Question

Titration Lab

Why are air bubbles in buret tip a possible source of error in a titration experiment?

When you reached the endpoint, the color of the solution went from colorless to a light pink. What does the endpoint tell you?

Answer 1

In a titration experiment ( which is a estimation technique to determine unknown concentration of a substance by reacting with a substance of known concentration ), one of the component is taken in burette and other is taken in a conical flask ( as shown in fig I).

Figure 1

Now, air bubbles in burette tip a possible source of error in titration experiment because during titration when the liquid is dropped inside the conical, a part of the measurement will be air, so actual volume of liquid added will be less than the burette reading means there will a small positive error (burrette reading will be higher than actual).

So before titration, remove air bubbles from burette tip by filling burette with titrant and then open the tap with full speed so that all air is flushed out.

Phenolphthalein is colourless in acidic solution and pink in basic solution. So, during acid base titration if phenolphthalein is used as indicator (few drops of phenolpthalein is added to the acidic solution taken in conical) , at the end point of the titration, when one drop excess of base is added through burette, the colourless ( acidic) solution turned to light pink (basic).