Partial Pressure Example 2

Jules Bruno
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if 12 g of helium and 20 g of oxygen are placed inside a five liter of cylinder at 30 degrees Celsius, what is the partial pressure of the helium gas? All right, so they're giving us information on two gas. Is there giving us information on helium and oxygen, but realize they're only asking for information in terms of partial pressure for the helium. With the healing I have, it's grams. And from that I can determine its moles. I have the volume of the container and I have the temperature of the container. With this information, I can find the partial pressure of helium gas by utilizing the ideal gas law. So we're gonna say here pressure of helium equals moles of helium. Times are times t divided by V. We don't even need to look at the grands of oxygen because the question again is only asking about the partial pressure of helium. All right, so let's take the 12 g of helium We look on the periodic table, you'll see that the atomic massive helium is approximately 4. grands helium for everyone. More of helium grams Here, cancel out and I'll have my moles as 2. Moles of helium. So take that. Plug it into the formula. So 2.9978 moles off helium multiplied by my gas law on my gas. Constant 0.8 to 06 leaders times atmospheres over moles Times K Remember, temperature must be in Kelvin. So the 30 degrees Celsius I'm gonna add to 73. to it and that gives me 303. 15 Kelvin. Then we take the volume, which is five leaders, and we just plug it in. Look at the units leaders cancel with leaders. Kelvin's cancel out with Calvin's moles cancel with moles And at the end, what we have left is atmospheres. So we plugged that in and we'll get 14.9149 atmospheres If we look at the sig Figs within our question, we have three sig figs, three sig figs to sig figs and one sigfig here. If we wanted 16 figure around down to 10 atmospheres again, that's such a big deviation from our actual number. So let's go with a number that makes more sense because we don't want around so much we're gonna say our answer here is 14.9 atmospheres again. We're constantly trying toe Remember, significant figures play a role in a lot of our questions here. We're not being asked to directly, but when applicable, we should apply it here. It wouldn't make sense to apply it because it would round our answer toe a number that doesn't quite fit. Going from 14.9 to 10 is such a big difference. So here we're just gonna go with 366 14.9 atmospheres is more reasonable. It's not a big deviation from our original answer. So just remember, if we have the moles, the temperature and the volume, we confined the partial pressure of a gas by using the ideal gas law formula.