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  1. #11
    RobertP's Avatar
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    Heather you may not be missing anything. I may be the one missing something here. I started with distilled water room temp 50ml. I heated the water to 180 degrees. I added 13.5 grams of FO and 2 grams of edta. After mixing I ended up with over 50ml of vol. It was closer to 60ml. This is why I asked about the proper way to mix. I don't know if the increase of the vol. to around 60 ml was due to the addition of the FO and edta or the temp of the water or both. Like I said I'm no chemist. So if it is not possible to gain vol. by how I described then the only thing that could have gone wrong is my initial measuring of the H2O. Robert
    Last edited by RobertP; 01-21-2009 at 10:59 AM. Click to view previous post history.

  2. #12
    Photo Engineer's Avatar
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    Robert;

    Probably both! What you had was about a 22.5% solution due to the error in starting with 50 ml of water and ending with 60 ml. When you add a solid to a liquid to make a solution, volume can increase or decrease.

    PE

  3. #13
    RobertP's Avatar
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    Thanks PE, I understand now. That's what I suspected. Robert

  4. #14

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    Quote Originally Posted by Photo Engineer View Post
    When you add a solid to a liquid to make a solution, volume can increase or decrease.

    PE
    I understand that the volume of [liquid A + solid B] may be less than the sum of the uncombined volumes... but how can the volume of [liquid A + solid B] become less than the volume of liquid A, in the absence of a reaction between A and B that reduces intra ? and or inter-molecular distances?

    It is intuitive that the combination of the two volumes might be additive.

    It is even understandable that on occasion, the volume may remain unchanged
    (if for example "empty" space were somehow present)

    But,

    Can someone explain how the combination of 2 volumes can result in a lower TOTAL volume?

    A common example would be helpful too.

    Thanks
    Last edited by Ray Rogers; 01-21-2009 at 06:21 PM. Click to view previous post history.

  5. #15
    Photo Engineer's Avatar
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    Addition of Silver Nitrate to water can decrease volume, thereby increasing density.

    Addition of Ammonia gas to water can increase volume thereby decreasing density.

    So, 100 ml of 1 N AgNO3 is higher in weight than 100 grams, but 100 ml of 28% Ammonium Hydroxide is lower in weight than 100 grams. Just two for starters.

    PE

  6. #16

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    [QUOTE=Photo Engineer;739455]Addition of Silver Nitrate to water can decrease volume, thereby increasing density.
    QUOTE]

    Yes.

    You gave 2 examples, but I only am really concerned with the first case.

    It is interesting in fact that you mention the case of silver nitrate; I was introduced to this phenomenon years ago by a researcher who was showing me his emulsion lab... he posed the question to me if I knew the explanation... he was always curious to find that after a few hours he would return to the lab to find the volume of silver nitrate (prepared in a volumetric flask) was always lower than upon inital mixing... not having been there during mixing, I could only make a wild guess or two, but it was claimed to be a real difference presumably not related to evaporation nor temperature or pressure changes.

    My question is- What is the explanation for this behaviour?

  7. #17
    Photo Engineer's Avatar
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    Among other things, ionization may increase or attractive forces may increase, decreasing molecular bond distance and so volume may decrease. There are a variety of reasons. Look up van der Walls force among others.

    PE

  8. #18

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    "... how can the volume of [liquid A + solid B] become less than the volume of liquid A, in the absence of a reaction between A and B that reduces intra ? and or inter-molecular distances?"

    Quote Originally Posted by Photo Engineer View Post
    Among other things, ionization may increase or attractive forces may increase, decreasing molecular bond distance and so volume may decrease. There are a variety of reasons. Look up van der Walls force among others.

    PE
    Thanks.

    I imagine I won't be able to discover much by myself... but I will try.

    I welcome contributions from others who have some insight on this
    (to me at least) curious behaviour.
    I am particularly interested in what is unique about AgNO3 in this respect.

    TIA

    Ray

  9. #19
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    Ray, the same thing is observed with most inorganic salts as well as Silver Nitrate. I used that as an example only as it is familiar to most of us.

    PE

  10. #20

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    Quote Originally Posted by Photo Engineer View Post
    Ray, the same thing is observed with most inorganic salts as well as Silver Nitrate. I used that as an example only as it is familiar to most of us.

    PE
    OK.

    But the question still remains as to how and why the molecular bond lengths / inter molecular distances change...
    specifically, Why do they shrink in one case and grow in another?

    (Perhaps it is a very simple explanation after all;I often overlook Van der Walls and Hydrogen bonding so it shouldn't be hard to imagine.)

    I am curious, have you noticed this to be "instant", or can you confirm a time component is involved?

    Ray
    Last edited by Ray Rogers; 01-21-2009 at 08:30 PM. Click to view previous post history.

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