1. An aqueous solution of 0.055 M KCN is made. At equilibrium this solution will

ID: 960483 • Letter: 1

Question

1. An aqueous solution of 0.055 M KCN is made. At equilibrium this solution will be

A) Acidic

B) Basic

C) Neutral

2. Suppose you need to calculate the pH of an aqueous KCN solution. How many of these statements should you be thinking about in advance?

pH should be < 7

-log[x] = pOH not pH

don't forget pH = 14 - pOH

pH should be > 7

The mass action equation will be set equal to Ka

pH = -log[x]

I need an ICE table and a Kb or Kw/Ka

3. What reaction would you use in an ICE table to calculate the pH of a KCN solution?

CN- + H2O HCN + OH-

KCN (s) K+ + CN-

H+ + OH- H2O

CN- + H2O HCN + H3O+

4. What is the pH of a 0.055 M KCN solution. The Ka for HCN is 8.0×10-10

1) KCN is salt of weak acid and strong base so its aqueous solution is basic in nature.

2) pH should be > 7 , I need an ICE table and a Kb or Kw/Ka

3) CN- + H2O HCN + OH-

4) pH = 1/2 (pKw + pKa + log C)

pH = 1/2 (14 + (-log 8.0 x 10-10) + log 0.055)

pH = 10.9

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