Acid-base titrations

Acid-base reactions involve the transfer of protons from acid to bases. Acids are proton donors and bases are proton acceptors. A ‘strong’ acid refers to an acid that readily donates protons. Some examples of strong acids include HNO₃, H₂SO₄ and HCl. In contrast, a ‘weak acid’ refers to one that does not readily donate protons. Examples include CH₃COOH. Similarly, ‘strong’ bases refer to bases that readily accept protons whereas weak bases refer to bases which do not readily accept protons.

In acid-base titrations, indicators are often used to help identify the equivalence point of reactions. Indicators are usually weak acids that exhibit a colour change when there is a change in the hydrogen ion concentration of a solution. Examples of indicators include phenolphthalein and methyl orange.

Conjugate acid-base pairs are pairs of molecules that differ by 1 H⁺. Examples of conjugate pairs include Cl^–/HCl and HSO₄^–/H₂SO₄.

pH

pH is a measure of acidity; the concentration of H₃O⁺ ions in a solution.

(pH is further discussed in unit 4).

For titration curves, a sharp end point is desired to accurately determine when a reaction has reached its equivalence point. Hence, reactions involving strong acids and strong bases are ideal to provide a sharp end point and those involving weak acids/bases need to undergo back titration. Reactions involving weak acids with weak bases produce a very ‘flat’ curve which greatly affects the accuracy of results obtained.

See Also

pH