Solutions Containing Ions Which Do Not Hydrolyse Appreciably
Cl-, NO3-, Br-, I-, ClO4- and SO42- are all the salts of the very strong acids. They are therefore extremely weak bases.(ie. Kb=0) They do not appreciably affect the acidity or alkalinity of an aqueous solution. Na+, K+ and Rb+ and any other alkali metal ion also do not affect the water's pH either. The same is true for the charged ions in Group IIA. Using these generalizations we can predict that solutions of NaCl, KI, BaCl2 and RbNO3 which are made from the above cations and anions are essentially neutral.
 
All other ions tend to cause pH shifts. Cations tend to make solutions more basic whereas anions tend to bring a solution closer to acidity. If both weakly dissociated anions and cations are present then the pH will have to be determined mathematically.
 
Follow-Up Problem
1. Without making any calculations, predict the relative acidity (ie, pH is >, < or =7) of these aqueous solutions.

a) 0.1 mol/L KCl

b) 1.0 mol/L K2CO3

c) 0.1 M NH4NO3

d) 0.1 M NaF

e) 1.1 mol/L Na2SO3
 

2. For question (e) above do the calculations and prove that the pH is what you predicted.
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