A marine geochemist conducted an experiment to evaluate the effect of ocean depth on the d… — ACT

A marine geochemist conducted an experiment to evaluate the effect of ocean depth on the dissolution rate of calcium carbonate ( $\text{CaCO}_3$ ). Four sealed pressure vessels were filled with seawater kept at a constant temperature of $2^\circ\text{C}$ and a fixed salinity of $35\text{ psu}$ . The hydrostatic pressure in each vessel was set to a different specific level: $100\text{ atm}$ , $200\text{ atm}$ , $300\text{ atm}$ , or $400\text{ atm}$ . A synthetic calcite pellet with an initial mass of $5.00\text{ g}$ was placed in each vessel. After $48\text{ hours}$ , the pellet was removed and weighed to determine the total mass of dissolved $\text{CaCO}_3$ (in milligrams). Which of the following correctly identifies the independent variable and one of the controlled variables in this experiment?

The independent variable is the hydrostatic pressure, and a controlled variable is the seawater temperature.Answer
B
The independent variable is the mass of dissolved $\text{CaCO}_3$ , and a controlled variable is the hydrostatic pressure.
C
The independent variable is the hydrostatic pressure, and a controlled variable is the mass of dissolved $\text{CaCO}_3$ .
D
The independent variable is the seawater temperature, and a controlled variable is the salinity.

Answer

The independent variable is the hydrostatic pressure, and a controlled variable is the seawater temperature.

In experimental design, the independent variable is the factor deliberately altered by the experimenter (hydrostatic pressure), the dependent variable is the measured outcome (mass of dissolved

\text{CaCO}_3

), and controlled variables are kept constant across all trials (seawater temperature, salinity, initial pellet mass, and time). Therefore, hydrostatic pressure is the independent variable, and seawater temperature is a controlled variable.

Step-by-Step Solution

Identify the variable that the researcher explicitly changes or manipulates between experimental trials.

The hydrostatic pressure was deliberately altered across four distinct levels (

100\text{ atm}

200\text{ atm}

300\text{ atm}

, and

400\text{ atm}

), making hydrostatic pressure the independent variable.

The independent variable is the factor systematically varied by the investigator to test its effects.

Identify the factor measured as an outcome of the experimental conditions.

The total mass of dissolved

\text{CaCO}_3

was measured after

48\text{ hours}

, making it the dependent variable.

The dependent variable represents the responding measurement or data collected.

Identify parameters held constant across all trials to prevent confounding effects.

Seawater temperature (

2^\circ\text{C}

), salinity (

35\text{ psu}

), pellet initial mass (

5.00\text{ g}

), and reaction duration (

48\text{ hours}

) were kept constant, making each of them controlled variables.

Controlled variables must be held identical across treatments so that changes in the dependent variable can be attributed solely to the independent variable.

Key Concept

Identifying Independent, Dependent, and Controlled Variables

Question

Answer

Step-by-Step Solution

Key Concept

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