Buffer #1: 0.15 M HF(aq) and 0.10 M NaF(aq)
Buffer #2: 0.090 M HF(aq) and 0.060 M NaF(aq)
Fill in the following sentence:
The pH values of Buffers #1 and #2 are _______, and the buffering capacity of Buffer #1 is _______ than that of Buffer #2.

a) unequal; higher
b) equal; lower
c) unequal; lower
d) equal; higher

Respuesta :

Buffer #1: 0.15 M HF(aq) and 0.10 M NaF(aq)   Buffer #2: 0.090 M HF(aq) and 0.060 M NaF(aq). The pH values of Buffers #1 and #2 are equal, and the buffering capacity of Buffer #1 is higher than that of Buffer #2.

A buffer is a solution that is capable of withstanding changes in pH caused by the introduction of acid or base substances. It may neutralize tiny quantities of additional acid or base, allowing the pH of the solution to remain reasonably constant.

For buffer 1;

  • [HF] = 0.15 M
  • [NaF] = 0.10 M

Under Standard Conditions, Ka(acid dissociation constant) for HF = 3.5 × 10⁻⁴

pKa = -log Ka

pKa = -log (3.5 × 10⁻⁴)

pKa = 3.454

The formula for calculating the buffer value can be represented by:

[tex]\mathbf{pH = pKa + log \dfrac{([A^+])}{([HA])}}[/tex]

[tex]\mathbf{pH = 3.454 + log \Big(\dfrac{0.10}{0.15}}\Big)[/tex]

pH = 3.2779

For Buffer 2;

  • [HF] = 0.090 M
  • [NaF] = 0.060 M

[tex]\mathbf{pH = 3.454 + log \Big(\dfrac{0.06}{0.09}}\Big)[/tex]

pH = 3.2779

We can see that the pH of buffer 1 is equivalent to the pH of buffer 2.

Buffer capacity measures a solution's capacity to endure pH fluctuations by either accepting or detaching H+ and OH- ions.

For Buffer 1:

The buffer capacity can be expressed by using the formula:

[tex]\mathbf{\beta = \dfrac{2.3 \ Ka [H^+] [C]}{(Ka+ [HA])^2}}[/tex]

where;

  • C = total concentration of buffer components i.e.  [HA] + [A⁻]

[tex]\mathbf{\beta = \dfrac{2.3 \ \times 3.5 \times 10^{-4} \times (0.15) (0.15 \times 2)}{(3.5 \times 10^{-4} + (0.15)^2 }}[/tex]

[tex]\mathbf{\beta = \dfrac{3.6225 \times 10^{-5}}{0.02260}}[/tex]

[tex]\mathbf{\beta = 0.0016}[/tex]

For Buffer 2:

[tex]\mathbf{\beta = \dfrac{2.3 \ \times 3.5 \times 10^{-4} \times (0.09) (0.09 \times 2)}{(3.5 \times 10^{-4} + (0.09)^2 }}[/tex]

[tex]\mathbf{\beta = \dfrac{1.3041 \times 10^{-5}}{0.008163}}[/tex]

[tex]\mathbf{\beta = 0.00159}[/tex]

Therefore, we can conclude that the pH values of Buffers #1 and #2 are equal, and the buffering capacity of Buffer #1 is higher than that of Buffer #2.

Learn more about buffers here:

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