Titration Indicators (1 Viewer)

[scardizzle]

Hey BOS, this may sounds like a stupid question but in what circumstances would i not use phenolphthalein as my indicator in a titration?

According to wiki: An acid-base titration is the determination of the concentration of an acid or base by exactly neutralizing the acid/base with an acid or base of known concentration.

In that case wont the pH we're looking for always be 7? So in what circumstances would I need to use something like bromethyl blue etc. ?

Any input is appreciated.

 

[MetroMattums]

When it's a weak-acid/base titration - in which case the pH would be over 7, or when it's a acid/weak-base titration - in which the case would be under 7.

If it's a weak-acid/weak-base titration there is no equivalence point because not enough acid is neutralised by the base

 

[nawor_]

the salt formed from the neutralisation may be acidic/basic/neutral which effects the resultant pH

 

[MetroMattums]

the salt formed from the neutralisation may be acidic/basic/neutral which effects the resultant pH

wtf?

Salt isn't formed from neutralisation, it's formed from an acid reacting with a metal..

 

[nawor_]

acid + base = salt + water

 

[MetroMattums]

acid + base = salt + water

ma bad

 

[iMAN2]

A weak acid + weak base are never used in a titration because they are constantly ionising and trying to reach equilibrium

 

[nat_doc]

A weak acid + weak base are never used in a titration because they are constantly ionising and trying to reach equilibrium

this means that there is no definitive "end point" and you cannot use indicators/ titration to find out its concentration.