Acid-Base Cheat Sheet
One difficult aspect of acid-base chemistry is recognizing what types of species are
present in solution, i.e., whether a species is a strong acid, strong base, weak acid, weak
base or a neutral species. Below are some ideas and generalizations to keep in mind that
will help in recognizing types of species present.
1. Memorize the following strong acids: HCl, HBr, HI, HNO3, NClO4, and H2SO4
2. Memorize the following strong bases: LiOH, NaOH, KOH, RbOH, Ca(OH)2,
Sr(OH)2 and Ba(OH)2
3. For weak acids Kw < Ka < 1 (Ka can be found Table 14.3)
4. Conjugate bases of weak acids are weak bases - Kw < Kb < 1
5. All conjugate acids of weak bases are weak acids - Kw < Ka < 1
6. Alkali metal ions and heavier alkaline earth metal ions (Ca2+, Sr2+, Ba2+) have no
acidic or basic properties in water.
7. All conjugate bases of strong acids have no basic properties in water (Kb << Kw)
and only HSO4- has any acidic properties in water.
Steps for solving acid-base problems
1. List the major species in solution
2. Look for reactions that can be assumed to go to completion (i.e. a strong acid
dissociating or H+ reacting with OH-)
3. For a reaction that can be assumed to go to completion:
a. Determine the concentration of the products
b. Write down the major species in solution after the reaction
4. Look at each major component in the solution and decide if it is an acid or a base.
5. Pick the equilibrium that will control the pH. Use known values of K for the
various species to help decide the dominant equilibrium
a. Write the equation for the reaction and the equilibrium expression (Law of
mass action)
b. Calculate the initial concentrations (assume the dominant equilibrium has
not yet taken place)
c. Define x
d. Compute the equilibrium in terms of x
e. Substitute into the equilibrium expression and solve for x
f. Check validity of any approximations made
g. Calculate the pH or any other concentrations as required.