Indicators? Please Explain?

[luken93]

So I wouldn't say that the textbook really explains it well, but from what I can gather (using the picture attached as reference)

When determining a suitable indicator, you need look at where there is a steep gradient. Once you have determined this range, you need to find an indicator whose values lie between the corresponding start and end pH points of the steep gradient.

So for a), you would need an indicator whose values lie between 3~10.5, and for b), you'd need an indicator that lies between 3~7?

Hopefully this is right?

[azn_dj]

OK here is a simple way of putting it:

Strong acid with strong base - one that will change colour around pH of 7
Weak acid with strong base - one that will change colour quite a bit above a pH of 7 (hence 8 or 9)
Strong acid with weak base - one that will change colour quite a bit below a pH of 7 (hence 6, 5, or 4)
Weak acid with weak base - test fails. Use back titration.

[dptjandra]

You've both got a pretty clear picture of what you need to do.  Basically you want the indicator to change colour (the end point) to be as close to the equivalence point as possible (which is marked on the graph by a steep curve).

The exact explanation for the shape of the curve and the pH at which equivalence occurs requires a slightly more lengthy explanation (and some consideration of equilibria) which will probably confuse you more than help you

[luken93]

Ok, so what I've said should enable me to do pretty much all questions in Unit 3 Chem?
That's all I need to know haha

[luken93]

Oh I just realised we can upload stuff again, so I've attached the original question I was talking about

[dptjandra]

I think for the sake of the titration part of the course, yes.