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The Question sounds stupid but i have a legit problem

I mixed 1000 mL coconut water and 225 g of agar-agar to make a coconut water [CW] agar. It gave me more than 1000 ml. the medium went beyond the 1000 ml mark. the CW agar was also too soft to use

then i tried mixing 775 mL coconut water and 225 g agar-agar it gave me little below the 1000 mL mark. the CW agar was just right not too soft and not to hard :|

(I did heat after mixing during those two trials but the volume remained the same after cooling to room temp.)

Seems to break rules taught to us. i though when you add mass to a liquid it won't increase the volume but the density will increase or does this only apply to water?

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    $\begingroup$ You "understanding" of "the rule" is wrong. In general if 100 ml of a solution is needed then the solute should be dissolved in some water and then diluted to 100 ml final volume. Even mixing 50 ml of ethanol with 50 ml of water doesn't yield exactly 100 ml of solution. $\endgroup$
    – MaxW
    Feb 10, 2016 at 18:02
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    $\begingroup$ so any principles explaing why this happen? i searched everywhere in the net and all of it are about water and some other chemicals mix with it. Even my teachers can't give answers $\endgroup$
    – CheMaxtry
    Feb 10, 2016 at 18:14
  • $\begingroup$ en.wikipedia.org/wiki/Partial_molar_property Read this. $\endgroup$
    – Koba
    Feb 10, 2016 at 18:24
  • $\begingroup$ I tested using water and agar -agar the volume didn't change at all or there was no noticeable change. i did it at a small scale though. i added 25 g of agar- agar to 75 ml water but the volume remained the same while doing it to coconut water the volume increase. The Link kinda help but still trying to get a grasp on it might read more about it thanks for the reply. $\endgroup$
    – CheMaxtry
    Feb 10, 2016 at 18:30

1 Answer 1

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"The rule" is that an ideal mixture will have the volume of the sum of its components and the density will be the molar averaged density of the components. Real mixtures deviate from this rule to varying degrees.

The name of the property you're looking for that describes this deviation is "excess volume". Excess volume can be either positive (1L of A and 1L of B creates >2L of AB mixture) or negative (1L of C and 1L of D creates <2L of CD mixture). The deviation from the rule depends mostly on how the molecules of the components interact with themselves compared to with the each other. Without knowing much about this specific case, I would guess that the big agar polymer molecules interrupt the local organization of the water molecules. This causes the density to decrease.

For many fluids, such as ethanol and water, the densities have been well studied and you can look up tables of excess volume. On a quick google search, it doesn't appear that anyone has ever done this for coconut water and agar. Unfortunately, that means more work for you. Fortunately, it means you get to break new scientific ground!

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  • $\begingroup$ thank you! that cleared up things i can finally rest in peace XD $\endgroup$
    – CheMaxtry
    Feb 10, 2016 at 19:35

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