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neeeeeem

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« on: July 24, 2018, 12:09:34 AM »
So, I made the mistake of accelerating chemistry in summer school, and now I'm stuck with these questions and I have no clue were to begin:

A flask contains 2 mol of nitrogen gas and 2 mol of helium gas. how many grams of argon must be pumped into the flask in order to make the partial pressure of argon twice that of helium?

for this question, right now I've assumed that volume is 1L (not sure if this is the way to do it) and grabbed the molar mass of helium, multiplied it by 2 mols and multiplied that by 2 to get the density (in g/L) of argon I need to get double of helium, but something tells me I'm not doing this right...

A sample gas at stp has a density of 2.16g/L. the sample is then transferred to a heating chamber at 150kPa. Its density changes to 0.72 g/L. what is the kelvin tempreature inside the chamber?

for this question, I am generally a bit clueless. I used gay lussac's law to get p1/t1 = p2/t2, which translates to 101.325kpa/273K = 150kpa/x kelvins, with x equating to 404.145k. however, I totally disregarded density, so I don't think this is the right approach either

also, thanks for your time and help. I'm desperate and this is due tomorrow.
« Last Edit: July 24, 2018, 01:01:03 AM by neeeeeem »

billnotgatez

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Re: Grade 11 Chemistry: Gasses help
« Reply #1 on: July 24, 2018, 12:47:05 AM »
You have to show your attempts or thoughts at solving the question to receive help.
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neeeeeem

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Re: Grade 11 Chemistry: Gasses help
« Reply #2 on: July 24, 2018, 01:02:23 AM »
Oops, sorry, billnotgatez, I added in my steps to solve each question in the original post. I am desparate for an answer right now, apologies for the rashness.

You got any clue what to do though? I don't think any of my approaches are right

billnotgatez

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Re: Grade 11 Chemistry: Gasses help
« Reply #3 on: July 24, 2018, 01:45:04 AM »
hint
There are alternative formulas for the ideal gas law that involve density.
Quote
ideal gas law and density
That and a little algebra may get you the answer.

neeeeeem

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Re: Grade 11 Chemistry: Gasses help
« Reply #4 on: July 24, 2018, 01:50:32 AM »
I have. In fact I have been googling for the last 4 hours. Unfortunately, google did not suffice for me.

I know about the variation of pv = dRT with d being density, but I would have to assume both pressure and temperature, which I can't do...

EDIT: screw it, it's close to 2 am here. I'm going to assume my values are at stp because I can't bare this much longer, hopefully I can apply pv = dRT somehow. thanks for the hint though.

Borek

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Re: Grade 11 Chemistry: Gasses help
« Reply #5 on: July 24, 2018, 02:42:34 AM »
No need for densities here, it is just about applying Avogadro's law and converting between moles and grams.

If you have an equimolar mixture of two gases, what can you tell about their partial pressures (no matter what the total pressure is)? Are they identical? Different?

How many moles of a third gas need to be added so that its partial pressure is twice larger than the partial pressure of any of the gases present?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

billnotgatez

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Re: Grade 11 Chemistry: Gasses help
« Reply #6 on: July 24, 2018, 02:52:55 AM »
for you second question
from the web site
https://socratic.org/questions/how-do-you-find-density-in-the-ideal-gas-law
the formula is
PM = dRT
you know the starting T and P and d
you know the ending P and d
R is a constant
Based on the way the question is asked do you think M stays the same.
If M stays the same you have all the information to compute ending T.

« Last Edit: July 24, 2018, 06:39:28 AM by billnotgatez »