H2S+H2O<-> H3O +HS
why THIS BUFFER SOLUTION IS ABLE TO RESIST CHANGE IN PH WHEN SMALL AMOUNTS OF OH ARE ADDED TO IT.
Frankly, I don't think it is a very good buffer; however, small amounts of OH will be neutralized by the H3O^+ but I wouldn't bank on it.
To understand why this buffer solution is able to resist changes in pH when small amounts of OH- are added to it, we need to examine its components and their behavior.
A buffer solution is a solution that can resist changes in pH when an acid or a base is added to it. It consists of a weak acid and its conjugate base (or a weak base and its conjugate acid). In this case, the components of the buffer solution are H2S (weak acid) and HS- (conjugate base).
When H2S is dissolved in water, it partially dissociates into H3O+ (hydronium ion) and HS-. The dissociation can be represented as follows:
H2S + H2O <-> H3O+ + HS-
Now, let's examine what happens when a small amount of OH- (hydroxide ion) is added to the buffer solution.
OH- + H3O+ <-> 2H2O
The added OH- reacts with the H3O+ to form water molecules. This reduces the concentration of H3O+ in the solution.
However, in the reaction between H2S and water, some of the H2S will react with the OH- to form HS-. This helps to replenish the concentration of the HS- in the solution.
H2S + OH- <-> HS- + H2O
The equilibrium between H2S and HS- shifts to the left, producing more HS-. This maintains the concentration of the conjugate base in the buffer solution.
Overall, the buffer solution resists changes in pH because the OH- ions added to the solution are consumed in reactions that either form more water or react with the weak acid to form its conjugate base. This helps to maintain a relatively constant concentration of H3O+ (or pH) in the solution, even when small amounts of OH- are added.
In summary, the buffer solution made up of H2S and HS- can resist changes in pH when small amounts of OH- are added because the added OH- ions are consumed in reactions that form water or react with the weak acid, helping to maintain a relatively constant concentration of H3O+ (or pH) in the solution.