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Question Video: Indicating the Temperature of Ethanoic Acid Using Manometers Chemistry

The image shows three manometers, each containing a sample of ethanoic acid. For which manometer is the temperature of the ethanoic acid the highest?

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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.

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