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A question about solutions...

  1. Mar 10, 2017 #1
    Okay...In most of the solutions(I am talking about polar-in-polar solutions) , the solute becomes ions and these ions are surrounded by solvent molecules...A solution is a type of mixture, so its constituents retain their own properties...My question is that how, after the dissolution of solute into ions, can it retain its original properties???...
     
  2. jcsd
  3. Mar 10, 2017 #2

    Borek

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    Staff: Mentor

    In a very broad sense. But in general - no.

    They don't.
     
  4. Mar 10, 2017 #3
    The word "mixture" is used in different ways, which may be confusing. A physical mixture of two substances comprises two distinct phases, however finely divided and intimately dispersed they may be. (Phase: “A state of matter that is uniform throughout, not only in chemical composition, but also in physical state”). At the molecular level, the substances are not mixed; A molecules are surrounded by A molecules, and B molecules by B molecules (except for the interfaces, which comprise a tiny fraction of all the molecules). This is the only kind of mixture where the constituents retain their own properties. (Within their own phases, that is; a fine mixture of two substances may in bulk have an average property such as density.)

    In a solution the substances are mixed intimately at the molecular level; A molecules are surrounded by both A and B molecules, and likewise for B molecules. A solution comprises a single phase. Its physical properties (e.g. density) are those of the solution; the properties of the individual components are not retained (there is no portion of the solution, however small, that has the density of pure A). However, to confuse things, we sometimes use the word "mixture" about a solution. We might talk, for example, of a 1% solution of ethanol in water, but if we mixed them in a 50:50 ratio we might refer to it as a "mixture" of ethanol and water (perhaps from the irrelevant difficulty of deciding which was the "solvent" and which the "solute"). And we describe two substances as "miscible" if they form a solution (i.e. they are miscible at the molecular level), and "immiscible" if they phase-separate and form a physical mixture. In particular, we are likely to refer to a "solution" of gases as a mixture.

    In addition, forming a solution may involve chemical change, such as ionisation. In this case we usually call it a solution; we generally keep the word "mixture" for solutions where the components are not chemically changed.

    Note that in a solution some of the constituent properties may be retained; e.g. A may be chemically reactive towards C both in the pure state and in solution, or it may absorb light at a given frequency both pure and in solution. But only in a physical mixture does it retain all its properties. And when we talk about a mixture in that way, I think it is usually to distinguish a physical mixture from a compound (e.g. a mixture of iron and sulfur from iron sulfide), not from a solution, which is neither a mixture nor a compound in that sense.
     
  5. Mar 10, 2017 #4
    So are you asking, for an example, how NaCl dissolved in water would retain its properties from when it was in solid form?
     
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