titration q (1 Viewer)

[+:: $i[Q]u3 ::+]

what's the difference between equivalence point and end point?
and when u titrate, do u look for an indicator that suits the equivalence point or end point? thanks all..

 

[abdooooo!!!]

the point when the reaction is complete is called the equivalence point.

the point that the indicator changes colour is the end point.

when you titrate you choose the indicator with the end point that is as close to the actual equivalence point as possible.

does that make sense to you?

 

[+:: $i[Q]u3 ::+]

yep~! thank you =)

 

[FLR-IT]

Originally posted by abdooooo!!!
the point when the reaction is complete is called the equivalence point.

the point that the indicator changes colour is the end point.

when you titrate you choose the indicator with the end point that is as close to the actual equivalence point as possible.

does that make sense to you?

no i dont get it!!


doesnt it just change color when the reaction is complete??

since u r choosing a indicator close to the equivalence pnt it should change colour right away shouldnt it?

 

[abdooooo!!!]

Originally posted by FLR-IT
no i dont get it!!


doesnt it just change color when the reaction is complete??

since u r choosing a indicator close to the equivalence pnt it should change colour right away shouldnt it?

which part didn't you get?

end point is the pH point at which the indicator changes colour (the pH range of the indicator), but equivalence point is the pH at which both chemicals have all been used up which could differ from the pH range of indicator.

the reason for equivalence point having a pH other than 7 (neutral) is because of the salts produced during the neutralision process.

 

[Constip8edSkunk]

you are basically saying the same thing. if the equivalence pt lies in the pH range in which the indicator changes colour the titration process would be valid as the end point of titration corresponds with the equivalence point of the neutralisation reaction. however say methyl orange was chosen as the indicator for a titrating CH3COOH against NaOH, this would not b the case as the end point doesnt correspond with the equivalence pt


edit: meant for FLR-IT

 

[inasero]

you are basically saying the same thing

haha not really...endpoint and equivalence point are TOTALLY different concepts and not to be confused...

as has been stated before; endpt=where indicator changes colour
equiv pt=where there exist equal numbers of acidic and basic species in solution

in titrations specific indicators are selected so their endpoint corresponds to the equivalence point of the reaciton. So say you were titrating NaOH against HCl...at the equivalence point the pH is exactly 7 because the salt does not undergo hydrolysis and is neutral in nature...therefore we choose an indicator whose endpoint corresponds to a pH of 7...say bromothymol blue or litmus (altho pheno is commonly used because the colour change is significantly more marked).

Now I know many of you might be scratching your heads and asking- "but isnt pheno supposed to be used for titrations involving stong bases and weak acids?!" Yes you are technically correct, but it is important to keep in mind that the pH change at the equivalence pt of this reaction is very great and so even though pheno does change colour when the solution is basic, this will overall have little impact on the value of the analyte we derive for the tiration, and in the end the little error due to the slightly basic endpoint more than offsets the great error due to ambiguity in determining the endpoints of other indicators. Colour change in phenolphthalien is marked.

 

[Constip8edSkunk]

read my post again cuz u neva seems to listen 2 what i say

i was refering to what those 2 ppl were saying not end point and equivalence point

 

[inasero]

yeah you're right but i'm just saying that your first sentence is misleading...because it is not always the case...

must be the pre-HSC syndrome getting to you eh john?
don't worry we all feel it~

 

[shadowRRL]

after reading all of ur posts i still dont get a thing on wat is going on?

I thought u only have to be able to write up an experiment for titration and that was it.

Or did I miss a dot point?

 

[+:: $i[Q]u3 ::+]

you have to be able to choose a suitable indicator for your titration - one which has an end point that correlates with the equivalence point of the reaction.. am i right?

 

[d00d]

yep

 

[iambored]

i always thought they were the same thing

Originally posted by +:: $i[Q]u3 ::+
you have to be able to choose a suitable indicator for your titration - one which has an end point that correlates with the equivalence point of the reaction.. am i right?

yeah

so, in a sense they should be the same thing because they should correspond? is that right? otherwise what is the point of titrating?

 

[+:: $i[Q]u3 ::+]

exactly. i jus needed to know which was which.

 

[Dangar]

do we need to memorise the end points of all the different indicators?

 

[+:: $i[Q]u3 ::+]

jus know which indicators are used for each different type of titration
strong base/weak acid - phenolphthalein
s acid/wbase - methyl orange
w/w or s/s - bromo blue
and what kinda colour changes occur.

 

[ND]

Originally posted by Dangar
do we need to memorise the end points of all the different indicators?

Yeh there's a dotpoint saying "gather information about the colour ranges of a range of indicators", but as sique said, we only really need to know bromothymol blue, phenolphthailein, methyl orange and litmus.

 

[Constip8edSkunk]

i thought coz of the large pH change associated with s/s titration, methyl orange, phenolphthalein could also b used... also u cant titrate w/w (u can but u really shouldnt as the ph change is far from being distinct)

 

[+:: $i[Q]u3 ::+]

good point.
but then again.. we titrated vinegar wit naoh in class to find the conc. of acetic acid in original indiluted vinegar - a bit dodge when u consider ch3cooh only partially ionises.

 

[ND]

Originally posted by Constip8edSkunk
i thought coz of the large pH change associated with s/s titration, methyl orange, phenolphthalein could also b used...

I don't think so, cos with a s/s titration, the equivalence pt is at pH7, but the indicators will still change colour at their respective end points, so the end point will not correspond with the equivalence point.