Students conducted two experiments to study the decomposition of hydrogen peroxide (H_2O_2… — ACT

Students conducted two experiments to study the decomposition of hydrogen peroxide ( $H_2O_2$ ) into water and oxygen gas ( $O_2$ ) in the presence of a yeast catalyst suspension.

Experiment 1
A test tube was filled with $10\text{ mL}$ of $3\%$ $H_2O_2$ solution. A yeast suspension with a concentration of $1.0\text{ g/L}$ was prepared. The students added $1\text{ mL}$ of the yeast suspension to the test tube at a temperature of $25^\circ\text{C}$ and measured the volume of $O_2$ gas produced over $5\text{ minutes}$ . This procedure was repeated at temperatures of $35^\circ\text{C}$ , $45^\circ\text{C}$ , and $55^\circ\text{C}$ .

Experiment 2
Using the same apparatus at a constant temperature of $35^\circ\text{C}$ , the students added $1\text{ mL}$ of yeast suspensions of varying concentrations ( $0.5\text{ g/L}$ , $1.0\text{ g/L}$ , $1.5\text{ g/L}$ , and $2.0\text{ g/L}$ ) to separate test tubes, each containing $10\text{ mL}$ of $3\%$ $H_2O_2$ solution. The volume of $O_2$ gas produced was measured over $5\text{ minutes}$ .

Based on the experimental designs described, is the statement that the concentration of the yeast suspension served as the independent variable in Experiment 1 and as a controlled variable in Experiment 2 true or false?

Answer: Answer

Answer

False

The correct answer is false because the roles of the variables are reversed in the statement. In Experiment 1, the concentration of the yeast suspension was maintained constant at

1.0\text{ g/L}

(making it a controlled variable), whereas in Experiment 2, the concentration of the yeast suspension was varied (making it the independent variable).

Step-by-Step Solution

Identify the independent variable (the factor changed by the investigator) and the controlled variables (factors kept constant) in Experiment 1.

In Experiment 1, the temperature was varied (

25^\circ\text{C}

35^\circ\text{C}

45^\circ\text{C}

, and

55^\circ\text{C}

), which means temperature is the independent variable. The yeast suspension concentration was kept constant at

1.0\text{ g/L}

, which means it is a controlled variable.

Understanding the design of Experiment 1 requires categorizing the variables correctly.

Identify the independent variable and the controlled variables in Experiment 2.

In Experiment 2, the temperature was held constant at

35^\circ\text{C}

(controlled variable), while the concentration of the yeast suspension was varied (

0.5\text{ g/L}

1.0\text{ g/L}

1.5\text{ g/L}

, and

2.0\text{ g/L}

), making it the independent variable.

Understanding the design of Experiment 2 requires categorizing its variables correctly.

Compare the roles of the yeast concentration variable in both experiments to the proposed statement.

The statement claims that yeast concentration was the independent variable in Experiment 1 and the controlled variable in Experiment 2. Since Experiment 1 kept yeast concentration constant (controlled variable) and Experiment 2 varied it (independent variable), the statement is incorrect. The correct answer is false.

Comparing the actual experimental roles to the statement determines its truth value.

Key Concept

Comparing and Contrasting Multiple Experimental Designs

Estimated Time:1m 30s

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