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A 'good' pH meter is generally more accurate than determining pH with phenopthalein and your eyeball.


That said, accuracy can be 'greatly' improved if you use a good UV/vis to monitor the color change with phenopthalein.


So the answer is: it depends on how good your pH meter is vs how you are reading the phenopthalein.


With either one, you will greatly increase accuracy by doing a titration.

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Since phenolphthalein is colourless in netural solutions and colourless in acid solutions I can't see how you could use it (and only it) to measure the strength of an acid like vinegar.

You could use it as the indicator in a titration to get much better accuracy than a pH meter will give you.

Even with the sort of equipment I used at school a titration could tell if the vinegar was 5% or 5.05% With practice and good experimental design you should be able to distinguish 5% from 5.01%

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That's a good point and I forgot that it is colorless in neutral to acid solutions.

It is pink to purple basic solutions.....which doesn't do you much good 'except' as JC mentioned above..........


Conclusion: You should have more than enough info to answer your homework question.

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