M5 Acids, Bases and Buffers Q&A
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Explain what is meant by a buffer, giving an example, and describe how it is prepared.
• A buffer is a mixture which minimises pH changes when small amounts of acid or alkali are added • It is a mixture of a weak acid (e.g. propanoic acid, CH3CH2COOH) and its salt (e.g. sodium propanoate, CH3CH2COONa) • It is prepared by mixing a small amount of a strong base (e.g. NaOH) with an excess of the weak acid; this produces the salt but also leaves some acid remaining
Explain how a buffer works.
How is a suitable indicator chosen for a particular acid-base titration?
• The colour change (end-point) of the indicator must lie within the pH range of equivalence (equivalence point) (quote this range from the pH curve – the vertical section) • The colour change must also be sharp and distinct