Density changes of compounds when put in a mixture

  1. Hello,

    I was wondering conceptually, why does the density of the individual components change when they are added into a liquid mixture?

    So consider adding ethylene glycol and water together, when they are added to a container as a mixture, their densities are no longer their densities when they were in separate containers, why is this conceptually?
     
  2. jcsd
  3. Borek

    Staff: Mentor

    I am not sure what your question is, as I have no idea what is a "density of an individual component" in a mixture.

    Does the question translate to "Why density of the mixture is not weighted average of the densities of its components?"

    If so, answer is simple - volumes are not additive. Imagine mixing sand and marbles - as sand goes in between the marbles, final volume is not sum of volumes, but is definitely lower. Why it is not necessarily exactly the same effect at work each time (sand and marbles don't interact and don't order each other), final result is almost always identical - volume of the mixture doesn't equal sum of volumes of the components.
     
  4. So I can't calculate the density of the new solution by sum of mass/sum of volumes
     
  5. Borek

    Staff: Mentor

    No, volumes are not additive. If you mix 50 mL of ethanol and 50 mL of water you get 96.4 mL of the solution.
     
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