In a baseline experiment, a chemist measured the rate of hydrogen peroxide (H_2O_2) decomp… — ACT

In a baseline experiment, a chemist measured the rate of hydrogen peroxide ( $H_2O_2$ ) decomposition by adding $1.0\text{ g}$ of manganese dioxide ( $MnO_2$ ) to $100\text{ mL}$ of a $3\%\text{ }H_2O_2$ solution at $25^\circ\text{C}$ and recording the volume of oxygen ( $O_2$ ) gas produced over $5\text{ minutes}$ . The chemist wants to design a follow-up experiment to determine how temperature affects this reaction rate, while ensuring that the concentration of reactants, catalyst mass, and total volume remain controlled. Place the following steps in the correct chronological order to successfully perform this follow-up experiment.

1Pour $100\text{ mL}$ of $3\%\text{ }H_2O_2$ solution into each of four separate, identical reaction flasks.
2Submerge the reaction flasks in water baths set to different temperatures ( $10^\circ\text{C}$ , $25^\circ\text{C}$ , $40^\circ\text{C}$ , and $55^\circ\text{C}$ ) and allow them to reach thermal equilibrium.
3Add exactly $1.0\text{ g}$ of $MnO_2$ catalyst to each of the flasks to initiate the decomposition reaction.
4Record the volume of $O_2$ gas produced at $1\text{-minute}$ intervals for a total of $5\text{ minutes}$ .

Answer

The correct sequence of steps is: prepare the identical hydrogen peroxide solutions, adjust their temperatures in the different water baths, add the manganese dioxide catalyst to initiate the reaction, and then measure the oxygen gas volume produced over the five-minute interval.

The correct sequence starts with preparing the identical solutions, then bringing them to the target temperatures. The catalyst must only be added after the temperatures are established to ensure the entire reaction occurs at the target temperature. Finally, the volume of gas produced is measured to determine the rate.

Step-by-Step Solution

Identify the independent variable (temperature) and the controlled variables (reactants concentration, volume, and catalyst mass).

The setup must isolate temperature as the only variable that changes before the reaction begins.

To accurately measure the effect of temperature on the rate of decomposition.

Sequence the steps such that temperature is controlled before the reaction is initiated.

The solutions must be prepared and brought to their target temperatures prior to adding the catalyst.

Adding the catalyst first would start the reaction at an uncontrolled, transitional temperature.

Determine the final phase of the experiment.

Adding the catalyst starts the reaction, immediately followed by the measurement of gas volume.

The rate is determined by measuring gas production over time once the reaction is active.

Key Concept

Isolating the independent variable in a modified experimental procedure by establishing controlled conditions and adjusting the independent variable before initiating the reaction.

Estimated Time:1m 30s

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