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Difficulty: HardDesigning Follow-Up Experiments and Test Modifications

Suppose a student wants to modify an experiment measuring the evaporation rate of salt water (200 mL200\text{ mL} of 5%5\% saline solution heated by a 100 W100\text{ W} heat lamp placed 30 cm30\text{ cm} above the beaker in a draft-free room) to determine the specific impact of wind speed on the evaporation rate, while ensuring that the thermal energy input and other variables remain controlled. Arrange the following steps in the correct chronological sequence to successfully conduct this follow-up experiment.

  1. 1Prepare three identical beakers, each containing 200 mL200\text{ mL} of 5%5\% saline solution at room temperature.
  2. 2Position the 100 W100\text{ W} heat lamp 30 cm30\text{ cm} directly above the beaker and place a variable-speed fan at a fixed distance of 50 cm50\text{ cm} from the beaker.
  3. 3Select the specific wind speed setting (low, medium, or high) for the trial, then turn on both the fan and the heat lamp simultaneously.
  4. 4Record the mass of the beaker at 1010-minute intervals over a 6060-minute period.

Answer

The correct chronological sequence is: first, prepare the three identical saline solution beakers; second, position the heat lamp and the variable-speed fan at fixed distances relative to the beaker; third, select the wind speed setting and start the fan and lamp; and fourth, record the mass of the beaker at ten-minute intervals over one hour.
The correct sequence begins with preparing the identical solutions to establish controlled initial parameters. Next, the physical apparatus must be positioned to control the heat lamp distance and fan distance. Then, the specific wind speed is chosen and the trial is started by turning on the equipment. Finally, the mass is measured at regular intervals to track the evaporation rate.

Step-by-Step Solution

1
Prepare identical samples to control initial conditions.
Three beakers with equal volume (200 mL200\text{ mL}) and concentration (5%5\%) of saline solution.
Ensures that differences in evaporation are due only to the wind speed, not variations in initial volume or salinity.
2
Set up the physical apparatus with controlled physical dimensions.
The beaker, heat lamp (30 cm30\text{ cm} away), and fan (50 cm50\text{ cm} away) are positioned in a stable, repeatable configuration.
Ensures the heat energy delivered to the solution is constant across all trials, and the fan's physical distance does not vary.
3
Apply the independent variable (wind speed) and start the experimental conditions.
The trial begins under a specific, constant wind speed with simultaneous heating.
Allows the evaporation process to begin under the selected test condition.
4
Measure and record the dependent variable over the specified duration.
Mass data at 1010, 2020, 3030, 4040, 5050, and 6060 minutes.
Provides the raw data necessary to calculate the rate of mass loss (evaporation rate) over time for that specific wind speed.

Key Concept

Designing a controlled follow-up experiment requires isolating the new independent variable (wind speed) by maintaining all original variables (lamp distance, initial salinity, and volume) constant, and sequencing the steps from sample preparation to final measurement.
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Topics

Designing Follow-Up Experiments and Test Modifications

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