At 16.5°C and 1 atm, oxygen has as solubility of 1.00 mg/100g water. When air is equilibrated with a 200 g sample of water at this temperature and pressure, how many milligrams of oxygen gas are dissolved? (Assume that air contains 21 mol % oxygen.)

I thought this was a henry's law problem but apparently I am wrong someone please help.

Question

At 16.5°C and 1 atm, oxygen has as solubility of 1.00 mg/100g water. When air is equilibrated with a 200 g sample of water at this temperature and pressure, how many milligrams of oxygen gas are dissolved? (Assume that air contains 21 mol % oxygen.)  

I thought this was a henry's law problem but apparently I am wrong someone please help.

anonymous · Answer

It's just a solubility to saturated solution composition problem.   The amount in a saturated solution must equal the solubility times the amount of solution.  You're overthinking it.

anonymous · Answer

the answer is 9.23mg confused on how they get that..

anonymous · Answer

By doing something wrong, unless you've misstated the problem.  The solubility of O2 is 1.00 mg/100g of water.  You have 200g of water.  Obviously you can dissolve no more than 2.00 mg of O2 in it.

anonymous · Answer

At 16.5° C and 1 atm, oxygen has as solubility of 1.00 mg/100g water. When air is equilibrated with a 200g sample of water at this temperature and pressure, how many milligrams of oxygen gas are dissolved? (Assume that air contains 21 mol % oxygen.)
A) 0.0462 B) 13.8 C) 2.00 D) 4.62 E) 9.23 Answer: E

This is from just googling it, says the answer is 9.23 too but the person that posted and made this test is not my teacher its some random obviously. I don't think they are both wrong if they went through the trouble of recreating a test but then again what do I know. We also didn't use the information assume 21 moles/100 moles of air but idk.

anonymous · Answer

Well, that demonstrates the limitations of google as a learning tool.  The correct answer is (C) 2.00 mg.   There is no need for the partial pressure of O2.

It would be a Henry's Law problem IF they told you the Henry's Law constant and the pressuer, and THEN asked you to calculate how much would dissolve.  Then you'd need to use the partial pressure of O2 and the Henry's Law constant to calculate the solubility, and then you'd use the solubility to calculate the amount dissolved in the saturated solution.

However, in this case, you've just been told the solubility directly, so you don't need to calculate it.

It is always possible that the question has been garbled, so that the question as correctly stated has an answer of 9.23.  I don't know.

anonymous · Answer

To hell with this problem!