Acids, Bases and Salts

• A Hydrogen atom consists of a single proton and a single electron (no neutron)
• Thus, an H⁺ ion is just a proton
• Acids are often referred to as "proton donors"

Different types of acids can ionize to release one or more protons

• A monoprotic acid releases a single proton when it ionizes (e.g. hydrochloric acid):

• A diprotic acid can release two protons when it ionizes (e.g. sulfuric acid):

• For sulfuric acid, the first ionization is complete (as indicated by the single arrow), therefore it is a strong electrolyte
• However, only some of the molecules of HSO₄^- undergo a second ionization. Thus, the deprotonization of HSO₄^-, and the protonization of SO₄^2- are significant reactions (as indicated by the double arrows)
• Aqueous solutions of sulfuric acid will therefore contain some mixture of protons (H⁺), HSO₄^- and SO₄^2-ions

• A common example of a base is the hydroxide ion (OH^-):

• Some of the most common bases are metal hydroxides (e.g. NaOH, KOH, Ca(OH)₂)
• These are ionic compounds, that when dissolved in H₂O release the metal ion and one or more hydroxide (OH^-) ions

Other compounds can react with H₂O in such a way that they are considered bases (even though they do not directly contribute a OH^- ion)

• Ammonia (NH₃) reacts chemically with a H₂O. It has a high affinity for the proton that can be obtained from a water molecule. This leaves a hydroxide ion (OH^-) left over in solution:

• Ammonia has "accepted a proton" from the water molecule, and the concentration of OH^- ions has increased in solution, thus, ammonia is a base
• Note that the double arrows indicate that only some of the ammonia molecules will react with water to accept a proton. Thus, ammonia is a weak electrolyte.

• Acids and bases that ionize completely in solution are strong electrolytes, and are therefore known as strong acids or strong bases
• Likewise, acids and bases that only partially ionize in solution are weak electrolytes, and are known as weak acids or weak bases
• If a chemical reaction depends upon the concentration of H⁺ ions, then strong acids will be more chemically reactive than weak acids
• However, the anion that is also released in the ionization of an acid can also be reactive. If a weak acid (e.g. HF) releases an anion that is highly reactive (e.g. F-), then the weak acid can also be chemically highly reactive

Some strong acids and bases:

Observations about acids and bases:

1. The commonly used acids, hydrochloric, nitric and sulfuric, are all strong acids
2. Several of the strong acids are a combination of hydrogen and a halogen (the exception is HF, which is a weak acid)
3. There are not a lot of strong acids, most acids are weak acids
4. There are not a lot of strong bases; the strong bases are metal hydroxides (group 1A and heavy group 2A metals)
5. Ammonia (NH₃) is a weak base

Based on the above discussion, here is a flow chart to help you decide if a compound is a strong or weak electrolyte (or a nonelectrolyte):

When an acid solution and a base solution are mixed, a neutralization reaction occurs.

• In general, a neutralization reaction between an acid and a metal hydroxide (strong base) produces water and a salt
• The term salt has come to mean any ionic compound whose cation comes from a base and whose anion comes from an acid

• Example: aqueous hydrochloric acid mixed with aqueous sodium hydroxide