Question

In this lab, we will observe how weak acid solutions can work as a buffer. In this context, "buffer" refers to a solution that maintains a nearly constant pH, which is essential for biological systems to function properly. For example, the pH of human blood varies only slightly between the values of 7.35-7.45. Which of the following statements is true regarding the "buffer" in this context? "Buffer" refers to any solution that contains acid and base. All buffers can maintain a nearly constant pH at pH.6-8. Weak acids, such as phosphoric acid, can be used as buffers. Amino acid solutions cannot work as buffers because they have more than one pKa values.

Answer 1

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,

For the weak base equilibrium:

B(aq) + H2O(l) <-> BH+(aq) + OH-(aq)

Weak base = B;

Conjugate acid = BH+

Neutralization of OH- ions:

BH+(aq) + OH-(aq) <-> B(aq) + H2O(l); in this case, OH- is neutralized by BH+, as well as B is created

Neutralization of H+ ions:

B(aq) + H+(aq) <-> BH+(aq)

then

option i) can't be since, it must be their respecti acid/conjugate

option ii) false, buffer ragne depend on pKa

option iii) TRUE, weak acids couild be used if we add base or conjugates

option iv) False, we can, acutally it is a specie used in pKa buffering