neutralization of HCl with Na OH??

Question

when doing neutralisation reaction(with HCL as acid,NaOH as base and phenolpethlein as indicator)..and adding base from burette dropwise,its color changes to pink.but it is temporary!
how do we know that end point has reached(i-e. acid has been neutralised by base)??
sincere and to the point answers will be appreciated.
please help as i have a chemistry practical of board tomorrow :(

Answer 1

Once the endpoint is reached the pink color will be stable and very faint. You need to stir the solution well and wait a couple of seconds to be sure that the color has stabilized. If you are attempting to quantify the acid concentration, you keep in mind a couple of things. The smaller the drop size and calibration of your pipette, the more accurate your endpoint. Also, when using sodium hydroxide to neutralize HCl, you should use fresh solutions, and the weakest concentration that is practical. Sodium hydroxide absorbs CO2 which will reduce the strength of the base, and can give you an inacurate measurement. And if the strenght of the sodium hydroxide is very strong, you can overshoot the endpoint and the solution will turn dark pink, rather than the pale colour you are looking for.

Answer 2

http://en.wikipedia.org/wiki/Phenolphthalein

I don't have practical experience with Phenolphthalein. This wikipedia article tells a story -- that Phenolphthalein is a poor indicator, and perhaps you should use a good pH meter instead.

Anyway, as you add the droplets of base to your acid&indicator solution, you'll see that the area around where the droplet falls becomes pink momentarily. If you're stirring the acid&indicator constantly, and you continue adding base dropwise, you'll see that the momentary pink lasts longer and covers a bigger area. Keep adding until the whole solution is just barely pink. if you over-add base, it'll apparently turn clear again!

But, according to that wikipedia article, by the time you get to the whole solution to just-barely-pink, you've already more than neutralized the acid, and you're somewhere between pH 8.2 and pH 10. Oh well!

Answer 3

While doing titration experiments this a very common problem. However you need to be patient in these experiments, mixing a drop a time from the time you see the pink color for the first time.

Make sure that you continuosly stir the beaker. Placing a white paper sheet below the beaker always helps. A temporary color is not the right indication of the neutral point. If the color disappears on stirring the solution, it is not the neutral point.

Answer 4

Use phenopthalein as the indicator and place NaOH in the beaker and the acid in the burette.
This is because phenopthalein is pink in NaOH because its natural colour is pink and it is a very weak base itself. When the end point is reached because sufficient acid has been added, the weak base phenophtalein reacts with any additional acid and the solution turns colourless.
So, in end point, the solution in the beaker would be colourless.

Answer 5

when we see the pink color it mean that each molecule of acid has been neutralized by one molecule from the base.hence we reached the end point.
But this color is temporally because the phenolphthalein is combined with CO2 from air and the medium returns to acidic hence, color disappears.

Answer 6

when the pink is temporarily visible, then it means you are approaching end point, and you should continue until a PALE pink stays permanently, (swirl constantly).
if pink is bright, you went over.
you can also calculate it theoretically M1V1 =M2V2

Answer 7

shake the test tube or other container gently as you add the phenolpethlein and continue to until the pink does not go away

Answer 8

Just make sure the examiner's there when colour turns to pink and everything'll be fine