Chemistry Practice Problems Weak Bases Practice Problems Solution: What is the pH of 0.10M diethylamine, (CH3CH2)2NH,...

Solution: What is the pH of 0.10M diethylamine, (CH3CH2)2NH, (Kb=8.6x10-4)?

Problem

What is the pH of 0.10M diethylamine, (CH3CH2)2NH, (Kb=8.6x10-4)?

Solution

Equilibrium reaction:        (CH3CH2)2NH(aq) + H2O(l)  (CH3CH2)2NH2+(aq) + OH-(aq)


Step 1: Construct an ICE chart for the reaction.


Step 2: Write the Kb expression and calculate for Kb.

Kb=productsreactantsKb=[(CH3CH2)2NH2+][OH-][CH3CH22NH]

Solids and liquids are not included in the expression


Step 3: Calculate the equilibrium concentrations.

Kb=xx0.10-xKb=x20.10-x

null

We cannot remove (–x) from the equation

8.6×10-4 (0.10-x)=x20.10-x(0.10-x)8.6×10-5-(8.6×10-4)x=x20=x2+(8.6×10-4)x-8.6×10-5


x=-b±b2-4ac2a

Solution BlurView Complete Written Solution