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By zagambhatti Dec 04, 2013 704 Words
Objective:
Learning how to Prepare Buffers of Various pH levels and Preparation of Acetate Buffer. Introduction
A buffer is a solution having the capacity to resist changes in pH levels. Mostly a buffer consists of a weak acid and a salt of strong base or a weak base and a conjugate salt of strong acid e.g. acetate buffer is the most common buffer in which equimolar mixture of acetic acid and sodium acetate solution is used. CH3COOH CH3COO - + H+

CH3COONa CH3COO - + Na+
Buffers are divided into 2 parts on the basis of their nature. Acidic Buffer
Basic Buffer
The most common buffers are Acetate buffer, Phosphate buffer, Citrate Buffer and Tris-HCl. The Limit up to which buffer can resist changes in pH is called Buffer Capacity. Apparatus
100ml beaker
Digital balance
Stirrer
Scientific Calculator
Chemicals
Sodium Acetate
Acetic Acid
Chemical Equation
CH3COOH CH3COO - + H+
CH3COONa CH3COO - + Na+
Procedure
An Acetate Buffer solution of 0.1M solution in 1 Litre of pH = 5.24 was prepared in the following steps. 1. 0.1M solution of CH3COONa was prepared in a 1000ml flask. 2. 0.1M solution of CH3COOH was prepared in a 1000ml flask.

3. 750ml solution of 0.1M of CH3COONa was taken in a 1000ml flask and 250ml of CH3COOH was added to it. 4. The solution was mixed well.
5. Its pH was tested and verified with pH meter.
Observations:
Henderson-Hansselbach Equation
pH = pKa + log
Dissociation Constant of CH3COOH
Ka =
-log Ka = log [H+] – log
pKa = pH – log
pH = pKa + log
e.g. if we want to make a solution of 0.1M and 5.76pH , then we know the pKa value of CH3COOH is 4.76 in pKa table, So, putting all values in formula we get. 5.76 = 4.76 + log
=> 5.76-4.76 = log
=> 1 = log
=> (-log)(1) = (-log)(log)
=> 10 =
=> = =
=> [CH3COONa] : [CH3COOH] = 10 : 1
And if we want to make 0.1M solution in 1 Litre, then
x 1000 = x 1000
=> x 1000 = x 1000
=> 901.1ml CH3COONa = 90.9ml CH3COOH
Now if we mix this amount of Strong Acid and Conjugate base of strong acid then we will get a Buffer solution of 0.1 Molar solution of 5.76pH in 1 Litre.

Calculations
Preparation of Acetate buffer of 0.1M of 5.24 pH level in 1 litre solution. 5.24 = 4.76 + log
=> 5.24 - 4.76 = log
=> 0.48 = log
=> (-log)(0.48) = (-log)(log)
=> 3 =
=> = =
=> [CH3COONa] : [CH3COOH] = 3 : 1
750ml of 0.1M CH3COONa = 250ml of 0.1M CH3COOH
So, if we mix this amount of Strong Acid and Conjugate base of strong acid then we will get a Buffer solution of 5.76pH in 1 Litre. Now the question is how to make 0.1M of CH3COONa and CH3COOH respectively? For this purpose we followed the following steps,

We made 0.1M solution of CH3COONa and CH3COOH.
For CH3COONa
Atomic weight of CH3COONa = 82
1 Molar solution = 82/1000
Means 82gm CH3COONa taken and dissolved in a 1000ml beaker in such a way that the volume raise up to 1000ml. For 0.1M we have,
0.1M = (82/10) / 1000 = 8.2 / 1000
Means 8.2gm CH3COONa taken and dissolved in a 1000ml beaker in such a way that the volume raise up to 1000ml. For CH3COOH
C1V1 = C2V2
C1 = 17.5m stock solution available from Market.
V1 = ?
C2 = 0.1M
V2 = 1000ml
Now,
V1 = =
V1 = 5.71ml
Which means 5.71ml of 17.5M of Stock solution available in Market was taken in a 1000ml flask and its volume was raised up to 1000ml. SO now,
Take 750ml of CH3COONa and 250ml CH3COOH from the above mentioned solutions of CH3COONa and CH3COOH having 0.1 as Molarity. Results
The pH of Acetate buffer was tested with pH meter and was verified as having 5.24 pH value. Discussion
Buffer solutions are very important in every life specially if we have to deal with enzymatic activity in Laboratory because the normal pH of Human body is 7.4 on which an enzyme can be on its maximum efficiency. So in order to study enzymes properly we will have to make a buffer of 7.4 pH so that enzyme does not denatures or show less activity.

Similarly while dealing will blood or studying the Cell cytoplasm etc we will also make a buffer of ph 7.4 because on this pH a normal human cell can perform its function. Any change in pH level can make cell dead or affects cell adversely.

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