PDF Download: Advances and Challenges in Complexometric Titrations
Application of Complexometric Titration PDF Download
Complexometric titration is a type of volumetric analysis that involves the formation of a complex between a metal ion and a ligand. A ligand is a molecule or ion that can donate one or more pairs of electrons to form a coordinate bond with a metal ion. A complex is a stable entity that results from the combination of a metal ion and one or more ligands.
application of complexometric titration pdf download
Complexometric titrations are widely used for the quantitative determination of various metal ions in different samples, such as water, soil, food, pharmaceuticals, etc. The most common ligand used in complexometric titrations is ethylenediaminetetraacetic acid (EDTA), which is a hexadentate ligand that can form very stable complexes with most metal ions.
Principles of Complexometric Titrations
The principle of complexometric titration is based on the equilibrium between the metal ion and the ligand. The reaction can be represented as follows:
M + Lm MLm
where M is the metal ion, L is the ligand, m is the number of ligands attached to the metal ion, n is the charge of the metal ion, and p is the charge of the ligand.
The equilibrium constant for this reaction is given by:
Kf = [MLm] / ([M] [Lm])
where Kf is the formation constant or stability constant of the complex, and [ ] denotes the concentration.
The formation constant indicates how stable the complex is. The higher the value of Kf, the more stable the complex and the more complete the reaction. The formation constant depends on several factors, such as the nature of the metal ion and the ligand, the pH of the solution, the temperature, etc.
In a complexometric titration, a known volume of a standard solution of a ligand (usually EDTA) is added gradually to a solution containing an unknown amount of a metal ion. The end point of the titration is detected by using an indicator that changes color when all the metal ions have reacted with the ligand. The indicator is usually another ligand that forms a less stable complex with the metal ion than EDTA. The indicator changes color when it is released from the metal ion by EDTA.
Methods and Applications of Complexometric Titrations
There are different methods and applications of complexometric titrations depending on the type of metal ion, ligand, indicator, pH, etc. Some of the common methods are:
Direct titration: This is the simplest method where EDTA is added directly to the metal ion solution until the end point is reached.
Back titration: This method is used when the metal ion forms a very stable complex with EDTA or when it precipitates in alkaline solution. In this case, an excess amount of EDTA is added to the metal ion solution and then the excess EDTA is titrated back with a standard solution of another metal ion (such as Mg or Zn) until the end point is reached.
Displacement titration: This method is used when the metal ion forms an insoluble compound with another reagent (such as oxalate or sulfide) or when it interferes with other metal ions in solution. In this case, a known amount of another metal ion (such as Pb or Cd) that forms a more stable complex with EDTA than the analyte metal ion is added to displace it from its compound or complex. Then, EDTA is added to titrate the displaced metal ion until the end point is reached.
Metallochromic indicator titration: This method is used when there is no suitable indicator that changes color at the end point. In this case, a metallochromic indicator (such as Eriochrome Black T or Calmagite) that forms a colored complex with both EDTA and
the analyte metal ion is used. The indicator changes color when it shifts from one complex to another as EDTA is added.
Some of the common applications of complexometric titrations are:
Determination of hardness of water by titrating calcium and magnesium ions with EDTA using Eriochrome Black T as an indicator.
Determination of zinc in ores by back titrating excess EDTA with standard zinc solution using xylenol orange as an indicator.
Determination of lead in paints by displacement titrating lead oxalate with EDTA using murexide as an indicator.
Determination of copper in alloys by direct titrating copper(II) ions with EDTA using Calmagite as an indicator.
PDF Download: Application of Complexometric Titration
If you are interested in learning more about complexometric titrations and their applications, you can download this PDF file that contains detailed information and examples on this topic. You will also find useful tips and tricks on how to perform accurate and precise complexometric titrations in different situations.
To download this PDF file, click on this link: Application of Complexometric Titration PDF Download
Advantages and Disadvantages of Complexometric Titrations
Complexometric titrations have several advantages over other types of titrations, such as:
They are simple, rapid, and accurate.
They can be used for a wide range of metal ions with different oxidation states and coordination numbers.
They can be performed in various media, such as aqueous, non-aqueous, or mixed solvents.
They can be easily automated and coupled with other analytical techniques, such as spectrophotometry or potentiometry.
However, complexometric titrations also have some limitations and drawbacks, such as:
They require a suitable indicator that can detect the end point with a sharp color change.
They may suffer from interferences from other metal ions or ligands that can form complexes with the titrant or the analyte.
They may be affected by the pH of the solution, which can influence the stability and solubility of the complexes.
They may require masking or demasking agents to prevent or promote the complexation of certain metal ions.
Tips and Tricks for Complexometric Titrations
To perform successful complexometric titrations, some tips and tricks are:
Choose an appropriate ligand and indicator for the metal ion to be determined.
Adjust the pH of the solution to ensure the complete complexation of the metal ion and the indicator.
Add a buffer solution to maintain a constant pH during the titration.
Add masking or demasking agents if necessary to eliminate or enhance the complexation of interfering metal ions.
Use a burette with a glass stopcock to avoid contamination of EDTA by metal ions from rubber or plastic parts.
Standardize the EDTA solution frequently using a primary standard or a certified reference material.
Avoid exposure of EDTA solution to air, light, or heat, which can cause decomposition or oxidation.
Avoid precipitation or hydrolysis of metal ions or complexes by using appropriate solvents and concentrations.
Examples of Complexometric Titrations
To illustrate the application of complexometric titrations, here are some examples of how to perform and calculate complexometric titrations using EDTA as the titrant.
Example 1: Determination of Hardness of Water
Hardness of water is a measure of the concentration of calcium and magnesium ions in water. Hard water can cause scaling and corrosion problems in pipes and boilers, as well as reduce the effectiveness of detergents and soap. One way to determine the hardness of water is by titrating a sample of water with EDTA using Eriochrome Black T as an indicator.
Eriochrome Black T is a metallochromic indicator that forms a wine-red complex with Ca and Mg ions in water. When EDTA is added, it displaces the indicator from the metal ions and forms a more stable complex. The indicator then changes color from wine-red to blue, indicating the end point of the titration.
The procedure for this titration is as follows:
Pipette 25.00 mL of water sample into a 250 mL conical flask.
Add 2 mL of ammonia-ammonium chloride buffer solution (pH 10) to adjust the pH.
Add a few drops of Eriochrome Black T indicator to the flask.
Titrate the solution with 0.01 M EDTA solution until the color changes from wine-red to blue.
Record the volume of EDTA used as VEDTA.
The calculation for this titration is as follows:
The balanced equation for the reaction between EDTA and Ca or Mg is:
Ca + H4Y CaY + 2H
Mg + H4Y MgY + 2H
The molarity of EDTA solution is given by:
MEDTA = 0.01 M
The moles of EDTA used are given by:
nEDTA = MEDTAVEDTA
The moles of Ca or Mg in the water sample are equal to the moles of EDTA used, since the reaction has a 1:1 stoichiometry.
nCa+nMg= nEDTA
The concentration of Ca or Mg in the water sample is given by:
CCa+CMg= nCa+nMg/Vwater
The hardness of water is usually expressed in terms of mg/L or ppm of CaCO3, which is equivalent to 1 mmol/L or meq/L. To convert the concentration of Ca+Mg(in mol/L) to hardness (in mg/L or ppm), we need to multiply by the molar mass of CaCO3(100.09 g/mol) and divide by 1000 (to convert g/L to mg/L).
H = (CCa+CMg) 1000 100.09 / 1000 = (CCa+CMg) 100.09 mg/L or ppm CaCO3
Example 2: Determination of Zinc in Ores
Zinc is an important metal that is used in various industries, such as galvanizing, alloys, batteries, etc. One way to determine the amount of zinc in ores is by back titrating excess EDTA with standard zinc solution using xylenol orange as an indicator.
Xylenol orange is a metallochromic indicator that forms a red complex with Zn(II) ions in acidic solution. When EDTA is added, it displaces the indicator from Zn(II) ions and forms a more stable complex. The indicator then changes color from red to yellow, indicating the end point of the titration.
The procedure for this titration is as follows:
Weigh about 0.5 g of ore sample and transfer it into a 250 mL conical flask.
Add about 20 mL of distilled water and 10 mL of concentrated hydrochloric acid to dissolve the ore sample.
Add about 10 mL of concentrated nitric acid and heat gently until all nitrous fumes are expelled.
Cool the solution and dilute it to about 100 mL with distilled water.
Add an excess amount (about 25 mL) of 0.01 M EDTA solution to the flask and mix well.
Add a few drops of xylenol orange indicator to the flask.
Titrate the excess EDTA with 0.01 M Zn(II) solution until the color changes from yellow to red.
Record the volume of Zn(II) solution used as VZn(II).
The calculation for this titration is as follows:
The balanced equation for the reaction between EDTA and Zn(II) is:
Zn(II) + H4Y^2- -> ZnY^2- + 2H+
The molarity of EDTA and Zn(II) solutions are given by:
MEDTA = MZn(II) = 0.01 M
The moles of EDTA added are given by:
nEDTA = MEDTA * VEDTA
The moles of Zn(II) used are given by:
nZn(II) = MZn(II) * VZn(II)
The moles of Zn(II) in excess are equal to the moles of Zn(II) used minus the moles
of EDTA added, since the reaction has a 1:1 stoichiometry.
nZn(II)_excess = nZn(II) - nEDTA
The moles of Zn(II) in the ore sample are equal to the moles
of EDTA added minus the moles
of Zn(II) in excess.
nZn(II)_ore = nEDTA - nZn(II)_excess
The mass percentage of Zn(II) in the ore sample is given by:
%Zn(II)_ore = (nZn(II)_ore * MZn / m_ore) * 100%
where MZn is the molar mass
of Zn (65.38 g/mol) and m_ore
is
the mass
of ore sample (in g).
Conclusion
Complexometric titrations are a powerful and versatile method for the quantitative analysis of metal ions in various samples. By using a suitable ligand, such as EDTA, and an appropriate indicator, such as Eriochrome Black T or xylenol orange, complexometric titrations can provide accurate and precise results for a wide range of metal ions with different properties and applications. Complexometric titrations can also be performed in different ways, such as direct, back, displacement, or metallochromic indicator titrations, depending on the specific requirements and conditions of the analysis. Complexometric titrations have many advantages over other types of titrations, such as simplicity, speed, accuracy, versatility, and automation. However, complexometric titrations also have some limitations and drawbacks, such as interferences, pH dependence, masking or demasking agents, and reagent stability. Therefore, complexometric titrations require careful selection and preparation of the reagents, indicators, buffers, and solvents, as well as proper standardization and calibration of the solutions and instruments.
If you want to learn more about complexometric titrations and their applications, you can download this PDF file that contains detailed information and examples on this topic. You will also find useful tips and tricks on how to perform accurate and precise complexometric titrations in different situations.
To download this PDF file, click on this link: Application of Complexometric Titration PDF Download 4e3182286b