mass
amount
molar mass
concentration
solution volume
gas volume
molar gas volume
Avogadro
constant, L
number of
entities, N
P3. ACID-BASE NEUTRALIZATION REACTIONS
P3.1 Background
For thousands of years people have known that vinegar, lemon juice and many other foods taste sour. Not until a few hundred years ago, however, was it discovered why those taste sour - because they are all acids. Acid, in fact, comes from the Latin term acere, meaning “sour”.
In the late c.17th, Robert Boyle characterized acids by their sourness and attempted to explain this property by suggesting that atoms of acids were coated with spikes. Human tongues have sense receptors that respond specifically to sourness, but we appear not to have any specific sensitivity to bases.
A substance which is acidic has a sour taste, is generally corrosive above certain concentrations, and changes the colour of indicators. It also reacts with carbonates to produce carbon dioxide and with moderately reactive metals to produce hydrogen gas.
Similarly, substances described as alkaline are known for their soapy feel, which is usually attributed to their ability to hydrolyse the proteins in the skin, and for their ability to neutralize the properties of acidic substances.
During the last 130 years or so, a number of theories on acids and bases have been developed and they are described briefly in the table opposite (pdf) along with some earlier generalizations. In 1884 Svante Arrhenius was the first to propose a meaningful acid-base theory based on ionization.
It was Søren PL Sørensen, working as a biochemist for Carlsberg, who introduced the pH scale in 1909 as a more convenient method of expressing the degree of acidity or alkalinity of an aqueous solution. His logarithmic pH scale, running typically from 0-14, was a lot less cumbersome when comparing the wide range of hydrogen ion concentrations observed across the myriad of acidic and alkaline mixtures encountered daily in laboratories worldwide.