Showing posts with label Potentiometric titration. Show all posts
Showing posts with label Potentiometric titration. Show all posts

Monday, August 30, 2021

Potentiometric titration of strong acid against strong base

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.
potentiometric titration of strong acid vs strong base

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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Friday, July 30, 2021

Advantages and disadvantages of potentiometric titration

Potentiometric titration includes the determination of the potential of a sample as a function of titrant volume, it has many advantages as well as some disadvantages, let's check them.

Potentiometric titration is used to determine electrical potential changes while a neutralizing agent is added to a sample solution. Potentiometric titration is a technique that is like the direct titration of a redox reaction. There are four types of potentiometric titration such as acid-base titration, redox titration, complexometric titration, and precipitation titration.

This includes the determination and recording of the cell potential in the unit of millivolt or pH after each titrant addition. It uses two types of electrodes are used indicator electrode and a reference electrode. The metal ion indicator, glass electrode, calomel electrode, silver chloride electrode, and hydrogen electrode are commonly used in the potentiometric titration. To perform the titration several apparatus are required such as burette, conical flask, pipette, volumetric flask, funnel, stand, beaker, and wash bottle, etc.

Here are mentioned some of the advantages and disadvantages of potentiometric titration.

Advantages of potentiometric titration:

  • The major advantage of potentiometric titration is that it is a direct titration in which an indicator is not required to determine the endpoint or equivalence point of the reaction.
  • Potentiometric titration is used as an automated system with more sample processing capacity that is applied in different fields.
  • It can also perform in a sample containing a small amount of analyte whose concentration needs to be determined.
  • The advantage of using this titration method is that it is an economical method.
  • The results of this titration are accurate and sharp since the equivalence point is not estimated through a color indicator.
  • This type of titration is functional if the solutions are turbulent, fluorescent, and colored where the endpoint obtained by the indicator is masked.
  • Automated endpoints give accuracy compared to manual titration.

Disadvantages of potentiometric titration:

  • The major disadvantage of potentiometric titration is that they are very sensitive to pH.
  • Potentiometric titration takes a longer time than titration with the indicator.
  • Errors can occur when preparing solutions or by any contamination.
  • If the electrode is exposed to air, the pH reading may be different.
  • Need for exactly known concentrations of solutions.
  • We need to calibrate frequently.
  • It is very sensitive to changes in ionic strength.
  • As compared to the manual titration it needs an instrument that has two electrodes, an indicator, and a reference electrode.


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Thursday, July 29, 2021

Principle and types of potentiometric titration

Learn about the principle, types, and applications of potentiometric titration, that measures the potential between two electrodes as a function of the added reagent volume.

Titration is a commonly used analytical technique in laboratories for estimating the concentration of an analyte in a sample solution since it has various advantages and applications. 

Titration is also known as volumetric or titrimetry analysis since volume measurement is significant in titration.


What is potentiometric titration?

Potentiometric titration is a type of volumetric method used to determine the amount of an analyte by adding measured increments of titrant until the end-point is completed. 

Following the titration, the potential difference between the indicator electrode and the reference electrode is determined under conditions where the thermodynamic equilibrium is maintained and the current passing through the electrodes does not disturb it. 

It involves determining and recording the cell potential (millivolts or pH) after each titrant addition. To perform the potentiometric titration indicator electrode (metal ion indicator and glass electrode) and a reference electrode are used. The calomel electrodes, hydrogen electrodes, and silver chloride electrodes are commonly used as reference electrodes. 

With the interested ions in the sample solution, the indicator electrode forms an electrochemical half cell and the other half cell forms by the reference electrode. The different apparatus used in the potentiometric titration are burette, pipette, conical flask, funnel, beaker, volumetric flask, wash bottle and stand, etc.

Principle of potentiometric titration:

The principle behind the potentiometry is that when a pair of electrodes is placed in a solution, the addition of a titrant or a change in the concentration of ions indicates the potential difference. The reference electrode has its potential value and when it is dipped into sample solution it is stable. 

The salt bridge is employed to keep the analyte solution from interfering with the reference solution. The solution whose potential is to be determined is referred to as an analyte solution. The indicator electrode is the one that reacts to changes in the analyte solution's potential.

The total electric potential is calculated as Ecell = Eind - Eref + Esol.
A chemical indicator is not used in this reaction; the electric potential across the material is instead measured.

Types of potentiometric titration:

Potentiometric titration is a laboratory method used in the characterization of acids similar to direct titration of a redox reaction. Potentiometric titration can perform the following 4 types of titrations.

Acid-base titration:

An acid-base titration is a quantitative analysis used to determine the acid or base concentration by precisely neutralizing the acid or base with a known concentration standard solution. 

Titration of HCl with NaOH is an example in which a pH indicator (Generally phenolphthalein) is used to produce color by which the equivalence point or endpoint of the reaction determines. It is also can be performed by potentiometric titration however it doesn’t need an indicator. 

Redox titration:

It is a type of titration it includes the use of a redox indicator or potentiometer. It works based on an oxidation-reduction reaction between the titrant and the compound. Iodometry, permanganometry, bromatometry, cerimetry, and dichrometry are some of the most used redox titrations. A platinum or calomel electrode is also used in redox titration using a potentiometer.

Complexometric titration:

In this type of potentiometric titration, membrane electrodes are used to determine the concentration of metal ions in the compound sample. In the reaction of this method, a metal indicator complex is formed when the metal ion reacts with the indicator. 

Complexometric titration consists of replacement titration, back titration, direct titration, and indirect titration.

Precipitation titration:

It is a titration method that involves the formation of precipitates throughout the process of titration. The titrant reacts with the solute to form an insoluble substance, and the titration is carried until the last drop of the solute has been consumed. 

Depending on the type of application it consists of Volhard’s method, Mohr's method, and Fagan’s method.

Applications of potentiometric titration:

  • Potentiometric titration is used in environmental analysis.
  • It is used in different industries such as pharmaceutical, food, and detergent, etc.
  • To detect different elements in soils, fertilizers, etc. it is used in the agriculture sector.
  • It is used to determine the equivalence point of an acid-base solution.
  • It is broadly used for the assay of several official compounds.
  • It is used in clinical chemistry for the analysis of metals
  • It is used in environmental chemistry for the analysis of water and wastewater.  


Commonly asked questions on potentiometric titration are as follows.

What is the importance of potentiometric titration?
Potentiometry is important for determining a sample solution's electromotive force or potential. The ion concentration is directly proportional to the potential.

What is the electrode used in potentiometric titrations?
In a potentiometric titration, calomel and silver/silver chloride electrodes are most commonly used. A mercurous sulfate electrode can be used in halide determination.

Why are indicators used in titration?
The indicators are used in titration for the detection of endpoints of reactions. The color of an indicator changes when the acidity or oxidizing power of a solution reaches a critical range of values.
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