A student performed an experiment to study the catalytic decomposition of hydrogen peroxid… — ACT

A student performed an experiment to study the catalytic decomposition of hydrogen peroxide ( $H_2O_2$ ). In 5 separate trials, the student added $5\text{ mL}$ of a ferric nitrate ( $Fe(NO_3)_3$ ) solution of varying concentrations ( $0.1\text{ M}$ , $0.2\text{ M}$ , $0.3\text{ M}$ , $0.4\text{ M}$ , and $0.5\text{ M}$ ) to $50\text{ mL}$ of $3\%\text{ }H_2O_2$ solution in a sealed reaction flask connected to a gas syringe. The initial temperature of all solutions was maintained at $22^\circ\text{C}$ . For each trial, the volume of oxygen gas ( $O_2$ ) produced in the first $30\text{ seconds}$ was recorded to determine the initial reaction rate.

Based on the experimental procedure described, which of the following was the independent variable in the student's experiment?

Concentration of the ferric nitrate solutionAnswer
B
Volume of oxygen gas produced in the first $30\text{ seconds}$
C
Initial temperature of the reaction solutions
D
Volume of hydrogen peroxide solution added to the flask

Answer

The concentration of the ferric nitrate solution is the independent variable because it is the factor purposefully altered across trials by the researcher.

The correct answer identifies the concentration of the ferric nitrate solution because it is the factor purposefully manipulated across the 5 trials (

0.1\text{ M}

0.5\text{ M}

) to observe its effect on the rate of gas production.

Step-by-Step Solution

Identify the variable manipulated by the experimenter across trials.

The concentration of ferric nitrate (

Fe(NO_3)_3

) was systematically varied from

0.1\text{ M}

0.5\text{ M}

The independent variable is the factor directly and intentionally changed by the investigator.

Distinguish the independent variable from the dependent variable and controlled variables.

The volume of

O_2

produced is the dependent variable (measured outcome), while temperature and

H_2O_2

volume are controlled variables (held constant).

A clear separation of experimental roles is necessary to establish cause-and-effect relationships.

Key Concept

Independent vs. Dependent vs. Controlled Variables

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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