Comment · Sun, February 16, 2014
Issue with Caffeine HCL Solution
Original post in this thread
MisterYouAreSoDumb · 7 points
I am not a chemist by any means, so I am a little unclear about a couple things. I am trying to make a solution of caffeine HCL by doing an acid/base reaction with anhydrous caffeine and hydrochloric acid. I am doing this to increase the solubility of caffeine in water, as this is really the only way to get it in the concentrations I need.
So I slowly add 24 grams of caffeine to 30ml of 38% hydrochloric acid. Then I add water till the solution reaches a total volume of 120ml. At that point, it clears up and forms a perfect solution with no caffeine left suspended. I checked the pH of the solution, and it is neutral at 7. At this point I figure it worked properly, since the pH is neutral. However, the solution is super sour/acidic in taste. I double checked my pH test strips in pure water and a solution of citric acid and water, and they seem to be fine. The pure water gives the same reading as my caffeine HCL solution.
So a couple questions. First, is a solution of caffeine HCL going to be stable at room temperature, and be safe to consume? Two, why is it sour if the pH is neutral?
What they were answering
AUSinUSA · 1 points
Okey dokey, was busy last night. I'm graduating in May with a biochem degree but I have a minor in chem, so I'll try and do this from a purely analytical perspective.
So the structure of caffeine is a purine with three methyl groups added to three of the four nitrogens. The molar mass is 194.19 g/mol. The molecule can arguably pick up 4 H+ ions, but the repulsion will put the pKb of the 2nd through 4th protonations too acidic for practical use. Assuming this molecule will pick up 1 mol H+ per mole caffeine, our hypothetical will dissolve 10 g:
10 g caffeine / 194.19 = 0.0515 mol caffeine
0.0515 mol caf = 0.0515 mol HCl for reaction
Molar Mass HCl = 34.46
0.0515 mol HCl * 34.46 g/mol = 1.775 g HCl
To decrease Caffeine(+)-(-)Cl ions from forming and secondary reactions, I'll dilute the HCl down to 10%
According to this chart, the density of 10% HCl 1.048 g/mL
1.775g HCl = 17.75 g 10% HCl
17.75g 10%HCl /1.048 g = 16.937 mL of 10% HCl
Add 10 g of caffeine to 16.937 mL of 10% HCl and dilute to as unsalty as you want.
Your solution has 24 g caffeine and (30ml*1.189g/mL*.38) 13.555 g HCl. 2.4x the weak base and (13.555/1.755) 7.7x the strong acid. What you have is extremely acidic and the caffeine is likely proto…
u/MisterYouAreSoDumb
Thanks for the detailed response! I will give this a shot.
And congrats on the biochem degree!