P h metric titration

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

5. 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.

6. INSTRUMENTATION

7. Apparatus Required Standardized solution of NaOH, about 0.100 N 100 mL standard flasks 100 mL beaker Burette Pipette Glass rod pH meter pH electrode Buffer solutions

8. Experimental Set-up

9. pH Electrode The pH electrode is a combination electrode with a glass electrode and a reference Ag/AgCl electrode. The glass electrode has a bulb at the bottom filled with HCl, and an internal Ag/AgCl reference electrode. KCl is the supporting electrolyte for the reference electrode. The porous wick acts as the salt bridge. The pH is measured by the pH sensitive glass membrane of the bulb. Image credit: https://community.asdlib.org/imageandvideoexchangeforum/2013/07/31/ph-electrode/

10. Working principle  of  pH metry  

11. Introduction.. The history of measuring acidity of liquids electrically began in 1906 when Max  Cremer in his studies of liquid interfaces (interaction between liquid and solid ) discovered that the interface between liquids could be studied by blowing a thin bubble of glass  and placing one liquid inside it and another outside .it created an electric potential that could be measured . This idea was taken further by Fritz Haber (who invented the synthesis of ammonia and artificial fertiliser ) and Zygmunt Klemsiewicz  who discovered that the glass bulb (which he named  glass electrode ) could be used to measure hydrogen ion activity and that this followed a logarithmic function. The danish biochemist soren sorenson then invented the PH scale in 1909

12. Why  is the pH scale logarithm ??? the possible range of hydrogen (H+) and hydroxide (OH-) ion activity can span many orders of magnitude. In order to easily manage and represent the wide range of ion activities, a logarithmic pH scale is used.   So a change on the  pH scale of 1  unit  indicates that hydrogen ion activity differs by an order of magnitude 10.  Due to the logarthmic nature -we don’t average the pH values and report –instead we report the median value or provide a range of pH values observed .

13. The combination electrode 

14. Fundamentally, a pH  metery setup  consists of a voltmeter attached to a pH-responsive electrode and a reference (unvarying) electrode. The pH-responsive electrode is usually glass , and the reference is usually a silver –silver chloride electrode, although a mercury –mercurous chloride (calomel) electrode is sometimes used.  When the two electrodes are immersed in a solution, they act as a battery . The glass electrode develops an electric potential  (charge) that is directly related to the hydrogen-ion activity in the solution (59.2 millivolts per pH unit at 25 °C [77 °F]), and the voltmeter measures the potential difference between the glass and reference electrodes. By the nernst equation .

15. Working  of glass electrode...

16. EXPERIMENT PROCEDURE

17. S.No. Volume of NaOH (mL) pH ∆pH ∆V ∆pH/∆V 1 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 =pH 2 –pH 1 ∆V= V 2 – V 1

18. Sigmodial Graph Differential Graph

19. GRAPH

20. Calculation Volume of NaOH solution ,V 1 = 8.5 mL Normality of NaOH solution ,N 1 = 0.1 N Volume of HCl solution,V 2 = 20 mL Normality of HCl solution ,N 2 = 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  

21. 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.

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