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Thread: What's the basic difference of molarity,molality,normality

  1. #1 What's the basic difference of molarity,molality,normality 
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    what is the basic difference between molarity,molality and normality? Why we say that its molality or noramality or molarity???


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    Forum Sophomore Matt Lacey's Avatar
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    Molarity - mol/dm³ (moles per solvent volume)

    Molality - mol/kg (moles per solvent mass)

    Normality - blah, can't think of how to best describe it. It to do with ions dissociating... eg if you have iron(III) nitrate solution, Fe(NO3)3, you make up a 1 M solution of that, and the ions dissociate, you have 3 nitrate anions for each iron, therefore the solution is 3 Normal in nitrate... geddit?


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    Quote Originally Posted by Matt Lacey
    Molarity - mol/dm³ (moles per solvent volume)

    Molality - mol/kg (moles per solvent mass)

    Normality - blah, can't think of how to best describe it. It to do with ions dissociating... eg if you have iron(III) nitrate solution,Fe(NO3)3 , you make up a 1 M solution of that, and the ions dissociate, you have 3 nitrate anions for each iron, therefore the solution is 3 Normal in nitrate... geddit?
    so that means that the amount of anions in a 1M solution tells you its normaility? 3? is that the same for (NaNO3)? it has 3 normal nitrate in it?
    its the same right? even without the (III)
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    Forum Sophomore Matt Lacey's Avatar
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    No, sodium nitrate would be 1 N in nitrate - 1 mole of sodium nitrate dissociates to give you 1 mole of solvated nitrate - in the case of Fe(NO3)3, it 1 mole dissociates to give 3 moles of solvated nitrate effectively because there are 3 nitrates per Fe ion.
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    Forum Freshman Keith's Avatar
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    Quote Originally Posted by Matt Lacey
    Molarity - mol/dm³ (moles per solvent volume)

    Molality - mol/kg (moles per solvent mass)

    Normality - blah, can't think of how to best describe it. It to do with ions dissociating... eg if you have iron(III) nitrate solution, Fe(NO3)3, you make up a 1 M solution of that, and the ions dissociate, you have 3 nitrate anions for each iron, therefore the solution is 3 Normal in nitrate... geddit?
    Actually, Molarity - mol/dm³ (moles of solute per solution volume)

    Molality - mol/kg (moles solute per solvent mass)

    Normality from wiki Definition:
    A normal is one gram equivalent of a solute per liter of solution. The definition of a gram equivalent varies depending on the type of chemical reaction that is discussed - it can refer to acids, bases, redox species, and ions that will precipitate.

    Just correcting and elaborating.


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    Quote Originally Posted by Matt Lacey
    No, sodium nitrate would be 1 N in nitrate - 1 mole of sodium nitrate dissociates to give you 1 mole of solvated nitrate - in the case of Fe(NO3)3, it 1 mole dissociates to give 3 moles of solvated nitrate effectively because there are 3 nitrates per Fe ion.
    ok so theres 3 moles of nitrate dissociating with the Fe because there is 3 Fe in the molecule? giving it a 3 normalcy
    and one in the Sodium nitrate because theres 1 sodium, giving it a one?

    does that make sense?
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    Forum Sophomore Matt Lacey's Avatar
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    Nope - 3 nitrate per Fe, not 3 Fe

    Fe(NO<sub>3</sub>)<sub>3</sub>(s) --> Fe<sup>3+</sup>(aq) + 3 NO<sub>3</sub><sup>-</sup>(aq) => 3 Normal
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    cool thanks
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