Finding the pH of this acid and its sodium salt solution

[Kaushik]

Homework Statement

The Ionization constant of chloroacetic acid is $1.35 * 10^{-3}$. What will be the pH of 0.1M acid and its 0.1M sodium salt solution?

Relevant Equations

$K_w = K_a * K_b$, $K_b = \frac{[OH^-][CH2ClOOH]}{[CH2ClOO^-]}$

For finding the pH of the acid, I made use of the equilibrium law (or the law of mass action) to arrive at the degree of dissociation which I later used to get the [H+] concentration.

I am stuck in finding the pH of the salt solution.

$CH2ClOO^- + H2O <---> CHClOOH + OH^-$

Could you please help me out?

 

[epenguin]

The template asks you to write down the relevant equations. You have not done so, not even the ones you used to get your result so far. It is however however an essential step for this kind of problem.

 

[Borek]

Finding pH of a weak acid is not different from finding pOH of a weak base. If you know how to do the former, just follow the same approach to do the latter.

 

[Kaushik]

Finding pH of a weak acid is not different from finding pOH of a weak base. If you know how to do the former, just follow the same approach to do the latter.

So is it an acidic buffer?

 

[epenguin]

So is it an acidic buffer?

Your problem is about a salt.

 

[Borek]

No buffer here.

When you have solution of an acid, you can calculate concentration of H⁺ from the known initial concentration of the acid and its dissociation constant.

When you have solution of a base, you can do exactly the same, just instead of H⁺ you will be calculating concentration of OH^-.

 

[epenguin]

The template asks you to write down the relevant equations. You have not done so, not even the ones you used to get your result so far. It is however however an essential step for this kind of problem.

Oh well, this is not the first or second time that for a problem in this area I asked for the relevant equations and that ended the thread. So I suppose as soon as you write them down you know what to do. (Ready to help but I do wonder sometimes when I see a question about some extremely standard calculation which is in all the books with worked examples!)

Anyway, for all these pH problems it is always the same, there are three equations (or for rare more complicated problems three types of equation) plus some simplifying assumptions or approximations which are essential to learn about, and also have a grasp of how good they are and their limits.

I got pH = 7.94

 

[chemisttree]

Oh well, this is not the first or second time that for a problem in this area I asked for the relevant equations and that ended the thread. So I suppose as soon as you write them down you know what to do. (Ready to help but I do wonder sometimes when I see a question about some extremely standard calculation which is in all the books with worked examples!)

Anyway, for all these pH problems it is always the same, there are three equations (or for rare more complicated problems three types of equation) plus some simplifying assumptions or approximations which are essential to learn about, and also have a grasp of how good they are and their limits.

I got pH = 7.94

-10 pts for using the wrong # of significant figures!