chem lab

[Botaras]

which method do you think is more accurate to determining the concentration of acetic acid in vinegar,the ph meter or the phenopthalein?

pls help me guys!!

[ChemSiddiqui]

pH meter will just tell you the pH of the solution while phenopthlein is an indicator. You can take it from here.

[DrDNA]

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.

[Botaras]

thanx for your answers

[John Cuthber]

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%

[DrDNA]

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.