I think this is Daltons Law Problem

[haribol]

Hi guys, I hope you can help me out with this seemingly simple problem. I honestly tried but I couldn't get any answer:

A 250 ml flask contains oxygen at a pressure of 150 mmHg and another flask contains 500 ml of Nitrogen at a pressure of 135 mmHg. The two flasks were then connected so that each gas filled their combined volumes. Assuming no change in temperature, what is the total pressure of gas in the final mixture?

I think this has to do with Daltons law but I don't know how to solve it.

Why wouldn't P1+P2 give me the answer?

 

[haribol]

I think I solved the problem. I believe the key to this problem is that when each of the gas enters the new volume, the pressure by each gas changes. Then taking the final pressure contributed by each gas in the new volume, I added those to give me an answer of 140mmHg.

 

[ravenprp]

Hi there,

You are correct, this is a Dalton's Law problem. Dalton's Law states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of each individual gas. In this case, you have two different gases (oxygen and nitrogen) in two different volumes (250 ml and 500 ml).

To solve this problem, you need to first find the partial pressures of each gas. This can be done by multiplying the volume of each gas by its respective pressure and then dividing by the total volume of the mixture.

For oxygen:
Partial pressure of oxygen = (250 ml / (250 ml + 500 ml)) * 150 mmHg
= (250 / 750) * 150 mmHg
= 50 mmHg

For nitrogen:
Partial pressure of nitrogen = (500 ml / (250 ml + 500 ml)) * 135 mmHg
= (500 / 750) * 135 mmHg
= 90 mmHg

Now, to find the total pressure of the mixture, you simply add the partial pressures of each gas together:
Total pressure = 50 mmHg + 90 mmHg
= 140 mmHg

So the final answer is 140 mmHg. The reason why P1+P2 didn't give you the right answer is because you need to account for the different volumes of the gases in the mixture. I hope this helps!