Demonstrate Understanding of Important Components of Scientific Research Practice Test

A study tested whether adding a chelating agent affects the rate of an Fe$^{3+}$-catalyzed oxidation reaction. Hypothesis: EDTA decreases the oxidation rate by binding Fe$^{3+}$ and reducing its catalytic availability. Methods: Two reaction mixtures were prepared with identical concentrations of substrate and Fe$^{3+}$ at the same pH and temperature. Condition 1: no EDTA. Condition 2: added EDTA. Product formation was tracked by absorbance. Results: The EDTA condition showed a slower increase in absorbance. Which factor most likely influences the outcome?

An analytical lab evaluated the hypothesis that a pH indicator’s color change range depends on temperature. They prepared identical buffer solutions at pH 6.0 and added the same concentration of bromothymol blue. One sample was held at 10°C and the other at 40°C, then absorbance at 620 nm was recorded. The 40°C sample showed a slightly different absorbance than the 10°C sample. Which hypothesis best aligns with the study's design?