# PH with 2 acids

1. Feb 19, 2006

### firyace

Hi, I got a problem with something regarding to chemistry. How can you determine the pH of a solution with two Acids?

The question says that A 50.00 mL aqueous solution is made by mixing the following two solutions:

10.00mL 1x10^-9M HCl

50.00mL 1*10^-4 M CH3COOH (Ka= 1.8*10^-5)

a) What is the Cl^- in the 50.00mL solution?
b)What is the pH in the 50mL solution?
c) What is the [CH3COOH] in the 50mL solution?

thanks!

2. Feb 20, 2006

### Staff: Mentor

In general it is difficult to calculate pH of such solution, but here... Look at the concentration of hydrochloric acid. What pH does it have without acetic acid?

3. Feb 20, 2006

### ksinclair13

This is my guess (please take this lightly):

The contribution of H+ from the HCl will be negligible compared to the contribution from water, which would make the pH of the first solution 7.00. To figure out the pH of the other solution, just do a regular equilibrium problem using the acetic acid. The initial H+ concentration will be 1.0 x 10^-9, but I don't think it will matter because it's negligible.

Note: I'm confused as to why the question says that a 50 mL solution is formed instead of a 60 mL solution...

4. Feb 20, 2006

### Staff: Mentor

You are correct on both accounts - pH and volume ;)

5. Feb 21, 2006

### firyace

So now I am confused, do I just neglect the HCl totally because that the concentration is neglegible?

that is what it said for the question.

6. Feb 21, 2006

Yes.