Video Transcript
The image below shows three
manometers, each containing a sample of ethanoic acid. For which manometer is the
temperature of the ethanoic acid the highest?
We can use manometers to measure
the vapor pressure of pure substances. In all the manometers, we have
exactly the same amount of ethanoic acid. Above the liquid and in the tubing,
we’re going to have gaseous ethanoic acid. The other part of the manometer is
the U-shaped tube that contains a dense liquid. Here I’m assuming that it’s
mercury. If we heat the ethanoic acid in the
flask, we’re going to increase the amount of ethanoic vapor in the tubing. This is going to increase the
pressure on this side of the manometer. This vapor pressure is going to
compete with the external pressure applied to the other side of the U-shaped
tube. We can assume it’s one
atmosphere. The most important thing is that
it’s consistent between A, B, and C.
The question is asking, for which
manometer is the temperature of the ethanoic acid the highest? We can label the temperatures 𝑇 A,
𝑇 B, and 𝑇 C. The lower the level of the mercury
on the side of the flask, the higher the vapor pressure in the flask. We can put the manometers in order
of the height of the mercury on the side of the flask. The height is greatest for A and
lowest for C. This means the pressure inside C
must be the highest of the three, and the temperature of the ethanoic acid in C is
greater than the ethanoic acid in B or the ethanoic acid in A. Therefore, the manometer in which
the temperature of the ethanoic acid is the highest is C.
