Carlos set up three full vials beside one another and added drops to see the surface tensions of three different liquids. Which event could be a source of error?
A. The air temperature varied when someone opened a window.
B. The liquids that spilled over the edges could mix on the table.
C. The vials were different shapes.
D. The vials were made of the same material.
The correct answer and explanation is:
Correct Answer: C. The vials were different shapes.
Explanation:
Carlos is conducting an experiment to compare the surface tension of three different liquids by observing how many drops can be added to each vial before the liquid spills over. Surface tension is a property of a liquid that allows it to resist external forces due to cohesive forces among its molecules.
For this kind of experiment to be accurate, all external and container-related factors must be controlled or kept the same—except for the liquid being tested.
Let’s evaluate each option:
- A. The air temperature varied when someone opened a window.
While temperature can influence surface tension, minor fluctuations from a brief window opening are unlikely to drastically change the results in a short, controlled experiment. Still, it’s a possible but minor source of error. - B. The liquids that spilled over the edges could mix on the table.
This doesn’t affect the measurement of surface tension inside each vial. The key measurement ends when the surface breaks, so mixing on the table has no bearing. - C. The vials were different shapes.
This is the best answer. The shape of the vial affects how the surface curves at the top (meniscus shape) and how many drops it can hold before spilling. A wide mouth may hold more liquid than a narrow one, not because of surface tension, but due to geometry. Therefore, using different-shaped vials introduces a major variable that distorts the results. - D. The vials were made of the same material.
This is a good practice, not a source of error. Having the same material ensures consistent adhesion between the liquid and container surface.
Conclusion:
Using vials of different shapes can lead to incorrect conclusions about surface tension, as the container geometry alters how drops accumulate and spill. This makes Option C the most significant source of error in Carlos’s experiment.