[JM93]

I've been trying to answer this question and haven't been able to get the correct answer at all:
Determine the pH of the solution after the addition of 1.01 mL of 1.50 M magnesium hydroxide (Mg(OH)2) to 74.2 mL of 0.294 M acetic acid (CH3COOH).

Assume that the volumes are additive and that the 5% approximation is valid.

I've done other examples of these kinds of questions but I keep getting this one wrong. No idea what I'm doing wrong. I did:

1. Finding total volume, so: .00101L + .0742 L = .07521
2.(0.00101L X 1.50M)(2)/.07521L = .0403
3.(.0742L X .294M)/.0201L = .29
4.Log(.0403/.29) = -.857
5. Pka of acetic acid = 4.75. So 4.75 + -.875 = 3.89.

However, it isn't correct. Can someone help me through this?
Thank you.

[Borek]

2.(0.00101L X 1.50M)(2)/.07521L = .0403
3.(.0742L X .294M)/.0201L = .29

You are making us guessing what you did. That often means questions get ignored.

4.Log(.0403/.29) = -.857

You don't have 0.0403 nor 0.29. You ignored the reaction.

[JM93]

I guess to be honest, I really have no idea how to solve this. I was attempting to solve it using the method described in my course but I really don't understand how this whole finding pH thing works and so obviously I'm going about it wrong. I was just wondering if anyone knew how to work the problem out and if they could walk me through it so I could understand it.

[Borek]

You are preparing acetate buffer. Buffer contains an acid and a conjugate base. What is the acid in this problem, and what is the conjugate base?

[JM93]

Nevermind, I actually figured it out. I wasn't setting it up correctly, and I wasn't taking into account that it was Mg(OH)2, and not Mg(OH). (If that makes any sense, chemistry never was my strong suit). Anyway I got it right.