7. Gases
Partial Pressure
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Here in this example question it says, a container has 16.7 grams, o 2, 8.1 grams, h 2, and 35.2 grams, n 2, and contains a total pressure of 0.83 atmospheres. We're asked to calculate the mole fraction of o 2 and its partial pressure. Alright. To determine the partial pressure of o 2, so pressure of o 2 equals the mole fraction of o 2 times the pressure total. Right now we already know what the total pressure is, it is 0.83 atmospheres. So to determine partial pressure we first have to find the mole fraction of 0 2. Remember mole fraction of o 2 will equal the moles of o 2 divided by total moles of all the together. So we're gonna take here, we're gonna say we have 16.7 grams, o 2, 8.1 grams, h 2, and 35.2 grams, n 2. We're gonna convert each one of these grams into moles. So we look on the periodic table for the atomic masses of oxygen, hydrogen, and nitrogen. Here, 1 mole of o 2, 2 oxygens comes out to 32 grams, 1 mole of h 2, 2 hydrogens when you add up their atomic masses is 2 point 016 grams, and then you have 2 nitrogens, so 1 mole of n 2 is 28.02 grams. Here all of our grams cancel out and we'll have the moles for each one of these gases or each one of these, yeah, each one of these gases. So that's gonna come out to 0.5219 moles of 024.0179 molesh2 and 1.2562 moles of n 2. So take those and plug them in. So we have 0.5 219 moles of 2. On the bottom we have the collective moles of everyone. So here we're just adding them all together. K. And then when you work that out, you'll get your mole fraction for 02, which comes out to be 0.0900. Take that mole fraction and plug it in here. So here's our mole fraction of o 2, remember mole fraction is a unitless number. So then 0.0900 times 0.83 atmospheres comes out to 0.075 atmospheres. Here our answer has 2 significant figures because our lowest number of sig figs are 8 8.1 and 0.83. They both have 2 sig figs. So just remember, utilizing Dalton's law, we can use the mole fraction of any gas times the pressure toll to find the partial pressure of that particular gas.
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