Acids, Bases and Salts

Acids and Bases

Acid A substance which ionizes to form H+ (H+ is a product).

Examples

HNO3(aq) H+(aq) + NO3-(aq)

HCl(aq) H+(aq) + Cl-(aq)

Base A substance that accepts (reacts with) H+.

Examples

OH-(aq) + H+(aq) H2O(l)

NH3(aq) + H+(aq) NH4+(aq)

Note that to obtain hydroxide ions (OH-) we start with an ionic compound that dissolves in water to form hydroxide ions, such as the alkali metal hydroxides, LiOH, NaOH, KOH, RbOH, etc.

Since both acids and bases dissolve in water to form ions, they are both electrolytes. However, most acids and bases do not completely dissociate to form ions, those that do are called strong acids or strong bases.

 

The list of strong acids and bases is given in your book in table 4.1 and below. You will be expected to memorize this list.

Strong Acids  

Perchloric acid

HClO4

Chloric acid

HClO3

Hydrochloric acid

HCl

Hydrobromic acid

HBr

Hydroiodic acid

HI

Nitric acid

HNO3

Sulfuric acid

H2SO4

Strong Bases  

Group 1A metal hydroxides

LiOH, NaOH, KOH, RbOH, CsOH

Heavy group 2A metal hydroxides

Ca(OH)2, Sr(OH)2, Ba(OH)2

Unless told otherwise we will assume that all other acids and bases are weak.

How can I recognize an acid?

We expect an acid when hydrogen combines with either a non-metal or a polyatomic anion.

Examples

H2S, H3PO4, HF, HCl, HClO, HC2H3O2 etc.

How can I recognize a base?

At the moment we will only concern ourselves with two types of bases:

Examples

KOH, LiOH, NH3, Ca(OH)2, NH4OH, etc.

Neutralization Reactions and Salts

Neutralization Reaction A reaction between an acid and a base.

If the base is a metal hydroxide then one of the products is water while the other product is a salt.

Example

HNO3(aq) H+(aq) + NO3-(aq)

NaOH(aq) OH-(aq) + Na+(aq)

When we combine HCl and NaOH solutions the H+ and OH- ions combine to form water and a salt solution:

HNO3(aq) + NaOH(aq) H2O(l) + NaNO3(aq)

(acid) + (base) (water) + (salt)

Salt Any ionic compound whose anion comes from an acid and whose cation comes from a base.