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Pka value of weak acid experiment by titrations method

The document details an experiment to determine the pKa value of a weak acid through titration with a strong base and to assess the maximum buffer capacity of acetic acid and its salt. It introduces concepts of buffer capacity, potentiometry, and provides procedures for measuring pH using various methods and a potentiometer. The results indicate the maximum buffer capacity and highlight the importance of buffers in maintaining pH in pharmaceutical solutions and biological systems.

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~By. Pankaja p Pka value of weak acid
AIM : ■ TO DETERMINE Pka VALUE OF WEAK ACID BY TITRATING IT AGAINST STRONG BASE USING POTENTIOMETRE OR ■ To determine the maximum buffer capacity of weak acid (Acetic acid) and its salt of strong base.
OBJECTIVES 1) To learn concept of buffer capacity and its utility. 2) To develop concept of potentiometry and handling of potentiomter.
Pka —》Dissociation constant. Buffer consists —》weak acid and weak base Note : weak acid don’t dissociate completely
DEFINATION:- Buffer " Buffers are mixtures of compound that by their presence in the solution resists change in the PH upon the addition of small quantities of acid or alkali. "
BUFFER CAPACITY "The buffer capacity of a buffer solution is a measure of magnitude of its resistance to change in PH on an addition of an acid or a base."
Buffer capacity is represented by= B (Beta) Also referred as:‐ 1) Buffer index 2) Buffer value 3) Buffer efficiency 4) Buffer coefficient
PH of Body fluids = 1-8 PH of Blood = 7.4 PH of stomach = 1-3 PH of Intestinal fluid = 6-7 PH of skin = 6-6.5
NECESSITY OF BUFFER ■ If solution come in contact with air , it will absorb co2 and become acidic. ■ If solution is stored in glass bottle, alkaline impurities from glass may alter the PH. ● Due to these reasons , pharmaceutical solutions are buffered as the buffer solution are capable of maintaining PH at some constant value when even small amount acid or base are added.
Determination of PH ■ Electromeric method . - glass electrode or calomel electrode. ■ Calorimetric method. a) by PH paper b) by standard buffer solution and different ph range
POTENTIOMETRE Potentiometre is a device to determine the PH Potential it is equivalent of strong acid or strong base that should bring about a net change in the PH .
APPLICATION OF BUFFERS 1) In biological systems :-pH of Blood = 7.4 a) Primary buffers :- Present in plasma. b) Secondary Buffers :-Present in Erythrocytes 2) pharmaceutical preparation ( injections) – opthlamic preparation –ointments and creams
Henderson- Hasselbalch equation It gives PH of buffer solution of a weak acid and it’s salt. for acid PH = Pka + [ salt ]/ [ acid] For base POH= Pkb + [ salt ]/[ base ]
Requirements Chemicals: - distilled water, sodium hydroxide, acetic acid, buffer solution, phenolphthalein. Apparatus: -potentiometer, beakers, burette, pipette, funnel, clamp etc.
PROCEDURE 1) Switch on the pH meter and allow it to stabilize for 10 minute. 2) Wash the electrode in distilled water and wipe with clean and dry tissue paper. 3) Dip the electrode in the buffer solution of known pH ( 4, 7,9). If the pH is different from standard one then adjust the pH meter to give exact pH reading. Now pH meter is standardize and ready to use.|
PROCEDURE 4) Take 20ml of 0.4M acetic acid in a beaker and pH is recorded+10ml of 0.2N NaOH and pH is again recorded. 5) When there is sudden increase in pH note the reading and continue for 4-5 readings. 6) Plot a graph of β (Buffer capacity) against pH.
Formula B=dB/dPH B Is small increment in gram equivalent Per liter strong acid or base added to solution to produce PH change PH . Pharmaceutical preparation should have a low buffer capacity.
dB = 2/25× V 1)For V= 25 dB = 2/25×V = 2/25×25 = 2 2) For V = 26 dB = 2/25×26 = 2.08 Calculation
B= dB/dPH 1) dB = 2.08 dPH = 0.3 B= 2.08/0.3 = 6.933 2) dB =2.16 dPH = 0.2 B= 2.16/0.2 = 0.8
Amount of 0.4N NAOH (ml) volume in beaker (ml) PH dPH dB B=dB/dPH 0 25 3.5 0 2 0 1 26 3.8 0.3 2.08 6.933 2 27 4 0.2 2.16 10.8 3 28 4.2 0.2 2.24 11.2 4 29 4.5 0.3 2.32 7.33 5 30 4.7 0.2 2.4 12 6 31 4.9 0.2 2.48 12.4 7 32 5.4 0.5 2.56 5.12 8 33 5.8 0.4 2.64 6.6 9 34 6.5 0.7 2.72 3.88 10 35 9.3 2.8 2.8 0.1 11 36 9.8 0.5 2.88 0.576
0 6.933 10.8 11.2 7.33 12 12.4 5.12 6.6 3.88 0.1 0.576 0 2 4 6 8 10 12 14 3.5 3.8 4 4.2 4.5 4.7 4.9 5.4 5.8 6.5 9.3 9.8 B=dB/dPH B=dB/dPH
RESULT The maximum buffer capacity of weak acid and it’s salt of strong base and As it’s half neutralization point at PH 9.3
Pka value of weak acid experiment by titrations method
Pka value of weak acid experiment by titrations method