Question

1)How does the buffer capacity of the 0.1 M buffer compare when it is titrated with HCl vs NAOH? Is this also true for the 0.2 M Buffer?

2)How does the buffer capacity change with the concentration of the buffer?

3)What would you predict is the buffer capacity of a 0.4 M acetate buffer? Explain why.

Answer 1

Q1

HCl + NaOH = the pH is either very acidic, due to H+ present from HCl or very basic, due to OH- ions in solution

then, buffer capacity

A buffer is any type of substance that will resist pH change when H+ or OH- is added.

This is typically achieved with equilibrium equations. Both type of buffer will resist both type of additions.

When a weak acid and its conjugate base are added, they will form a buffer

The equations:

The Weak acid equilibrium:

HA(aq) <-> H+(aq) + A-(aq)

Weak acid = HA(aq)

Conjugate base = A-(aq)

Neutralization of H+ ions:

A-(aq) + H+(aq) <-> HA(aq); in this case, HA is formed, H+ is neutralized as well as A-, the conjugate

Neutralization of OH- ions:

HA(aq) + OH-(aq) <-> H2O(l) + A-(aq) ; in this case; A- is formed, OH- is neutralized as well as HA.

now...

the same is true for the 0.2 M buffer, it will Last twice of acid/base than the 0.1 M solution buffer

Q2

buffer capacity decreases as we add more acid; since conjguate base is reacted

it also decreases when base is added, since the weak acid is reacting as well

Q3

pH = pKa+ loG(A-/HA)

assume pH = pKa was the goal, aso A- = HA approx

that is, 0.2 M for A- and 0.2 M of HA

the buffer capcity will be 0.2 M of acid /base