Chemistry Practice Problems Henry's Law Practice Problems Solution: You take a sample of water that is at room tempera...

# Solution: 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.What, then, is responsible for the second batch of bubbles?

###### Problem

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.

What, then, is responsible for the second batch of bubbles?

###### Solution

We’re being asked to determine what causes the second bubbles to form in the given sample of water. Recall that the solubility of a gas is given by Henry’s law:

$\overline{){{\mathbf{S}}}_{{\mathbf{gas}}}{\mathbf{=}}{{\mathbf{k}}}_{{\mathbf{H}}}{{\mathbf{P}}}_{{\mathbf{gas}}}}$

where Sgas = solubility of the gas (in mol/L or M), kH = Henry’s law constant for the gas, Pgas = partial pressure of the gas.

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Henry's Law

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