Prelab Exercise 3. Consult an appropriate table of acid dissociation constants.

Question

Prelab Exercise 3. Consult an appropriate table of acid dissociation constants. For each of the following pH's give the 1. (a) Determine the pH of the solution that formula of an appropriate weak acid and its from the results conjugate base that would be suitable for preparing pure addition of 5 mL of 0.1 M HCl to 50 mL of a buffer of the desired pH water. (a) desired buffer pH 3.5 (b) desired buffer pH E 7.3 (b) Compare the change in pH expected when the same amount of acid is instead added to the SO (c) desired buffer pH 10.0 IHSO3 buffer described in the introduction. 2. Determine the moles of NaOH that could be absorbed by the SO32lHSO3 buffer described in the introduction before the base absorbing capacity of this buffer is destroyed

Explanation / Answer

1)

moles of HCl = 0.1 x 5 / 1000 = 5 x 10^-4

moles of water = moles of HCl

M x 50 = 5 x 10^-4

M = concentration of pure water = 1 x 10^-5 M

pH = -log [H+] = -log [1 x 10^-5]

= 5

pH = 5

3)

a)

weak acid = HCOOH

conjugate base = HCOO-

b)

weak acid = H2AsO4-

conjugate base = HAsO42-

c)

weak acid = HCO3-

conjugate base = CO32-

Note : you did not mention any introduction here

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