must be modified.
4
Synthesize the two trends to modify the hypothesis.
The rate increases linearly up to 3.0\% (a threshold) and then plateaus, meaning the hypothesis must be modified to include this threshold and constant behavior.
This produces the final modified hypothesis that is fully supported by all experimental data.

Key Concept

Modifying a hypothesis to align with data that shows a transition from a linear increase to a plateau (saturation effect).
Estimated Time:1m 30s
Rate this question

Topics

Formulating and Modifying Hypotheses

More questions from this topic