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Difficulty: MediumFormulating and Modifying Hypotheses

A student hypothesized that as the concentration of dissolved carbon dioxide (CO2\text{CO}_2) in water increases, the pH of the solution will increase. To test this, the student bubbled different volumes of CO2\text{CO}_2 gas into 100 mL samples of distilled water at 25∘C25^\circ\text{C} and measured the pH of each sample. The results are shown in the table below:

SampleVolume of CO2\text{CO}_2 bubbled (mL)pH of solution
107.0
2106.2
3205.8
4305.5
5405.3

Based on these results, which of the following represents the most appropriate modification to the student's hypothesis?

  1. Modify the hypothesis to state that as the concentration of dissolved CO2\text{CO}_2 increases, the pH of the solution decreases.Answer
  2. B
    Modify the hypothesis to state that as the concentration of dissolved CO2\text{CO}_2 increases, the pH of the solution remains constant.
  3. C
    Modify the hypothesis to state that as the concentration of dissolved CO2\text{CO}_2 decreases, the pH of the solution decreases.
  4. D
    Modify the hypothesis to state that there is no relationship between the concentration of dissolved CO2\text{CO}_2 and the pH of the solution.

Answer

Modify the hypothesis to state that as the concentration of dissolved carbon dioxide increases, the pH of the solution decreases.
The correct answer is correct because the experimental data in the table demonstrate a clear trend: as the volume of carbon dioxide bubbled into the water increases from 0 mL to 40 mL, the pH of the solution decreases from 7.0 to 5.3. Since bubbling carbon dioxide increases the dissolved concentration of the gas, the student must modify the hypothesis to reflect this inverse relationship.

Step-by-Step Solution

1
Analyze the student's initial hypothesis regarding the relationship between carbon dioxide concentration and pH.
The initial hypothesis states that an increase in dissolved carbon dioxide concentration will cause the pH of the solution to increase.
Establishing the initial prediction allows for a direct comparison with the collected data to see if a modification is necessary.
2
Examine the experimental data in the table to determine the actual relationship between the independent variable (volume of bubbled carbon dioxide) and the dependent variable (pH).
As the volume of bubbled carbon dioxide increases from 0 mL to 40 mL, the measured pH of the solution decreases from 7.0 to 5.3.
Determining the observed relationship from the data provides the basis for correcting the hypothesis.
3
Compare the initial hypothesis to the observed trend and formulate the correct modification.
The hypothesis predicted a direct relationship (pH increases as concentration increases), but the data show an inverse relationship (pH decreases as concentration increases). Thus, the student should modify the hypothesis to state that increasing dissolved carbon dioxide concentration decreases the pH.
A scientific hypothesis must be modified to align with the empirical evidence obtained from the experiment.

Key Concept

Formulating and Modifying Hypotheses
Estimated Time:1m 0s
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Topics

Formulating and Modifying Hypotheses

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