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Chapter 13: Problem 8

You take a sample of water that is at room temperature and in contact with air and put it under a vacuum. Right away, you see bubbles leave the water, but after a little while, the bubbles stop. As you keep applying the vacuum, more bubbles appear. A friend tells you that the first bubbles were water vapor, and the low pressure had reduced the boiling point of water, causing the water to boil. Another friend tells you that the first bubbles were gas molecules from the air (oxygen, nitrogen, and so forth) that were dissolved in the water. Which friend is mostly likely to be correct? What, then, is responsible for the second batch of bubbles? [Section 13.4]

Short Answer

Expert verified
The first friend is most likely to be correct, as the first bubbles observed were probably dissolved gases (oxygen, nitrogen, etc.) coming out of the solution due to the decreased pressure above the water. The second batch of bubbles was likely caused by the boiling of water due to the reduced boiling point under vacuum.

Step by step solution

01

Understanding the effect of vacuum on water

When water is put under a vacuum, the pressure above the water decreases. This causes a decrease in the boiling point of water, allowing it to boil at a lower temperature.
02

Dissolved gases in water

Certain gases, particularly oxygen and nitrogen, have the ability to dissolve in water. These gases can be released from the water when the conditions change, such as when the pressure above the water decreases.
03

Identifying the cause of the first bubbles

Given that the water was at room temperature and in contact with air initially, it is likely that there were dissolved gases (oxygen, nitrogen, etc.) in the water. When the vacuum was applied, the pressure above the water decreased significantly, causing the dissolved gases in the water to come out of solution and form bubbles. This means the first friend, who claimed that the first bubbles were gas molecules from the air that were dissolved in the water, is mostly likely to be correct.
04

Identifying the cause of the second batch of bubbles

As the vacuum continues to be applied, the boiling point of water decreases even further. At this point, the temperature of the water is equal to or above the new boiling point, causing the water to boil and produce water vapor bubbles. This means that the second batch of bubbles is likely caused by the boiling of water due to the reduced boiling point under vacuum. In conclusion, the first friend is most likely to be correct, as the first bubbles observed were most likely dissolved gases, particularly oxygen and nitrogen, coming out of the solution. The second batch of bubbles was most likely caused by the boiling of water due to the reduced boiling point under vacuum.

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