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Difficulty: MediumIdentifying Sources of Error and Confounding Variables

A researcher is reviewing several experimental setups to ensure that all potential confounding variables are properly controlled. Match each experimental procedure to the specific uncontrolled variable or source of error that threatens the validity of its findings.

  • Measuring how the length of a pendulum string affects its period of oscillation, while releasing the pendulum bob from a different starting angle for each length tested.Varying the initial potential energy and amplitude of the swing, which can alter the period if the angle is large.
  • Comparing how quickly different solutes dissolve in water, while stirring the mixture rapidly for some solutes and leaving others completely still.Inconsistently introducing kinetic energy and convective transport, which accelerates dissolution rates independently of solute solubility.
  • Measuring the rate of water drainage through different soil types, while packing the soil samples to different densities in their columns.Modifying the volume of pore space and flow resistance, which alters drainage speed independently of soil composition.
  • Investigating osmosis by placing potato cylinders in sucrose solutions of different concentrations, while using potato cylinders cut to different surface-area-to-volume ratios.Altering the relative exposure area for water transport, which changes the rate of diffusion per unit volume regardless of concentration gradients.

Answer

The pendulum length experiment matches the starting angle confound; the solute dissolution experiment matches the stirring rate confound; the soil permeability experiment matches the compaction density confound; and the potato osmosis experiment matches the surface-area-to-volume ratio confound.
Each experimental setup introduces a specific uncontrolled variable that interferes with the relationship between the independent and dependent variables. By matching the physical properties of the error to the specific experimental system, we identify how each confounding factor compromises the results.

Step-by-Step Solution

1
Analyze each experimental procedure to identify the independent variable and the intended dependent variable.
For each setup, the independent variable (pendulum length, solute type, soil type, sucrose concentration) is varied to measure a dependent variable (period, dissolution speed, drainage rate, osmosis rate).
Understanding the intended relationship helps pinpoint variables that should be controlled but are instead being varied.
2
Identify the uncontrolled variable in each procedure that varies alongside the independent variable.
The uncontrolled variables are: starting angle (pendulum), stirring rate (dissolution), packing density (soil drainage), and cylinder dimensions/surface-area-to-volume ratio (osmosis).
An uncontrolled variable that changes systematically with the independent variable is a confounding variable.
3
Match each uncontrolled variable to its physical consequence on the experimental measurement.
Starting angle affects potential energy/amplitude; stirring affects convective transport/dissolution rate; packing density affects pore space/flow resistance; surface-area-to-volume ratio affects diffusion rate per unit volume.
This establishes the physical mechanism by which the confounding variable compromises the validity of the results.

Key Concept

Identifying Sources of Error and Confounding Variables
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Topics

Identifying Sources of Error and Confounding Variables

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