2. Label each of the following compounds as either strong acid (sa), weak acid (

Question

2. Label each of the following compounds as either strong acid (sa), weak acid (wa), strong base (sb), weak base (wb),amphoteric (pp) or neutral salt (n) (a) 0.05 M NaCl (b) 0.05 M Acetic Acid (c) 0.05 M Sodium Acetate (d) 0.05 M KH2PO4 (e) 0.05 M Tris [(CH2OH)CNH2l (f) 0.05 M Na CO (g) 0.05 M HCl 3. Calculate the original pH of 25 mL of each solution 4. Calculate the pH following the addition of 1 mL of 0.10 M HCl to 25 mL of each solution 5. Calculate the pH following the addition of 1 mL of 0.10 M NaOH to 25 mL of each solution.

Explanation / Answer

Q2.

a) neutral salt

b)weak acid

c) basic salt, from weak acid/base

d)amphoteric

e) amphoteric

f) weak base

g) strong acid

Q3.

a)

pH of NaCl, a neutral salt, Na+ and Cl- should be pH = 7, since it is neutral by definition

b)

Acetic acid is a weak acid, so

HA <> H+ + A-

Ka = [H+][A-]/[HA]

1.8*10^-5 = x*x/(0.05-x)

x = H = 9.39*10^-4

pH = -log(H) -log(9.39*10^-4) = 3.027

c)

For sodium acetate, this is a basic salt, since

NaAc = Na+ + Ac-

Bu Acetate is a conjguate so:

Ac- + H2O = HAc + OH-

Kb = [HA][OH-]/[A-]

Kb = Kw/Ka) = (10^-14)/(1.8*!0^-5) = 5.55*10^-10

solve

5.55*10^-10 = x*x/(0.05-x)

x = OH = 5.267*10^-6

pOH = -log(5.267*10^-6) = 5.278436

pH = 14-pOH = 14-5.278436 = 8.721564

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