Question

The indicator phenolphthalein is colorless in an acidic solution and is red when the solution becomes basic. The transition range is @ pH 8.0 - 9.6. Which direction of titration, HCl by NaOH or NaOH by HCl, would give better precision and accuracy? Or does it matter?

Answer 1

Titration of HCl by NaOH gives the better precision and accuracy.

Because addition of phenolphthalein to acid (HCl) gives colourless solution, which is being titrated changes its colour its colur to red which can be easily be detected.

That means, colour change at equivalence point can be easily detected because of change is from colourless to red. (coloured)

But reverse is not that much easy to detect the correct end point where colour changes from red to clourless which is not sharp.