Preparation of the buffer solutions, titration of amino acid

and there buffering capacity

Tahani Alshehri Tmalshehri@ksu.edu.sa

2009

Objective

• To Study the nature of the buffers

Introduction & principle

• Buffer solution – a solution which resist the changes in pH upon

addition of small amounts of acid or base, or upon dilution

– Is a the weak acid and its salt in strong base in a buffer a solution .

Acidic buffer solutions

• An acidic buffer solution is simply one which has a pH less than 7.

• Acidic buffer solutions are commonly made from a weak acid and one of its salts - often a sodium salt.

Alkaline buffer solutions

• An alkaline buffer solution has a pH greater than 7.

• Alkaline buffer solutions are commonly made from a weak base and one of its salts.

?

• ethanoic acid and sodium ethanoate• ammonia solution and ammonium chloride

solution

Acidic buffer solutions

• We'll take a mixture of acetic acid and sodium acetate as typical.

• acetic acid is a weak acid

• Buffers are main important in regulating the pH of the body fluids and tissues within limits consistants with life and normal function

• Many body chemical reaction including those catalyzed by enzyme require pH control which is provided by buffers

• Mammalian tissue in the resting state have a pH of about 7.4

Henderson–Hasselbalch equationThe pH of the buffer is given by Henderson–Hasselbalch equation

Which for practical purposes , becomes

Here, pKa is − log(Ka) where Ka is the acid dissociation constantof the acid

How do buffer solutions work?

• A buffer solution has to contain compounds which will remove any hydrogen ions or hydroxide ions that you might add to it - otherwise the pH will change.

• Acidic and alkaline buffer solutions achieve this in different ways.