[Luisa2901]

Hey, guys! I want some help with this problem. I have a text on Monday and I don't know how to answer it.

In the titration of 25 mL of a 0.100 mol/L aqueous solution of Ammonium Hydroxide (pKb = 4.74), 0.100 mol/L hydrochloric acid was utilized in the presence of the cresol red indicator (pH range = 7.0 - 8.8, transitioning from yellow to red). When the first persistent color change occurs, is the environment considered neutral? If the answer is negative, what exact additional volume of one of the solutions below would be required to achieve a neutral medium:

a) Sodium Chloride 0.100 mol/L;
b) Hydrochloric acid 0.100 mol/L;
c) Calcium Hydroxide 0.100 mol/L

I have calculated the initial pH of the solution:
NH4(OH)-->NH4+ + OH-
0.1                0          0
-X                 +X      +X
0,1-X             X          X

Considering Kb=1,8.10^(-5) I found [OH-]=0,0013326 so the pH is 11,12.
I know the solution will start changing color at pH=8.8, but I am not sure what to do with it.

[Borek]

Please read the forum rules, you have to show your efforts at answering the question to receive help.

What is the initial pH of the solution? (approximately, there is not enough information for an exact answer)

At what pH do you expect the solution to start changing color?

[Luisa2901]

Sorry about that, I've corrected my post.

[Borek]

I know the solution will start changing color at pH=8.8, but I am not sure what to do with it.

That's the important part.

You need to get from 8.8 to neutral - does it mean adding acid, or base?

[Luisa2901]

I get it now, thank you