Acid/Base (Neutralization) Reactions

Acid-base reactions are ubiquitous. In aqueous solutions acids increase the hydrogen ion (H+) concentration. On the other hand bases increase the hydroxide ion (OH-) concentration. When an acid and a base react in an aqueous solution the H+ and OH- ions combine to form water. These ions thus "neutralize" one another:

Most acids have the general formula HA, where A- is an anion and most bases have the form BOH, where B+ is an appropriate cation. Acids and bases can be grouped into two general types: strong and weak acids and bases. The difference between the two is straightforward: a strong acid in a water solution decomposes 100% into a proton (H+) and anion (A-)

On the other hand most weak acids decompose significantly less than 100% in a water solution:


In other words most weak acid molecules stay intact in water. Similar chemical equations hold for strong and weak bases.

There are only a few weak acids and bases, they are:

 Strong Acids

 Strong Bases

HCl (hydrochloric acid)

HNO3 (nitric acid)

HClO4 (perchloric acid)

H2SO4 (sulfuric acid)

NaOH (sodium hydroxide)

KOH (potassium hydroxide)

Ca(OH)2 (calcium hydroxide)

All other acids and bases are weak. A weak acid results from any anion. Examples are given below


Weak Acid

F- (fluoride)

Br- (bromide)

I- (iodide)

HCO3- (bicarbonate)

C2H3O2- (acetate)

MnO4- (permanganate)

PO4-3 (phosphate)

CrO4-2 (chromate)

CN- (cyanide)

NO2- (nitrite)

SO3-2 (sulfite)

HF (hydrofluoric acid)

HBr (hydrobromic acid)

HI (hydroiodic acid)

H2CO3 (carbonic acid)

HC2H3O2 (acetic acid)

HMnO4 (permanganic acid)

H3PO4 (phosphoric acid)

H2CrO4 (chromic acid)

HCN (hydrocyanic acid)

HNO2 (nitrous acid)

H2SO3 (sulfurous acid)

In a typical acid/base reaction the acid and base react to form a salt and water e.g., hydrocyanic acid and sodium hydroxide:

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C101 Class Notes
Prof. N. De Leon