Buffer or not a buffer?

Question

For each of the 4 substances below, suggest a second substance that, when added to a solution of the first, will make a buffer. If a buffer is not possible explain why. If a buffer is possible then write chemical reactions that show how the buffer wil resist changes in pH upon addition of a strong acid or base.

a.sodium hypochlorite
b. perchloric acid
c. sodium carbonate
d.ammonia

Its not a multiple choice, I need to know which can be buffers and which cannot, if they are strong acid or base then they cannot be a buffer, if they are weak then I can and i need to tell what I can add to it to make it a buffer

Answer 1

a. Add HClO, so that the solution contains both a weak acid (HClO) and its conjugated base ClO- (from the dissociation of NaClO -> Na+ + ClO-)

b. You can convert it in a buffer solution because HClO4 is a strong acid.

c. Add NaHCO3. Now the solution contains the conjugate pair of HCO3- (acid) and base (CO3(2-)). Both these anions are produced from the dissociation of the two salts.

d. Add NH4Cl, which dissociates: NH4Cl --> NH4(+) + Cl- and so you have the NH3/NH4(+) pair of conjugated pair of weak base/weak acid.

In any case if in the solution exists the weak acid HA and its conjugate base A-, when you add small quantities of a strong acid the H3O+ are neutralized by A-:

H3O+ + A- --> HA + H2O

When you add small quantities of a strong base the extra OH- are neutralized by HA:

HA + OH- --> A- + H2O

So the pH of the solution doesn't change a lot.

Answer 2

I haven't heard of these being buffers because a buffers takes an acid or base an attempt to help it reach a pH of 7( which is neutral) and the only thing that is neutral is water. The buffers act to keep the pH within normal limits. So if I would choose from the answers above I would choose ammonia.

Answer 3

a. hypochloric acid
HClO <=> (H)+ + (ClO)-

c. sodium bicarbonate
(HCO3)- <=> (H)+ + (CO3)2-

d. ammonium chloride
(NH4)+ <=> (H)+ + NH3

in each case, addition of H+ shifts the equilibrium to the left
and addition of OH-, which means removal of H+, shifts the equilibrium to the right

b. perchloric acid cannot be used to form buffer solution as it is a strong acid. A buffer must consists of a weak acid and its conjugate base, or a weak base and its conjugate acid, hence forming a dissociation equilibrium. Perchloric acid dissociates completely in water. It doesn't form an equilibrium.