[Borek]

4.78 is not a correct answer to 2. - it would mean pH goes up after adding acid. I have not checked numbers, but your result (4.71) looks more reasonable. Perhaps they switched the answers.

[ghostanime2001]

When I use HH equation the answers come out right even with adding acid the answer comes out to 4.780. I don't understand why the HH equation gives the wrong answer and using the Ka method gives the right answers. I don't even know which is right anymore

[Borek]

I don't understand why the HH equation gives the wrong answer

Then you are doing something wrong. HH equation gives the correct answer.

Besides, answers as listed do look dubious. Think about it. After you add an acid, pH goes... up? After you add a base pH goes... down? It should be the other way around.

Correct answers are 4.74, 4.71. 4.78 (in this order - problems 1., 2., 3.)

[ghostanime2001]

Yeah I just noticed that I derived the HH equation wrong. By mistake I had [HA] in the numerator and [A^-] in denominator. When I substituted my values into the right HH equation I got a pH of 4.71 for 2. and 4.78 for 3. The same answers for when I did it with only ICE tables.

please take a thorough look at the image shack uploads. I get the same answers as that when using the HH equation. You can verify my answers with the HH equation.

[Borek]

Your answers are identical with mine, no need for a detailed check. What I have seen skimming looks OK.