Titration Of Naoh And Hcl

KarenLo · Jan 31, 2005

How to answer the question: why the pink colour (from 2-3 phenolphthalein indicator) obtained at the end point of the titration in this experiment gradually disappears over time?

Is it because of that the water will contrary back to the form of H+ and OH-?

cronxeh

Equilibrium shifts towards the side where pH is acidic.

KarenLo · January 31, 2005

can you tell me in more item?
you mean HCl + NaOH --> NaCl + H2o? or BaCO3 + HCl --> BaCl2 + H2o + CO2??

chem_tr

Hi, I remember phenolphthalein begins to decompose with increasing hydrolysis over time. The quinoid class is pinky-majestic, but with increasing hydrolysis, acidic products develop and every bit cronxeh said, the pH is lowered. It is very likely that the carbon dioxide in the medium causes the pH drop, as information technology gives carbonic acid with water.

cronxeh · May 1, 2017

http://www.elmhurst.edu/~chm/vchembook/images2/186phenolph.gif [Broken]

It depends on which way the reaction went - either increasing in pH (from 8.2 to 10 - condign red color) or decreasing in ph (becoming acidic and dropping from viii.2 down - colorless)

So in your case you lot are asked (probably) to add phenolphtalein into HCl, and so gradually make drops of NaOH while stirring it.

What happens is that phenolphtalein is colorless at first (becomes the environs is acidic - HCl), and stirring the mixture while neutralizing it (adding NaOH) insures that you dont get fooled by forming pink bubbles at individual spots

What happens next is out of my realm but I'chiliad going to imagine hither, so carry with me:
phenolphtalein + HCl --> HC2H3O2 (phenolphtalein added to HCl, the pH is less than eight.ii - its colorless)

You titrating (neutralizing):
HC2H3O2 + NaOH --> Na(C2H3O2) + H2O (the pH raises around 8.ii to ten depending on how vigorously you titrate)

Now during this titration reaction the electrons are costless to move between phenolphtalein-HCl juncture and if y'all terminate titrating the color will disappear and pH would drop into acidic range

AFAIK if you titrate fully and reaction is complete the color will stay pinkish/red depending how much NaOH u added

chemisttree

Phenolthalein does Non decompose at its endpoint pH.
Phenolthalein does NOT re-equilibrate to produce an acidic product at its endpoint pH.

Slightly basic solutions Exercise absorb CO2 from the air and produce the weak acid HCOOOH. The absorption happens fairly slowly and a faint pinkish endpoint will gradually fade. Adding more NaOH after the faint endpoint is reached (producing a darker endpoint) will crusade the pink solution to persist much longer but also results in an inaccurate titration and should be avoided. When I'm grading a student's lab technique score, these dark endpoints are a guaranteed low score!