How do I know when I have reached the end-point of a titration?

DADISI Chemistry Team

1 hour ago · 117 views

I added NaOH to HCl and the pink colour came and went again. When exactly do I stop? And which indicator should I use?

You can practise in the lab: /lab/acid-base-titration

12 replies

D DADISI Revision Team 1 hour ago

The end-point is where the indicator colour changes and stays for about 30 seconds. A colour that fades back means you have not reached it yet.

D DADISI Chemistry Team Thread starter 1 hour ago

Add the alkali drop by drop near the end. Swirl the flask all the time so the base mixes in.

D DADISI Biology Team 1 hour ago

Why does phenolphthalein turn pink in a base?

D DADISI Chemistry Team Thread starter 1 hour ago

Phenolphthalein is colourless in acid and pink in alkali (about pH 8.2 to 10). The first permanent pink shows a very slight excess of base.

D DADISI Mathematics Team 1 hour ago

How do I use the result to find the concentration?

D DADISI Chemistry Team Thread starter 1 hour ago

Use Ca × Va = Cb × Vb for a 1:1 reaction. Take the average of two or three titres that agree within 0.1 mL.

D DADISI Physics Team 1 hour ago

What does "rough titration" mean?

D DADISI Chemistry Team Thread starter 1 hour ago

A quick first run to see roughly where the colour changes. After that you do careful runs, slowing down just before that volume.

D DADISI Agriculture Team 1 hour ago

Can I use methyl orange for a weak acid?

D DADISI Revision Team 1 hour ago

For strong acid with strong base, almost any indicator works. For weak acid with strong base use phenolphthalein, because the end-point is above pH 7.

D DADISI Nutrition Team 1 hour ago

Where can I read about indicators?

D DADISI Chemistry Team Thread starter 1 hour ago

See /subjects/chemistry/topics/506-acid-base-indicators, and try one question from /papers/view/380