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I am experimenting with different levels of concentrated caffeine solution. The solution has a small percentage of ethyl alcohol, in the $\ce{H2O}$.

Problems encountered too much ethyl alcohol solidifies the powder into clumps, adding water dissolves the clumps further into smaller clumps.

What formula allows me adjust the balance of the ethyl alcohol / water / caffeine powder, so that I know what concentration I have for the caffeine for each semi-solidified solution?

My goal is to find a compromise for the highest concentration of caffeine solution for a given semi-solidified solution.

For Example:

If I add $\pu{60 mL}$ of $\ce{H2O}$ to $\pu{31,090 mg}$ of caffeine powder then add $\pu{10 mL}$ of ethyl alcohol, the powder fully absorbs all $\pu{60 mL}$ of the $\ce{H2O}$ so it becomes a solid clump. If I add another $\pu{90 mL}$ of $\ce{H2O}$ the clump turns into a solution. But, I am uncertain what concentration the solution is. I need to experiment with the semi-solidification state and concentration level. To find the highest concentration for a compromise of the semi-solidified solution state.

Reference:

if 1 gm of Caffeine dissolves in 46 mL water at room temp.

if 1 gm of Caffeine dissolves in 5.5 mL water at 80 degree C.

if 1 gm of Caffeine dissolves in 1.5 mL water boiling water.

if 1 gm of Caffeine dissolves in 66 mL alcohol at room temperature.

if 1 gm of Caffeine dissolves in 22 mL of alcohol at 60 degree C.

?1.) What is the formula for adjusting volume H2O / Ethyl Alcohol at a certain temperature, which takes into account the Caffeine grams included is always dissolved at 40 degrees C constant?

?2.) What is formula for finding the minimum amount of $\ce{H2O}$ / ethyl alcohol that fully dissolves a given amount of caffeine powder at a certain temperature, to help find the highest concentration limit for a given temperature?

For example:

If the temperature constant is 40 degree C for both H2O and Ethanol, and there is 1000 mg of Caffeine to dissolve.

What is the maximum concentration per mL of the 1000 mg at 40 degrees C, that fully dissolves caffeine? Basically what is the minimum amount of liquid volume at 40 degrees C that dissolves the Caffeine, resulting in highest concentration.

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  • $\begingroup$ You mean 31.1g of coffeine, right? $\endgroup$
    – Karl
    Commented Dec 6, 2019 at 19:22
  • $\begingroup$ The solubility of coffeine in water is 20g/l, even a bit less in ethanol (at room temperature). What you have is a suspension, not a solution $\endgroup$
    – Karl
    Commented Dec 6, 2019 at 19:25
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    $\begingroup$ There is no straightforward formula. You determine the solubility in a few alcohol/water ratios by drying and weighing the saturated solutions, and then interpolate. $\endgroup$
    – Karl
    Commented Dec 6, 2019 at 20:12
  • $\begingroup$ Yes 31.09 grams $\endgroup$
    – jesse
    Commented Dec 6, 2019 at 20:36
  • $\begingroup$ Can't I use Enthalpy? $\endgroup$
    – jesse
    Commented Dec 6, 2019 at 21:22

1 Answer 1

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A structured approach to this is to use at least five mixtures of the solvents and saturate with caffeine, stirring for at least four hours. The five mixtures are not picked arbitrarily but can be set at idealised levels. If you use 100% ethanol and water as the extremes, then you want 50:50 and two inbetween on either side. These can them be combined with your process variable if you desire, which seems to be temperature. Measure the concentrations of each and derive the equation using line of best fit (Excel and Minitab can do this). If you have JMP or Design Expert for example, you can set this up as a DOE. In either case, now you can choose your optimum.

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