Explore how acids and bases behave in solution and what happens at the molecular scale when they react — considering the strenghts of the acids and bases, and whether they are neutral compounds or ions.
Section 1
Acids and Bases in Solution
An acid-base reaction is one in which an H+ ion is transferred from the acid to the base. The H+ ion is often described as a proton, so acids are proton donors and bases are proton acceptors. Both acids and bases can be categorized as either strong or weak.
Strong Acids
Dissolve in water and ionize fully to give the H+ ion and its resulting counter ion. The free H+ ion is available to react with a base.
Strong Bases
Are soluble hydroxide salts. When they dissolve in water, they produce OH− ions that can accept an H+ ion from an acid to produce water, H2O.
Weak Acids
Dissolve in water but do not fully ionize. While they remain intact, the acidic H atom can be donated as an H+ ion to a base.
Weak Bases
Are soluble in water and can react to accept an H+ ion from an acid.
Watch the animations below to see how each type of acid or base behaves in aqueous solution.
Strong acid — HNO₃
Think about it: Compare the strong and weak acid animations. What difference do you observe in how the reactions take place?
Section 2
Acid-Base Reactions
An acid-base reaction is one in which an H+ ion is transferred from the acid to the base. These reactions can be categorized based on whether the acids and bases involved are strong or weak — and each combination produces a distinctly different outcome at the molecular scale.
Strong acid – strong base — HCl and NaOH
Notice: In all strong acid–strong base reactions, the base is the OH- ion and the resulting product is water, H2O.
Section 3
Neutral and Ionic Acids and Bases
In an acid-base reaction, all acids donate H+ ions and all bases accept H+ ions. The acid and base reactants need not be neutral compounds — they can be ions. The most common of these situations involve anions that act as weak bases.
Compare the two animations below: one involves a neutral base, the other an anionic base. Notice how the identity of the base — whether it is a molecule or an ion — affects the reaction.
Strong acid – neutral base — HCl and NH₃
Key idea: The weak base NO2− ion is supplied by the soluble salt, NaNO2. After NaNO2 dissolves and dissociates, the NO2− ion is available to accept a proton from the acid.