Learn about the potentiometric titration of strong acid vs strong base through a laboratory experiment or practical.
Aim:
To determine the strength of strong acid using a strong base by potentiometry.
Requirements:
Glasswares: Burette, burette stand, conical flask, volumetric pipette, beaker, volumetric flask, funnel, glass rod, and wash bottle, etc.
Chemicals: LR grade sodium hydroxide (NaOH), sulphuric acid (H2SO4), potassium hydrogen phthalate (KHP), anhydrous sodium carbonate (Na2CO3), and phenolphthalein indicator, etc.
Apparatus: Digital/analytical balance, and ultrasonicator, potentiometer, and magnetic stirrer.
Principle:
In principle, determining the pH of a solution is easy since it is based on measuring the potential of a hydrogen electrode immersed in the sample solution.
Potentiometry is a type of electrochemical measurement. A strong acid is H2So4, while a strong base is NaOH. H2So4is directly titrated with sodium hydroxide to determine its strength. There is no indicator is required since the endpoint of the reaction can be detected by a sharp change in potential across the electrodes.
Preparation of reagents and solutions:
Click here to get the procedure of preparation and standardization of 01 M sodium hydroxide.
Click here to get the procedure of preparation and standardization of 01 M sulphuric acid solution.
Titration procedure:
- All glassware should be cleaned and dried according to standard laboratory procedures.
- Before filling the burette for the titration, rinse it with distilled water and then pre-rinse it with a portion of the titrant solution. Pre-rinsing is required to make sure that all solution in the burette is the desired solution, not a contaminated or diluted solution.
- Take the unknown stock solution of titrant in a clean and dry beaker then fill the burette using the funnel.
- Remove air bubbles from the burette and adjust the reading to zero.
- Switch ON the potentiometer and calibrate the electrodes with pH 04.00, 07.00, and 09.20 standard buffer solutions.
- Once it is calibrated, rinse the electrode with distilled water.
- Take 50.00 ml of sulphuric acid, pour it to a beaker
- Properly place the beaker on a stirrer and immerse both the electrodes and set the burette properly on the beaker.
- Note down the initial reading of the sample i.e. e.m.f. in millivolts (mV).
- Turn on the stirrer and add 01.00 ml standardized NaOH solution from the burette at a time, properly record the readings in mV.
- Continue the titration process until the endpoint is reached.
- The actual endpoint of the titration is indicated by a sharp increase in e.m.f.
- Even after you've reached the endpoint, take a few more readings.
- Plot the graph and calculate the strength of sulphuric acid.
Calculations:
M1V1= M2V2
M2 = V1 M1 / V2
Where,
M1 is the molarity of sodium hydroxide
V1 is the volume of sodium hydroxide
M2 is the molarity of sulphuric acid
V2 is the volume of sulphuric acid
Result:
The strength of sulphuric acid was found to be___ by plotting the normal 1st and 2nd derivative curves.
Commonly asked question on acid-base titration are as follows.
What is potentiometric acid-base titration?
The potentiometric titration technique is similar to the direct titration of a redox reaction. It's a useful method for characterizing an acid. Instead of using an indicator, the potential across the analyte, which is usually an electrolyte solution, is measured.
Which indicator can be used in the titration of strong acid and strong base?
Phenolphthalein indicator is most commonly used in the titration of strong acid and strong base which is one of the most suitable indicators for acid-base titration.
Which is the example titration of a strong acid with a strong base?
The titration of hydrochloric acid (HCL) in the form of strong acid and sodium hydroxide (NaOH) as the strong base is an example of titration of a strong acid with a strong base.
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