Acids and Bases

We began on a new topic Acids and Bases. For me, it was a very challenging topic as I had difficulty memorising the chemical names and formulas. It took a lot of revision to grasp the concept.

To begin, an acid is a substance which produces hydrogen ions as the only positive ions when it is dissolved in water. Some examples of strong acids are Hydrochloric acid, Nitric acid and Sulfuric acid. On the other hand, some examples of weak acids are ethanoic acid and citric acid. The strength of an acid depends on its degree of dissociation / ionisation in water to form hydrogen ions.

Strong Acids
Strong acids are acids that ionise / dissociate completely in water to produce hydrogen ions (H+).
There are no molecules left.
The properties and reactions of acids are due to these hydrogen ions.

Weak Acids
A weak acid is one that ionises / dissociates incompletely / partially in water to produce few hydrogen ions (H+).
Most of the acid molecules remain as molecules.

Concentration
A concentrated acid is one in which the proportion of acid to water is very high.
A diluted acid is one in which the proportion of acid to water is low.
The concentration of an acid does not affect the strangth of an acid.

Importance of water for acidity
Pure acids exist as molecules instead of ions.
Pure acids do not behave as acids as the properties of acids are due to the presence of hydrogen ions.
When acids are mixed with water, ionisation of acids occurs, and hydrogen ions are produced. Therefore, acids can only behave as acids when they are dissolved in water.

Properties of Acids
Acids have a sour taste.
Acids dissolve in water to form colourless solutions which conduct electricity.
Acids turn blue litmus red.

Reactions
Acids react with metals, carbonates & bases
Acids react with metals to produce salt and hydrogen
(However, metals less reactive than hydrogen is not reactive enough to react with acids.)
Acids react with carbonates to produce salt, carbon dioxide and water
Acids react with bases to produce salt and water

pH
pH values depend on the concentration of acid/base and degree of dissociation. The use of pH in measuring the strength of an acid is limited since its value changes with concentration.