Video Transcript
What is the name given to the
surface of the water indicated in the illustration by the blue arrow? (A) Tension point, (B) turbulence
dip, (C) laminar surface, (D) bounding surface, or (E) meniscus.
This question is asking us to name
the surface of the water in this illustration. When we view water in a transparent
glass tube, we can see that the surface is curved up at the tube’s edges. A key piece of information to
understand this curve is that water has high surface tension due to its hydrogen
bonds. Hydrogen bonds are a strong
intermolecular force. In water, they form between the
oxygen atom of one molecule and the hydrogen atom of another molecule.
When we say that water has a high
surface tension, we mean that it has strong intermolecular forces. These attractive forces holding
molecules together explain why water forms droplets and why water striders are able
to float on the surface of a stream. When water is in a graduated
cylinder like this one, the water molecules on the edge adhere to the surface of the
glass. And since there’s a strong
attraction between water molecules, they pull up other water molecules with
them. The end result is a raised surface
where the water and glass meet. We simply need to be familiar with
the name of this curve, which is called the meniscus. Choice (E) is the correct
answer.
The meniscus is quite relevant in
chemistry because it influences how we take measurements with glassware. It may be tempting to measure from
the top of the meniscus, like the green arrow in the illustration indicates. However, it is more accurate to
measure from the bottom of the meniscus and ignore the negligible amount of water
that has climbed up the sides of the cylinder. So we can say that chemists take
measurements from the bottom of the meniscus.
So, what is the name given to the
surface of the water in the illustration? That’s choice (E), meniscus.
