Researchers studied the effect of dissolved organic carbon (DOC) on the photochemical degr… — ACT

Researchers studied the effect of dissolved organic carbon (DOC) on the photochemical degradation rate of Pollutant X in water samples exposed to constant UV light. Two initial hypotheses were proposed:

* Hypothesis 1: DOC acts as a photosensitizer, so increasing DOC concentration will continuously increase the degradation rate of Pollutant X.
* Hypothesis 2: DOC acts as a light attenuator (blocking UV light), so increasing DOC concentration will continuously decrease the degradation rate of Pollutant X.

The degradation rate of Pollutant X was measured at various DOC concentrations, and the results are recorded in the table below:

DOC Concentration ( $\text{mg/L}$ )	Degradation Rate (\%\text{ per hour})
$0$	$5.2$
$2$	$8.4$
$4$	$11.1$
$8$	$9.5$
$12$	$6.8$
$16$	$4.3$

Based on these results, which of the following modified hypotheses best describes the relationship between DOC concentration and the degradation rate of Pollutant X?

A
DOC acts as a light attenuator across all tested concentrations, meaning the degradation rate of Pollutant X decreased continuously as DOC concentration increased from $0\text{ mg/L}$ to $16\text{ mg/L}$ .
B
DOC has no effect on the degradation rate of Pollutant X, meaning the rate remains constant at approximately $11.1\%\text{ per hour}$ regardless of changes in DOC concentration.
DOC increases the degradation rate of Pollutant X at low concentrations (up to $4\text{ mg/L}$ ) by acting as a photosensitizer, but decreases the rate at higher concentrations (above $4\text{ mg/L}$ ) due to light attenuation.Cevap
D
DOC acts as a photosensitizer across all concentrations, meaning the degradation rate of Pollutant X will continuously increase as the DOC concentration is raised beyond $4\text{ mg/L}$ .

Cevap

Dissolved organic carbon (DOC) increases the degradation rate of Pollutant X at low concentrations (up to

4\text{ mg/L}

) by acting as a photosensitizer, but decreases the rate at higher concentrations (above

4\text{ mg/L}

) due to light attenuation.

The correct hypothesis must account for the biphasic trend observed in the data. The degradation rate of Pollutant X rises from

5.2\%\text{ per hour}

11.1\%\text{ per hour}

as the dissolved organic carbon (DOC) concentration increases from

0\text{ mg/L}

4\text{ mg/L}

, supporting the photosensitizer role (Hypothesis 1). However, as the DOC concentration increases further from

4\text{ mg/L}

16\text{ mg/L}

, the degradation rate steadily decreases to

4.3\%\text{ per hour}

, which supports the light attenuator role (Hypothesis 2). Combining these two effects into a single modified hypothesis correctly explains the entire range of data.

Adım Adım Çözüm

Analyze the trend in the degradation rate of Pollutant X as the DOC concentration increases from

0\text{ mg/L}

4\text{ mg/L}

The degradation rate increases from

5.2\%\text{ per hour}

11.1\%\text{ per hour}

To determine if the initial phase of the reaction supports the photosensitizer hypothesis.

Analyze the trend in the degradation rate as the DOC concentration increases from

4\text{ mg/L}

16\text{ mg/L}

The degradation rate decreases from

11.1\%\text{ per hour}

4.3\%\text{ per hour}

To determine if the subsequent phase of the reaction supports the light attenuator hypothesis.

Synthesize these observations to evaluate the proposed hypotheses and formulate a modified hypothesis.

A modified hypothesis must state that DOC acts as a photosensitizer at low concentrations but as a light attenuator at high concentrations, matching both trends.

To find the option that correctly describes this dual behavior across the entire range.

Anahtar Kavram

Evaluating and modifying scientific hypotheses based on experimental data that exhibit non-linear or multi-phase relationships.

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