Aqueous Salt Solutions - Acid and Base Properties
Salts contains ions that may affect the pH in aqueous solutions in both acidic and basic directions.
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It is possible to predict whether an aqueous solution of a salt with both basic and acidic properties will be basic, acidic or neutral by comparing the Ka value for the acidic ion with the Kb value for the basic ion.
See also Strong and weak acids and bases and Buffer solutions, as well as pKa of inorganic acids and bases, pKa of phenols, alcohols and carboxylic acids and pKa of amines, diamines and cyclic organic nitrogen compounds.
| Ka vs Kb | pH | Basic or acidic |
| Ka > Kb | < 7 | Acidic |
| Ka < Kb | > 7 | Basic |
| Ka = Kb | 7 | Neutral |
This table summarizes the acid-base properties of aqueous solutions of various salts:
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| Type of salt | Examples | pH of solution | Comment | |
| Cation from | Anion from | |||
| Strong base | Strong acid | BaCl2, KCl, CaNO3, Na2SO4 | Neutral | Neither acts as an acid or a base |
| Strong base | Weak acid | NaF, KCHOO, NaHCO3 | Basic | Anion acts as a base Cation has no effect on pH |
| Conjugate acid of weak base | Strong acid | NH4Br, NH4NO3, |
Acidic | Cation acts as an acid Anion has no effect on pH |
| Conjugate acid of weak base | Conjugate base of weak acid | NH4CN, NH4CH3COO | Acidic if Ka > Kb Basic if Kb > Ka Neutral if Ka = Kb | Cation acts as an acid Anion acts as a base |
| Highly charged metal ion | Strong acid | Al(NO3)3, CrCl3 | Acidic | Hydrated cations acts as an acid Anions has no effect on pH |
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