March 06, 2021, 09:13:48 AM
Forum Rules: Read This Before Posting


Topic: Oxygen and hydrogen: i need help on my pre laboratory exercise...  (Read 16609 times)

0 Members and 1 Guest are viewing this topic.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26313
  • Mole Snacks: +1711/-402
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Oxygen and hydrogen: i need help on my pre laboratory exercise...
« Reply #15 on: August 31, 2006, 01:14:22 PM »
Well I forgot to mention the percentage amounts to take into consideration.

Exactly :)

Quote
We aren't adding 1 L, we're assuming densities at STP, which is 22.44 L.  So the volume is 22.41, not 1.

That was just an example.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline english

  • Chemist
  • Full Member
  • *
  • Posts: 535
  • Mole Snacks: +31/-10
  • Gender: Male
  • grad student
Re: Oxygen and hydrogen: i need help on my pre laboratory exercise...
« Reply #16 on: August 31, 2006, 01:21:45 PM »
Yeah sorry for the mistake, I just get a little imaginative sometimes  ;D

I know it was just an example when you said 1 L, just trying to make you angry  ::)

Offline Will

  • Organic Dude
  • Chemist
  • Full Member
  • *
  • Posts: 400
  • Mole Snacks: +58/-2
  • Gender: Male
Re: Oxygen and hydrogen: i need help on my pre laboratory exercise...
« Reply #17 on: August 31, 2006, 01:26:17 PM »
Well I forgot to mention the percentage amounts to take into consideration.  In this case we know there is more oxygen, which is 32.00 g/mol, and nitrogen molar mass plus oxygen molar mass is obviously greater.

It doesn't actually matter what percentage it is. As soon as you know air is a mixture of oxygen (Mr=32) and other gases with Mrs less than 32 then the density of air must be lower than that for oxygen. It wouldn't matter if air was 99.99% O2 or 0.01% O2 the density of air would still be lower. Obviously gases like Ar and CO2 raise the density but that is negligible compared to N2.

We aren't adding 1 L, we're assuming densities at STP, which is 22.44 L.  So the volume is 22.41, not 1.

That was just an example.

And a perfectly legitimate example. The question told you that 1 mole of gas occupies x litres, when you are working with density it doesn't matter how much gas you have the density will be the same, you could have assumed there to be 100 billion litres of gas or 0.00001 moles of gas it won't make a difference.

Yeah sorry for the mistake, I just get a little imaginative sometimes ;D

I know it was just an example when you said 1 L, just trying to make you angry ::)

LOL ;D

Offline english

  • Chemist
  • Full Member
  • *
  • Posts: 535
  • Mole Snacks: +31/-10
  • Gender: Male
  • grad student
Re: Oxygen and hydrogen: i need help on my pre laboratory exercise...
« Reply #18 on: August 31, 2006, 01:41:36 PM »
Quote
then the density of air must be lower than that for oxygen

You mean higher?

Offline Will

  • Organic Dude
  • Chemist
  • Full Member
  • *
  • Posts: 400
  • Mole Snacks: +58/-2
  • Gender: Male
Re: Oxygen and hydrogen: i need help on my pre laboratory exercise...
« Reply #19 on: August 31, 2006, 01:42:12 PM »
Quote
then the density of air must be lower than that for oxygen

You mean higher?

No I mean lower. :P

Offline english

  • Chemist
  • Full Member
  • *
  • Posts: 535
  • Mole Snacks: +31/-10
  • Gender: Male
  • grad student
Re: Oxygen and hydrogen: i need help on my pre laboratory exercise...
« Reply #20 on: August 31, 2006, 02:17:44 PM »
Of course.  I have this nasty habit of not really reading the question closely. 

20% oxygen, 80% nitrogen.

Sheesh... :-X

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26313
  • Mole Snacks: +1711/-402
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Oxygen and hydrogen: i need help on my pre laboratory exercise...
« Reply #21 on: August 31, 2006, 02:43:23 PM »
I know it was just an example when you said 1 L, just trying to make you angry  ::)

Not an easy task but doable. Don't try too hard ;)
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Sponsored Links