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Difficulty: EasyIdentifying Independent, Dependent, and Controlled Variables

A student conducted an experiment to determine how the temperature of a reactant solution affects the rate of a chemical reaction. The student placed equal volumes of 1.0 M1.0\text{ M} hydrochloric acid (HCl\text{HCl}) in five identical beakers. Each beaker was maintained at a different temperature (10∘C10^\circ\text{C}, 20∘C20^\circ\text{C}, 30∘C30^\circ\text{C}, 40∘C40^\circ\text{C}, or 50∘C50^\circ\text{C}). The student then added a 1.0 g1.0\text{ g} strip of magnesium ribbon to each beaker and recorded the time it took for the magnesium ribbon to completely dissolve. Based on this description, which of the following was the independent variable in the experiment?

  1. A
    The time required for the magnesium ribbon to dissolve
  2. B
    The concentration of the hydrochloric acid
  3. The temperature of the hydrochloric acid solutionAnswer
  4. D
    The mass of the magnesium ribbon added

Answer

The temperature of the hydrochloric acid solution
The temperature of the hydrochloric acid solution is the independent variable because it is the condition that the student intentionally varies across the five beakers (10∘C10^\circ\text{C} to 50∘C50^\circ\text{C}) to see how it affects the reaction rate.

Step-by-Step Solution

1
Identify the factor that is intentionally changed by the student across the trials.
The temperature of the hydrochloric acid solution is varied (10∘C10^\circ\text{C}, 20∘C20^\circ\text{C}, 30∘C30^\circ\text{C}, 40∘C40^\circ\text{C}, and 50∘C50^\circ\text{C}).
The independent variable is the factor that the experimenter manipulates to test its effects.
2
Identify the factor that is measured in response to those changes.
The time it takes for the magnesium ribbon to completely dissolve is recorded.
The dependent variable is the measured result or outcome of the experiment.
3
Identify the factors that are kept constant to ensure a fair test.
The concentration of the acid (1.0 M1.0\text{ M}) and the mass of the magnesium ribbon (1.0 g1.0\text{ g}) are kept the same in each trial.
Controlled variables are parameters that must be held constant so they do not interfere with the relationship between the independent and dependent variables.

Key Concept

The independent variable is the factor manipulated by the experimenter, the dependent variable is the measured outcome, and controlled variables are kept constant.
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Topics

Identifying Independent, Dependent, and Controlled Variables

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