General Chemistry/Reactions of Acids and Bases

Overview
To summarize the properties and behaviors of acids and bases, this chapter lists and explains the various chemical reactions that they undergo. You may wish to review chemical equations and types of reactions before attempting this chapter.

The following reactions are net ionic equations. In other words, spectator ions are not written. If an ion does not partake in the reaction, it is simply excluded. The spectator ions can be found because they occur on both the reactant and the product side of the equation. Cross them out and rewrite the equation without them. Of course, the coefficients must be equal.

Canceling out the spectator ions explains the net of net ionic equations. The ionic part means that dissolved compounds are written as ions instead of compounds. Acids, bases, and salts are all ionic, so they are written as separate ions if they have dissociated.

As an example, sodium bicarbonate (NaHCO3) would be written as Na+ and HCO3- because the salt will dissociate, but the bicarbonate will not dissociate (it's a weak acid).

Neutralization
When an acid and a base react, they form a neutral substance, often water and a salt.

First, let's examine the neutralization of a strong acid with a strong base.

Now, let's see some examples involving weak acids and weak bases.

Many reactions result in the formation of gas bubbles or a solid precipitate that will make the solution cloudy. The last equation brings up an interesting application. Many rocks and minerals contain calcium carbonate or calcium bicarbonate. To identify these rocks, geologists can perform the "acid test". A drop of acid is applied, and the presence of gas bubbles indicates carbonate.

Here are more examples of neutralization reactions.

Anhydrides
An anhydride is a substance that does not contain water. More specifically, it is a substance that reacts with water to form an acid or base. Anhydrides are usually in the form of a gas that dissolves into water and reacts to form an acid or base. They can also be solids that will react with water.

The main difference between those two equations is the fact that nitrous acid is weak and thus does not dissociate, whereas nitric acid is strong and dissociates into ions.

Here are a few more examples of anhydride reactions.

It is important to remember which acids are strong and which are weak. Review this if necessary.

For example, sulfur dioxide gas (acidic anhydride) is bubbled through a solution of calcium hydroxide (basic).

Here are more examples.

Remember that water is involved in these reactions, but it is not written if it occurs on both sides of the equation.

Hydrolysis
A salt of a weak acid and strong base dissociates and reacts in water to form OH-. A salt of a strong acid and weak base dissociates and reacts in water to form H+. This process is called hydrolysis.

In this first example, aluminum nitrate is dissolved in water.

The solution is acidic not because nitric acid is strong, but because aluminum is a weak base.

Here is an easier example.

Lewis Acids/Bases
Lewis acids accept an electron pair. Lewis bases donate an electron pair. Together they react and bond to form an adduct.

Lewis acids/bases do not require the presence of water. However, H+ can be thought of as a Lewis acid because it accepts electron pairs. OH- can donate an electron pair, making it a Lewis base.

Practice Problems
Write the net ionic equations for the following. Make note of any solid precipitates or gas bubbles that would form.

Answers to Practice Problems
 * 1) Equimolar solutions of sodium biphosphate and potassium hydroxide are mixed.
 * 2) Equimolar solutions of sodium biphosphate and hydrochloric acid are mixed.
 * 3) Excess sulfur dioxide gas is bubbled into a dilute solution of sodium hydroxide.  Acid is then added.
 * 4) Aluminum chloride is dissolved into water.
 * 5) Sodium fluoride is dissolved into water.  Strong acid is then added.
 * 6) Solid calcium oxide is exposed to a stream of sulfur trioxide gas.  If the resulting compound is dissolved, will the solution be acidic, basic, or neutral?
 * 7) Gaseous hydrogen chloride is bubbled into a solution of silver nitrate.
 * 8) Ammonium chloride crystals are dissolved in water.  Sodium hydroxide is then added.
 * 9) Calcium hydroxide crystals are dissolved into a solution of sodium bicarbonate.
 * 10) Phosphine gas is sprayed onto pebbles of aluminum trichloride. (Hint: these are Lewis acids/bases.)