Titration the New World Way (8.2) or the old world way (7.0)?

[Denden5136]

I was given a question about whether there is a theoretical advantage of titrating the TA sample to a pH of 8.2, or using the old world method of titrating to 7.0. My thoughts are that the titration is at the equivalent point near 7.0 (weak acid/weak base), so using phenolphthalein would be a better indicator (8.2) than titrating with bromothymol blue (6.0). Probably a geeky question, but any thoughts?

 

[BarrelMonkey]

For consistency I go with the pH 8.2 standard. The difference between 7 and 8.2 really isn't much: as you'll know if you've done some of these titrations, the pH changes really fast with every additional drop of titrant once you get north of pH 6 or so. In most cases I don't think the difference between 7 and 8.2 would be actionable, meaning it wouldn't change your decisions as to how to treat your wine.

I've used phenolphthalein in the past but much prefer to go with my pH meter as the readout. The phenolphthalein color dissipates over time, so if you titrate slowly and carefully to the first hint of pink color it will go away and you can keep adding more NaOH - possibly leading to overestimation of your TA. For the phenolphthalein method to work, you have to titrate 'fast' - keep the burette flowing until you get a robust color change. It's definitely a technique that has to be learned, whereas I think the pH probe is more forgiving.