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Buffer solutions consist of:
There are two types of buffer solution the acid buffer solution and the base buffer solution, the difference between them is the pH at which they buffer at; they both though rely upon the point of half neutralisation and the small changes in pH that occur about this point . This effect can be demonstarted by pH titration curves for both acid and base buffers.
An acid buffer is one that stabalises the solution at a pH below 7. It usually consists of a weak acid and a salt of its conjugate base. eg. acetic acid CH3COOH and sodium acetate NaOOCH3.
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Left is a pH titration curve of a weak acid and a strong base. The part of the graph at which the pH alters slowly is below 7. This part of the graph is the pH range at which the solution will buffer within. |
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A base buffer is one that stabalises the solution at a pH above 7. It usually consists of a weak base sucha as ammonia NH3 and a salt of its conjugate base such as amonium chloride NH4Cl.
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Left is a pH titration curve of a weak base and a strong acid. The part of the graph at which the pH alters slowly is above 7. This part of the graph is the pH range which the solution will buffer within. |
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As we will discover a solution can be made to buffer at any pH range required simply by selecting an acid or base with the right pKa. Fine tuning of the pH range can be achieved by altering the concentartion of the acid or base.
To see how the conjugate acid and bases work together to minimise pH changes in a buffer solution go to the How do buffer solutions work page.