Question

What indicator is better in the following titrations :

1) strong acid/strong base
a) methyl red (4.4 - 6.2 )
b) bromophenol blue (6.2 - 7.6 )

2) strong acid/weak base
a) methyl orange (3.1 - 4.4 )
b) bromophenol blue (3.0 - 4.6 )

3) weak acid/strong
a) phenolphthalein (8.0 - 10.0 )
b) phenol red ( 6.4 - 8.0 )

and why ?
Please explain
thank a lot

Answer 1

The equivalence point for
#1 is 7; therefore, you want an indicator that turns at about 7 which is b rather than a.
#2 I think has a typo. You have bromophenol blue changing differently than for 1. The eq pt for #2 is acidic and methyl orange should do.

#3 has a typo too. I think yo means weak acid/strong base. The eq pt is basic (about 8.5 or so) and a will do nicely and should do better than phenol red.