Fyndium
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Displacement?
When solids and gases are dissolved in liquids, the volume can remain the same, or even decrease at some instances, but most apparently it does never
seem to equal the actual displacement of the solid. For example, when filling a 1L flask up to 700mL with all liquid reagents, and adding 200g of
solid over reaction, the volume will not top 900mL but pretty much remain the same.
But when liquids are mixed to form a solution, will the displacement always be volumetric or will they dissolve into each other in a similar manner?
Is there any rule or formula to determine the volumes different reactants displace, or is it always case sensitive?
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Maurice-VD-3
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There is no formula. When 50 mL water is added to 50 mL ethanol, the observed volume is 96 mL. It looks as if water were made of tjyny molecules tat
are mixed to big and cumbersome ethanol molecules. The tiny water molecules can infiltrate the ethanol. And the mixture is not so cumbersome as the
sum of the two constituents.
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j_sum1
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There may be more nuance to the situation than i understand, but I always thought it was a fairly simple principle: particle packing.
A system with two different sized particles can pack more densely than a system with one particle size. In the extreme case where ine partcile is
very much smaller than the other, it can fit in the interstices between the large particles and can therefore be added up to a certain proportion with
negligible volume change. But even with very similar sized particles, there is some volume contraction on mixing.
I am not aware of any examples were mixing two liquids or dissolving a solid in a liquid results in a volume increase. Nor can I conceive of a
mechanism by which this would happen.
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Bedlasky
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Quote: Originally posted by j_sum1  |
I am not aware of any examples were mixing two liquids or dissolving a solid in a liquid results in a volume increase. Nor can I conceive of a
mechanism by which this would happen. |
Whan you dissolve some NaCl in water, volume will increase. Pretty much dissolving any ionic salt cause increase of volume of solution.
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Fyndium
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Someone explicitly stated that dissolving sodium chloride will cause the solution to actually decrease in volume. Funny how the very basic things
remain a cause of debate.
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j_sum1
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Not disagreeing. But that is not what I was trying to say.
100mL of solute - 900mL of solvent will mix up to less than one litre.
Try this. Pop a stir bar in a volumetric flask. (I know this ruins the measurement.) Then dump a salt in. Then fill to the line with water. Now, stir
to dissolve. The volume will drop.
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