10. A chemist conducted an experiment in which they observed a chemical reaction under various temperatures. The chemist used the same substances in the same amounts for each reaction and only varied the heat applied for each reaction. The chemist recorded the duration and primary color of each reaction. What is a control variable in this experiment?
Answer: D
The amount of each substance
In this experiment, a control variable is the amount of each substance used, as it was kept constant throughout the trials to ensure that any observed changes in the reaction could be attributed solely to the varying temperatures.
A) The primary reaction color
The primary reaction color is an outcome of the chemical reactions and is not controlled by the chemist. It varies as a result of the experiment and serves as a dependent variable rather than a control variable.
B) The amount of heat applied
The amount of heat applied is the independent variable in this experiment, as it is the factor that the chemist is actively changing to observe its effect on the reaction. Therefore, it cannot be considered a control variable.
C) The duration of each reaction
The duration of each reaction may vary depending on the temperature applied, which means it is not a control variable. Instead, it is another dependent variable whose changes are being measured in response to the independent variable.
D) The amount of each substance
The amount of each substance is a control variable because it is kept constant across all trials. This ensures that the only factor influencing the reaction is the temperature, allowing for a fair comparison of the results.
Conclusion
The correct answer is the amount of each substance, as it is the variable that remains unchanged throughout the experiment to provide a controlled environment for testing how temperature influences the reaction. All other options either represent variables that change or outcomes of the experiment, thereby failing to meet the criteria for control variables.