Question

Tom is in his chemistry class and notices that the water in his test tube forms a "U" shape (meniscus) on the top surface. What reasonable conclusion can be made based on this information?

1) The test tube is made of polar molecules.
2) Atmospheric pressure is pushing down more on the center than on the sides.
3) Test tubes are rounded at the bottom so the center of the water column will be lower than the sides.
4) The test tube needs more water to make it level.

Answer 1

Tom's observation of a 'U' shaped meniscus in water is due to the adhesive forces between the polar water molecules and the glass and the surface tension from cohesive forces in water, which result in a concave meniscus.

Step-by-step explanation:

When Tom observes the water forming a meniscus in his test tube, he is witnessing the effects of surface tension and the interaction between water molecules and the container. The water forms a concave meniscus because of the water's adhesive forces to the polar Si-OH groups in the glass being stronger than the water's cohesive forces. This adhesion pulls the water up the sides of the container, while the cohesion of water due to hydrogen bonding is seen in the overall high surface tension of the water, contributing to the curved shape of the meniscus. This explains why the correct reasonable conclusion based on this information is that polar substances like water display concave menisci.