Question

Allen pours water into a graduated cylinder. He notices that the surface of the water is curved, as shown below.

Graduated cylinder showing curved surface of water where the sides of the water are higher than the center
Graduated cylinder showing curved surface of water where the sides of the water are higher than the center
Which of the following identifies this phenomenon and explains how it is formed?
Choose 1 answer:
Choose 1 answer:
(Choice A, Incorrect) The curved surface is a concave meniscus which has formed because of surface tension.
INCORRECT
The curved surface is a concave meniscus which has formed because of surface tension.
The concave meniscus is formed due to capillary action, not surface tension.
(Choice B, Incorrect) The curved surface is a convex meniscus which has formed because of capillary action.
INCORRECT
The curved surface is a convex meniscus which has formed because of capillary action.
Because the water has moved upward along the sides of the glass, a concave meniscus has formed.
(Choice C, Checked, Correct) The curved surface is a concave meniscus which has formed because of capillary action.
CORRECT (SELECTED)
The curved surface is a concave meniscus which has formed because of capillary action.
Capillary action occurs because the water molecules are more attracted to the cylinder than they are to each other. This causes the upward movement of the water along the sides of the glass, forming a curved surface called a concave meniscus.
(Choice D, Incorrect) The curved surface is a convex meniscus which has formed because of surface tension.
INCORRECT
The curved surface is a convex meniscus which has formed because of surface tension.
Because the water has moved upward along the sides of the glass, a concave meniscus has formed. In addition, this is due to capillary action, rather than surface tension.

Answer 1

The concave meniscus formed by water in a graduated cylinder is due to capillary action resulting from water's strong adhesion to glass outweighing its cohesion, leading to an upward curve along the edges.

Step-by-step explanation:

The curved surface of water in a graduated cylinder that is higher at the edges than at the center is known as a concave meniscus. This shape is caused by capillary action, which is the result of water’s strong adhesive forces with the polar surface of the glass creating an upward force that allows the water to climb up the sides of the container. This adherence of water to glass is stronger than the cohesive forces within the water itself. Since a graduated cylinder contains a polar surface similar to glass, water forms a concave meniscus inside the cylinder as it rises along the edges due to the adhesion between water molecules and the polar SiOH groups on the glass surface.

Conversely, substances like mercury, which have stronger cohesive forces than adhesive forces with glass, form a convex meniscus because the mercury molecules are more attracted to each other than to the glass, resulting in a downward curve. Surface tension in water is high due to hydrogen bonding, and it contributes to the curvature of the meniscus, but the specific concave shape is primarily caused by the interplay between adhesive and cohesive forces described by capillary action.