How can I fix endpoint readings in home titration with phenolphthalein?

[Isabella74]

I was trying to do a simple titration at home to find the concentration of an acetic acid solution using sodium hydroxide, but my endpoint color change from phenolphthalein was really inconsistent between trials. I'm not sure if my technique for reading the burette is off, or if there's something about my indicator preparation I'm missing.

[James.R]

I've done a few of these with acetic acid and NaOH. The endpoint would drift from run to run even when I thought I mixed well. I found parallax was a big culprit—reading the bottom of the meniscus at eye level matters a lot. Also the pink color change in the indicator in this region can be pretty subtle, so a small mixing lag or a gentle swirl after each drop mattered. I learned to watch the color change at the bottom of the meniscus and to wait a beat after each drop, but it still felt fuzzy.

[MiaH]

Could the problem be that the NaOH bottle or standardization is off, or that the indicator stock is old? I once used a bottle that had been opened for months and it seemed to fade in the pink, which made the endpoint look inconsistent.

[Joseph92]

Another thought: for weak acid strong base titrations the equivalence point sits above 7, so the indicator range can be a little off from the true end. The color cue can be late or early depending on concentration and temperature, and that’s part of the fuzz you’re seeing rather than a clean break.

[Jonathan_S]

On a different attempt I tried a rough pH check alongside the titration and realized the jump near the end was small, so the pink lingered or vanished unpredictably. I didn't trust the molarity after that and just treated it as a rough estimate.