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Thread: Moles?

  1. #1 Moles? 
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    im taking chemisrty right now, and we've gone over Moles.
    im just a little confused though. (and my teacher isnt handy )

    if 1 mole = 22.4L
    and 1 mole = formula mass
    and 1 mole = 6.02X10^23

    then why doesnt 22.4L = 6.02X10^23?
    at least im pretty sure i heard my teacher say that they dont equal.
    anyway, i just finished trigonometry and im pretty sure if A=B and B=C then A=C......


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  3. #2  
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    Avagadrio's constant refers to the number of particles in a mole.

    So in 22.4 litres of a gas, there will be 6.02x10^23 molecules.

    22.4 litres is at 273K/0C, I assume?
    I normally use 293K or 20C, where it is 24 litres.

    so, 1 mole of H2 gas will occupy 22.4 litres, will weigh 2 grams, and will contain 6.02x10^23 molecules of H2.


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  4. #3  
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    so, 1 mole of H2 gas will occupy 22.4 litres, will weigh 2 grams, and will contain 6.02x10^23 molecules of H2.
    ok i get that now, but H2 being a gas, doesnt it expand to fill any container it is contained in, having no specific volume? so under different pressures, couldnt 500L of H2 still only contain 6.02X10^23 moleculesand still weigh 2 grams?

    (and just an after thought i had, i'd have to drink 7.5, 3 liter bottles of soda to drink a mole of soda..... or does that only apply to gasses? cause im fairly sure that deffinatly wont weigh formula mass, nor be 6.02X10^23 molecules....)
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    ok i get that now, but H2 being a gas, doesnt it expand to fill any container it is contained in, having no specific volume? so under different pressures, couldnt 500L of H2 still only contain 6.02X10^23 moleculesand still weigh 2 grams?

    (and just an after thought i had, i'd have to drink 7.5, 3 liter bottles of soda to drink a mole of soda..... or does that only apply to gasses? cause im fairly sure that deffinatly wont weigh formula mass, nor be 6.02X10^23 molecules....)
    you're question on 500L of H2... seems to be a misunderstanding.

    6.023*10^23 molecules of H2 will always weigh 2 grams. or have a mass of 2g the weight will depend on location.

    the next part when you say gases have no specific volume is untrue, are you familiar with the ideal gas law?

    pV = nRT

    if you look at this equation of state. it is clear that if you have 6.023*10^23 (1 mole) of H2 and the volume is 500L then there exist an infinite number of different pressures. The pressure will only be fixed if you specify a temperature aswell.

    (in reality the ideal gas equation of state is not accurate at high pressures but you get the point)
    everything is mathematical.
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  6. #5  
    Forum Senior Booms's Avatar
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    hmm it sounds like you've partially heard you teacher, or they've not explained clearly




    1mole of any gassous element at room temperature and pressure will fill up 22.4 cubic meters of space


    1mole is 6.02x10^23 atoms, so 1mole of hydrogen or of titanium or of potassium is always going to be 6.02x10^23 atoms, the number is reffered to as Avogadro's constant and has changed several times since it's discovery as measurements get more accurate


    1 mole of any element will weigh it's relative formula mass, hydrogen RAM is 1.01 so 1 mole of hydrogen will weigh 1.01 grams, Francium has a relative atomic mass of 223 and so 1 mole of francium will weigh 223 grams






    Quote Originally Posted by slayer-72
    ok i get that now, but H2 being a gas, doesnt it expand to fill any container it is contained in, having no specific volume? so under different pressures, couldnt 500L of H2 still only contain 6.02X10^23 moleculesand still weigh 2 grams?

    (and just an after thought i had, i'd have to drink 7.5, 3 liter bottles of soda to drink a mole of soda..... or does that only apply to gasses? cause im fairly sure that deffinatly wont weigh formula mass, nor be 6.02X10^23 molecules....)
    the 6.02x10^23 refers to mass instead of volume, 6.02x10^23 atoms of hydrogen will always weigh 1.01 grams no matter what, 500 cubic meters of H at room temp and pressure will weigh around 27.07grams
    everything has a specific volume, gasses tend to have large volumes and additionally diffuse into the surrounding's appearing to have an infinite volume potential, at room temperature (20 degrees I think) and 1 atmosphere of pressure (earth) 1 mole of gas will fill 22.4 cubic meters, under different pressures and temperatures it's true a gas could be made to fill different volumes but it would still weigh the same, density and mass are not related

    your soda idea is waaay out, the molar volume of gas applies to any element, but only as a gas and more importantly the formula mass is based on to total elements not just one, H2 is 2 atoms of hydrogen so the RAM is 2.02 and a mole of H2 wieghs 2.02 grams, Soda water has the chemical equation H2CO3 so its RAM is 62.03 (1.01+1.01+12.01+16+16+16) so a mole of soda water will weigh 62.03 grams
    Now this seems silly considering a mole is 6.02x10^23 atoms but atoms are tiny, in contrast 6.02x10^23 grains of sand would cover the united kingdoms to a depth of 100 miles 6.02x10^23 is 602,000,000,000,000,000,000,000 (602 sextillion thats 602000 trillion)
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  7. #6  
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    Quote Originally Posted by Booms
    6.02x10^23 atoms of hydrogen will always weigh 1.01 grams no matter what, 500 cubic meters of H at room temp and pressure will weigh around 27.07grams
    Quote Originally Posted by Booms
    at room temperature (20 degrees I think) and 1 atmosphere of pressure (earth) 1 mole of gas will fill 22.4 cubic meters
    Just a small nit-pick...

    It's 22.4 dm, not m. A cubic metre is 1000 times larger than a cubic decimetre, or litre.

    Also, gases occupy 22.4 dm at 0 degrees C, and 24dm at 20 degrees C. standard conditions vary.
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  8. #7  
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    Quote Originally Posted by organic god
    ok i get that now, but H2 being a gas, doesnt it expand to fill any container it is contained in, having no specific volume? so under different pressures, couldnt 500L of H2 still only contain 6.02X10^23 moleculesand still weigh 2 grams?

    (and just an after thought i had, i'd have to drink 7.5, 3 liter bottles of soda to drink a mole of soda..... or does that only apply to gasses? cause im fairly sure that deffinatly wont weigh formula mass, nor be 6.02X10^23 molecules....)
    you're question on 500L of H2... seems to be a misunderstanding.

    6.023*10^23 molecules of H2 will always weigh 2 grams. or have a mass of 2g the weight will depend on location.

    the next part when you say gases have no specific volume is untrue, are you familiar with the ideal gas law?

    pV = nRT

    if you look at this equation of state. it is clear that if you have 6.023*10^23 (1 mole) of H2 and the volume is 500L then there exist an infinite number of different pressures. The pressure will only be fixed if you specify a temperature aswell.

    (in reality the ideal gas equation of state is not accurate at high pressures but you get the point)
    oh ok, there has to be a specified tempature as well.


    but only as a gas
    lol yeah thats what i thought.


    ok thanks a lot every one
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  9. #8  
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    STP standard temperature and pressure, I think those are the only factors, at least in this case
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  10. #9  
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    gibbs phase rule will tell you that for a single phase pure component the substance can be fully defined using two state properties
    everything is mathematical.
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