Acids in Solution

The properties of acids only show up when water is present. The terms concentrated and dilute refer to the amount of water present. Concentrated solutions have more acid particles present in a certain volume of the solution than dilute solutions. Some acids, such as concentrated nitric acid, are very dangerous. Adding water to a concentrated acid makes it more dilute but even dilute solutions of strong acids need to be handled with caution.

Aqueous solutions that are acidic usually contain lots of H⁺ ions (hydrogen ions).

The symbol H⁺_(aq) represents hydrogen ions dissolved in water and the greater the concentration of hydrogen ions dissolved in the water the lower the pH.

The bottles of dilute nitric acid and concentrated nitric acid show hazard warning symbols. Click on the picture to see the precautions to be taken when handling these solutions.

The complete ionisation of hydrochloric acid.
The animation shows hydrochloric acid molecules in water completely changing into H⁺ and Cl^-.

Hydrochloric acid molecules break up into hydrogen ions and chloride ions. Because of this, hydrochloric acid is classified as a strong acid. A strong acid is completely ionised in aqueous solution.

Hydrochloric acid splits up (ionises) completely when dissolved in water.

The partial ionisation of ethanoic acid.
The animation shows ethanoic acid molecules in water, only one of them changes into CH₃COO^- and H⁺ ions.

Ethanoic acid molecules only form a few ethanoate ions and hydrogen ions. Because of this, ethanoic acid is classed as a weak acid. A weak acid is only partially ionised in aqueous solution.

For a given concentration, a strong acid will produce a lot more H⁺ ions in solution than a weak acid and so it will have a lower pH. Strong acids usually have much faster reactions than weak acids of the same concentration.

Ethanoic acid only partly splits up (ionises) in solution