Standardizing KOH question


Help Support SoapMakingForum:


Well-Known Member
Jun 28, 2016
Reaction score
On page 171 of Dunn's SSM:

1. Add water to 3 flasks, 50ml each.
2. Add phenolphtalein, 5-6 drops, to each flask.
3. Analytically add 10.XX KOH solution/suspect lye to each flask.
4. Add 5ppt or 500ppt (for either 5ppt or 500ppt lye) citric acid solution to the flask until the pink disappears.
5. Calculate.

Have two questions:

The original procedure is for testing 5ppt lye. Do I add the same (50ml) amount when testing 500ppt lye, or should the water quantity be greater? What is the purpose of the water in the first place?

Also very intriguing - why does the color dissipate on it's own? I had to reapply phenolphtalein three times for flask 3. I applied it at the start of the procedure, to all 3 flasks, as instructed, but by the time I was done titrating flask 1, the other two had lost all the pink on their own. What gives? It is very possible that my containers are leeching acid into the 40-50% lye solution as they wait, giving me false results and pink dissappearence. They are polystyrene cups...

Edit: upon inspection of chemical resistance documents, the PS cups shouldn't be affected by such a short exposure. No idea why it de-pinked itself then.
Edit 2: tried thoroughly cleaned (distilled h2o) glass jars, same problem. The amount of phenolphtalein was increased to a rather large squirt. The very strong initial pink/purple dissipates to something only BARELY visible within a minute without the addition of any acid. This problem renders the test very hard to pull off, the likeliness of getting to within a drop accuracy, merely gauging the quantity of acid by the disappearence of a pink already barely visible is... tiny :mrgreen:

And edit 3 (solution found, hehe): my knowledge of chemistry is lacking. Many of you probably know this, but to other laymen like me: the highly alkaline liquid with phenolphtalein that is initially very purple, and should stay purple, for whatever reason goes "dormant" and loses basically all it's color. Then when you go ahead and add acid to a seemingly non-alkaline (absence of the indicator purple) liquid, it comes alive again and the purple is back. Blah :). Anyways, I've completed the test now.
Last edited: