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Difficulty: MediumFormulating and Modifying Hypotheses

An environmental scientist investigated the relationship between water temperature and the concentration of dissolved oxygen (DO) at saturation. The scientist hypothesized that as water temperature increases, the concentration of DO at saturation also increases because higher temperatures increase the solubility of gases in water. To test this hypothesis, the scientist measured the DO concentration at saturation in water samples at five different temperatures. The results are presented in the table below.

Water Temperature (∘C^\circ\text{C})Dissolved Oxygen Concentration (mg/L\text{mg/L})
5512.812.8
151510.110.1
25258.38.3
35356.96.9
45455.95.9

Based on these results, does the data support the scientist's hypothesis, and how should the hypothesis be revised?

  1. No; the revised hypothesis should state that as water temperature increases, the concentration of dissolved oxygen at saturation decreases.Answer
  2. B
    Yes; the revised hypothesis should state that as water temperature increases, the concentration of dissolved oxygen at saturation increases.
  3. C
    No; the revised hypothesis should state that changing the concentration of dissolved oxygen at saturation causes the water temperature to decrease.
  4. D
    No; the revised hypothesis should state that the concentration of dissolved oxygen at saturation remains constant regardless of water temperature.

Answer

No; the revised hypothesis should state that as water temperature increases, the concentration of dissolved oxygen at saturation decreases.
The scientist's hypothesis predicted that as temperature increases, the concentration of dissolved oxygen at saturation would also increase. However, the experimental results show that as the temperature increases from 5∘C5^\circ\text{C} to 45∘C45^\circ\text{C}, the concentration of dissolved oxygen decreases from 12.8 mg/L12.8\text{ mg/L} to 5.9 mg/L5.9\text{ mg/L}. Because the results show the opposite of the predicted trend, the hypothesis is not supported, and the revised hypothesis must state that as water temperature increases, the concentration of dissolved oxygen at saturation decreases.

Step-by-Step Solution

1
Identify the scientist's original hypothesis and its predicted outcome.
The original hypothesis predicts that an increase in water temperature results in an increase in dissolved oxygen (DO) concentration (a direct relationship).
Establishing the initial prediction allows direct comparison with the actual experimental data.
2
Analyze the trend shown in the experimental data table.
As the temperature increases from 5∘C5^\circ\text{C} to 45∘C45^\circ\text{C}, the DO concentration steadily decreases from 12.8 mg/L12.8\text{ mg/L} to 5.9 mg/L5.9\text{ mg/L} (an inverse relationship).
Determining the actual mathematical relationship between the variables reveals if the initial prediction was correct.
3
Determine if the hypothesis is supported and formulate the necessary revision.
The data contradicts the hypothesis, meaning it is not supported (No). The hypothesis must be revised to reflect the inverse trend: as water temperature increases, DO concentration at saturation decreases.
Hypotheses must be modified to align with experimental findings when those findings refute the initial prediction.

Key Concept

Formulating and Modifying Hypotheses
Estimated Time:1m 30s
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Topics

Formulating and Modifying Hypotheses

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