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Topic: Grade 12 gas problem  (Read 3142 times)

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Offline Pyroxidy

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Grade 12 gas problem
« on: September 08, 2016, 08:55:33 PM »
Alright I'm in grade 12 chemistry, and I haven't done chem in a while so this review is a bit rough for me, but anyways.
Calculate the number of moles in 25.0 L of oxygen gas at STP. If anyone could show steps, much appreciated. Not sure if I'm supposed to use stoichiometry or a formula. I just need someone to get me rolling.
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Offline Arkcon

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Re: Grade 12 gas problem
« Reply #1 on: September 08, 2016, 09:20:46 PM »
The is a formula that you will need.  Let's try to get you close to it -- what is the definition of STP?  Can you give us its units?  That may help you find the formula you need, since it will have to use those units.
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Offline jasongnome

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Re: Grade 12 gas problem
« Reply #2 on: September 08, 2016, 11:59:55 PM »
You need to remember what you were taught about Avogadro and gas volumes. You need a constant rather than a formula - one you should know by that level.
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Offline jasongnome

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Re: Grade 12 gas problem
« Reply #3 on: September 09, 2016, 01:26:55 AM »
Quote from: Arkcon on September 08, 2016, 09:20:46 PM
The is a formula that you will need.  Let's try to get you close to it -- what is the definition of STP?  Can you give us its units?  That may help you find the formula you need, since it will have to use those units.

This advice may be misleading as the full formula probably isn't required. At grade 12 I would expect them to be given a constant for STP conditions.

The problem with giving advice on this is that atm there is huge confusion over what STP actually is, IUPAC, NIST, the EPA and various different exam bodies around the world all seem to use different values.

IUPAC state that STP is 273K and 100 kPa, but the British A level curriculum (which I teach) uses, 298K (ie room temperature) and 1 atm (approx 101kPa). Some bodies use 293K.

Pyroxidy needs to use whatever his or her examining body uses, which I don't know because I don't know what country they're in or what syllabus they're studying. Of course if Pyroxidy's syllabus uses the Universal Gas Constant, then your advice stands and the whole formula is needed.

In the UK syllabus the entire equation is used in the physics A level, but in the chemistry A level, they are given the constant for the conditions of the experiment (for example at 298K and 1atm, 1 mole of gas occupies 24L)
« Last Edit: September 09, 2016, 01:48:10 AM by jasongnome »
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Offline Arkcon

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Re: Grade 12 gas problem
« Reply #4 on: September 09, 2016, 05:47:34 AM »
Your wall of text on the topic of the definition of STP is valid.  However, whatever definition of STP they've been given, will give them a hint to the Gas Laws, which was their responsibility to determine.  This board has rules for the sorts of hints we like to give, to let us know the student is at least trying.
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Offline jasongnome

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Re: Grade 12 gas problem
« Reply #5 on: September 11, 2016, 10:11:03 AM »
Quote from: Arkcon on September 09, 2016, 05:47:34 AM
Your wall of text on the topic of the definition of STP is valid.  However, whatever definition of STP they've been given, will give them a hint to the Gas Laws, which was their responsibility to determine.  This board has rules for the sorts of hints we like to give, to let us know the student is at least trying.

I have no problem with that, but if it was a British student studying A level chemistry but not physics, they won't know the gas law equation, nor be expected to, but would be expected to know how to use the constant for an ideal gas at RTP.

I merely tried to ensure it was possible for the student regardless of the curriculum they're studying.
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Offline Vidya

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Re: Grade 12 gas problem
« Reply #6 on: September 11, 2016, 11:31:14 AM »
Quote from: Pyroxidy on September 08, 2016, 08:55:33 PM
Alright I'm in grade 12 chemistry, and I haven't done chem in a while so this review is a bit rough for me, but anyways.
Calculate the number of moles in 25.0 L of oxygen gas at STP. If anyone could show steps, much appreciated. Not sure if I'm supposed to use stoichiometry or a formula. I just need someone to get me rolling.
Let me try to help you ...
Try to find out the relation between moles and  volume at STP ...
Try to understand this with the help of Avogadro's law ...
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