determination of strength of a strong acid by pH-metric titration

1. Determination of strength of strong
acid by pH-metric titration

2. AIM
To estimate the amount of acid present in given solution by pH metric method.

3. • pH –
The negative logarithm of the H ion activity
pH = -log[H+]
• Strong Acid or Base :
– The acids or bases that completely dissociated into their ions
when the acids or bases that completely dissociated into their
ions when it is in aqueous solution.
• Weak Acid or Base :
– The acids or bases that partially dissociated into their ions when
it is in aqueous solution
PRINCIPLE AND THEORY

4. • Strong acid - HCl
• Strong base – NaOH
• Neutralization reaction

6. • Initial pH is depend on the initial concentration of
strong acid
• As strong base is added the pH is increase slowly.
• The pH of the solution before the equivalence point
increase quickly.
• At the equivalent point number of moles of acid is
equal to the number of moles of acid based on
stochiometrically.
• The pH after the equivalent point is determined by
the concentration of the excess NaOH.

10. Image credit:
https://community.asdlib.org/imageandvideoexchangeforum/2013/07/31/ph-
electrode/

14. The
combination
electrode

16. Working of glass electrode...

17. EXPERIMENT
PROCEDURE

18. Solution of HCl and
NaOH is given.
Standardise NaOH.
Calibrate pH meter using
Buffer Solution.

19. WHAT IS THE
PURPOSE OF
CALIBRATION
?
WHY DO WE
USE BUFFER
SOLUTION
TO
CALIBRATE
pH METER ?

20. Transfer 40 mL of made up HCl solution into a 100 mL beaker.
Clean the electrode with distilled water and keep it into HCl solution.
Connect to pH meter.
Fill the Burette with NaOH solution.
Add 0.5 mL of NaOH solution to HCl solution.
On each addition record the pH.
During determination, the solution should be under stirring.
Until there is a sudden change in pH, the values are noted.
Graph of pH Vs Volume of NaOH plotted.

21. S.No. Volume of
NaOH (mL)
pH ∆pH ∆V ∆pH/∆V
1 0 1.25 - - -
2 0.5 1.27 0.02 0.5 0.04
3 1 1.28 0.01 0.5 0.02
4 1.5 1.31 0.03 0.5 0.06
5 2 1.37 0.06 0.5 0.12
17 8 3.72 0.30 0.5 0.60
18 8.5 11.30 7.58 0.5 15.6
19 9 11.44 0.14 0.5 0.28
30 14.5 11.99 0.05 0.5 0.1
31 15 12.02 0.03 0.5 0.06
∆pH=pH2 –pH1
∆V= V2 – V1

22. Sigmodial Graph Differential Graph

23. Y axis 1, 8, 3.72
Y axis 1, 8.5,
11.3
pH
Volume of NaOH (in mL)
Y axis 2, 8.5,
15.16
∆pH/∆V
Volume of NaOH (in mL)
GRAPH

24. Calculation
Volume of NaOH solution ,V1 = 8.5 mL
Normality of NaOH solution ,N1 = 0.1 N
Volume of HCl solution,V2 = 20 mL
Normality of HCl solution ,N2 = 0.0425 N
Amount of HCl present in 1 litre = Normality x Eq. Wt
= 0.0425 x 36.45
= 1.5491 g/L
Amount of HCl present in the = (1.5491 x 100)/1000
given solution (i.e., 100ml) = 0.1549 g

25. • pH Meter is very crucial in Agriculture industry for soil evaluation.
• To know the pH of buffer solution
• To measure the pH of rainwater
• It becomes mandatory for chemical and pharmaceutical industries
• pH meter is used in brewing industry.
• It is also used in jam and jelly manufacturing
• It becomes a significant factor in the production of detergents.
• It is used for monitoring water in swimming pools
• pH meter helps in analyzing the exact pH value of chemical substances and
food grade products, thus ensuring high levels of safety and quality.

26. CB.SC.I5CHE18019
CB.SC.I5CHE18020
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