Titration or titrate is derived from the French word titrer, which literally means chemical proportion. Thus, the dictionary definition of titration is to ascertain the quantity of a chemical constituent. In a chemist’s dictionary, however, the word titration sums up a diverse study of different experimental methods. In the chemistry laboratory, many different types of titrations are performed that serve multiple purposes. Conversely, different types of glassware, reagents, and indicators are used to make that possible.
So, in this special article in our titration series, we have tried to summarize the many different types of titrations and their working principle. This will help you revise all the concepts you have been learning with us through this series. Also, if you are new here, that too is absolutely fine because reading along the way, you will find everything you need to know about titration. So, let’s start reading!
What is titration-Definition
Titration is a volumetric analysis method. It is used to determine an analyte’s unknown concentration using a standard solution of known concentration.
The analyte solution is known as the titrand; it is usually taken in a conical titration flask. The standard solution is known as the titrant. It is dropwise added through a burette into the titration flask containing the titrand and an indicator. The endpoint of the titration is marked based on some physical and/or chemical change exhibited by the indicator.
What are the different types of titration
A titration experiment can be classified based on the:
- Chemical reaction taking place between titrant and analyte. For example, acid-base titration, redox titration, complexometric titration, etc.
- Indication method. A chemical reagent such as methyl orange can be used as an indicator in acid-base titration. Contrarily it can also be performed by measuring the change in potential difference; it would then fall under potentiometric titration.
- Titration principle. This includes direct titration versus indirect or back titration. In a direct titration method, the unknown analyte concentration is determined by titrating it with a single reagent of known concentration. However, in back titration, the unknown analyte concentration is determined by reacting it with an excess of reagent A. The unreacted amount of reagent A is, in turn, titrated with reagent B.
8 different types of titration
1. Acid-base titration
Acid-base titration is performed to determine the unknown concentration of an acid or a base by an acid-base neutralization reaction. The unknown acid is reacted with an equivalent amount of base (or vice versa). The indicator marks the endpoint of the titration by giving a color change at the pH at which its end-point coincides with the equivalence point for the acid-base chemical reaction.
Working principle and steps of an acid-base titration between HCl and NaOH
- A 0.1 M standard solution of HCl is prepared using distilled water in a volumetric glass flask.
- The HCl solution is filled into a burette. The initial burette reading (x1) is recorded by reading the lower meniscus.
- 10 mL NaOH solution is pipetted out in a titration flask.
- A few drops of an acid-base indicator, such as phenolphthalein, are added.
- The phenolphthalein indicator gives a light pink color at an alkaline pH.
- The HCl solution is added dropwise into the titration mixture until the indicator turns colorless with just one drop of HCl from the burette.
- The final burette reading (x2) is recorded.
- Difference between x2 and x1 gives the titre volume, i.e., the volume of 0.1 M HCl required to completely neutralize 10 mL NaOH.
- The titre volume, a balanced chemical equation for the reaction between HCl and NaOH, and the titration formula given below is then used to find the NaOH concentration initially present in the titration flask.
2. Redox titration
The redox titration is performed to determine the unknown concentration of an oxidizing or a reducing agent based on an oxidation-reduction or redox reaction. In a redox reaction, the reducing agent undergoes oxidation by losing electrons. Its oxidation state decreases. Contrarily, the oxidizing agent undergoes reduction by gaining the electrons lost by the reducing agent. The oxidizing agent gives a color change due to the change in its oxidation state. This marks the end point of the titration.
Working principle and steps of a redox titration between KMnO4 and FeSO4
- A 0.1 M solution of KMnO4 is prepared and filled in a burette.
- It is a deep purple colored solution. The color is due to Mn7+ ions.
- 10 mL FeSO4 is pipetted out in the titration flask. A small amount of an acid is also added.
- Dropwise addition of KMnO4 (oxidizing agent) into the titration flask containing FeSO4 (reducing agent) leads to reduction of Mn7+ to Mn2+ while oxidation of Fe2+ to Fe3+.
- As all the Fe2+ ions present in the titration mixture get oxidized to Fe3+, the excess of Mn7+ ions in the titration flask gives a dark pink or purple color to the mixture.
- This color persists for some time, marking the titration’s end point, and the titre volume is recorded.
3. Iodometric titration
The Iodometric titration is a sub-type of redox titration. It is based on the back titration principle. The unknown amount of an oxidizing agent is first reacted with an excess of iodide ions. The oxidation of the iodide (I–) ions (reducing agent) yields iodine (I2). The amount of iodine liberated is determined by titrating it with a standard sodium thiosulfate (Na2S2O3) solution. The initial analyte concentration is thus indirectly calculated by determining the amount of iodine liberated in the first reaction.
4. Iodimetric titration
Iodimetric titration is another sub-type of redox titration. However, unlike Iodometry, it is a direct titration method. The analyte, in this case, is a reducing agent. It is reacted with a known concentration of the iodine solution. The iodine solution acts as a mild oxidizing agent. Starch is used as an indicator in the Iodimetric titration.
In its solubilized form, Iodine exists as the triiodide (I3–) ions. The reduction of triiodide to iodine results in the formation of an iodine-starch complex that gives a blue-black color to the titration mixture. This marks the endpoint of the titration.
5. Complexometric titration
Complexometric titration is performed to determine the unknown concentration of metal ions using a ligand solution of known concentration. Organic dyes such as Eriochrome black T (EBT), Fast Sulphon Black, Calmagite, etc., are used as indicators in complexometric titration. The indicator itself is a ligand that can complex metal ions present in the sample solution. The indicator-metal complex possesses a different color from the color of the indicator in its free form.
The titration of the sample solution with a standard ligand solution result in the displacement of metal ions from the metal-indicator complex. This leads to a color change, marking the end point of the titration.
6. EDTA titration
The complexometric titration performed using ethylene diamine tetra acetic acid (EDTA) as a complexing agent, or ligand solution is referred to as EDTA titration.
Working principle and steps of EDTA titration for determining Ca2+ ions
- A 0.1 M standard solution of EDTA is prepared and filled into a 50 mL burette.
- 10 mL of Ca2+ sample is pipetted out into a titration flask.
- A few drops of EBT indicator are added.
- A small volume of a buffer solution is also added.
- EBT binds with Ca2+ ions present in the sample.
- The Ca2+-EBT complex gives a pink color to the sample solution.
- Dropwise addition of EDTA solution from the burette into the titration mixture displaces Ca2+ ions from the Ca2+-EBT complex.
- A Ca2+-EDTA complex is formed.
- As all the Ca2+ ions get displaced from the sample solution, and EBT is released in its free form, the solution changes color from pink to blue.
- The volume of EDTA used at this point helps determine the concentration of Ca2+ ions present in 10 mL of the sample solution.
7. Precipitation titration
In precipitation titration, the analyte reacts with a standard solution to form an insoluble solid called a precipitate. There are three different methods by which precipitation titration can be performed. These include Volhard’s method, Fajan’s method, and Mohr’s method of precipitation titration. Precipitation titration performed using a standard solution of silver nitrate (AgNO3) as the titrant is also called Argentometry.
Working principle and steps of Argentometric titration performed via Volhard’s method
- 10 mL of a sample solution containing Cl– ions is treated with an excess of AgNO3 solution.
- Cl– ions react with Ag+ ions to form AgCl precipitate.
- The white AgCl precipitate settles at the bottom of the reaction flask.
- Unreacted AgNO3 present in this mixture is then titrated with a standard solution of potassium thiocyanate (KSCN) using ferric ammonium sulfate (NH4Fe(SO4)) as the indicator.
- The indicator forms a red-colored complex and marks the end point of the titration.
- Once the amount of AgNO3 unreacted is determined, the amount of AgNO3 that reacted with Cl– ions in the first reaction and thus Cl– concentration can be conveniently determined.
8. Potentiometric titration
In a potentiometric titration, the electrical potential difference is measured between the indicator electrode and a reference electrode to determine the unknown analyte concentration. The indicator electrode is dipped into an electrolyte containing the analyte of interest. The reference electrode is usually a standard hydrogen electrode (SHE), an AgCl electrode, or a calomel (Hg2Cl2) electrode.
The two electrodes make the two half-cells of an electrochemical cell. Oxidation takes place at the anode, while reduction occurs at the cathode. An electromotive force (EMF) is generated as a result of this redox reaction. Change in EMF with respect to the volume of titrant added is plotted as the potentiometric titration curve.
All the images in this article are designed and created by Ammara W.
Lastly, practice some questions on titration.
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3. Kozak, Joanna, and Alan Townshend. 2019. ‘Titrimetry | Overview.’ in Paul Worsfold, Colin
4. Poole, Alan Townshend and Manuel Miró (eds.), Encyclopedia of Analytical Science (Third Edition) (Academic Press: Oxford).
5. Seely, Oliver. 2020. “Iodometric determination of Cu in Brass ” In.: LibreTexts Chemistry.