Question

Calculate the concentration of acetic acid and acetate ion in a 0.2 M acetate buffer at pH 5. The p K a of acetic acid is 4.76

Answer 1

The concentration of acetic acid in the 0.2 M acetate buffer at pH 5 is 0.075 M, and the concentration of acetate ion is 0.130 M. This was calculated using the Henderson-Hasselbalch equation with the given pH and pKa.

Step-by-step explanation:

We can calculate the concentration of acetic acid and acetate ion in a 0.2 M acetate buffer at pH 5 using the Henderson-Hasselbalch equation. The equation is pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the acetate ion and [HA] is the concentration of acetic acid. Given that pKa of acetic acid is 4.76 and the pH of the buffer is 5, we can rearrange the equation to solve for the ratio of [A-] to [HA].

pH = pKa + log([A-]/[HA])

5 = 4.76 + log([A-]/[HA])

log([A-]/[HA]) = 5 - 4.76

log([A-]/[HA]) = 0.24

When we take the antilog of both sides, we get:

[A-]/[HA] = 10^0.24

[A-]/[HA] = 1.737

Since we know the total concentration of the acetate buffer is 0.2 M, we can set up the following expressions:

[A-] + [HA] = 0.2 M

[A-] = 1.737 x [HA]

By combining and simplifying these equations, we can solve for [A-] and [HA]:

[HA] = 0.2 M / (1 + 1.737)

[HA] = 0.075 M

And, therefore, the acetate ion concentration [A-]:

[A-] = 1.737 x 0.075 M

[A-] = 0.130 M

Thus, the concentration of acetic acid is 0.075 M and the concentration of acetate ion is 0.130 M in a 0.2 M acetate buffer at pH 5.

Answer 2

[Acetic acid] = 0.07 M

[Acetate] = 0.13 M

Step-by-step explanation:

pH of buffer = 5

pKa of acetic acid = 4.76

`pH=p_(Ka) + log([Salt])/([Acid])`

Now using Henderson-Hasselbalch equation

`5=4.76 + log([Acetate])/([Acetic\;acid])`

`log([Acetate])/([Acetic\;acid]) = 0.24`

`([Acetate])/([Acetic\;acid]) = 1.74` ....... (1)

It is given that,

[Acetate] + [Acetic acid] = 0.2 M ....... (2)

Now solving both the above equations

[Acetate] = 1.74[Acetic acid]

Substitute the concentration of acetate ion in equation (2)

1.74[Acetic acid] + [Acetic acid] = 0.2 M

[Acetic acid] = 0.2/2.74 = 0.07 M

[Acetate] = 0.2 - 0.07 = 0.13 M