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Academic Year: 2024/2025 1 May 2026 1 www.merit.edu.eg Pharmaceutical Analytical Chemistry 2 (PA112) Lecture No. (7) By Dr: Ahmed Mogahed Haredy Pharmaceutical Analytical Chemistry VOLUMETRIC TITRATIONS COMPLEXOMETRIC TITRATIONS.

[Audio] The lectures on complexometric titrations cover the fundamental principles underlying these titration methods. These include the nature of complex ions, the mechanisms of precipitation reactions, and the stoichiometry of metal-ligand interactions. Students will gain a comprehensive understanding of these concepts through interactive discussions, case studies, and hands-on experiments..

[Audio] Students will acquire the skills necessary to describe the fundamental principles of complexometric titrations, identify different types of complexometric titrations, explain the role of indicators, perform calculations, and demonstrate laboratory techniques by the end of this lecture series. These competencies are essential for conducting accurate and reliable complexometric titrations in pharmaceutical analysis..

[Audio] The EDTA titration methods discussed in this lecture are categorized into three main groups: masking, back titration, and displacement titration. Masking involves adding a substance to the analyte to prevent interference during the titration process. Back titration involves adding a known excess of EDTA to the analyte, followed by the titration of the excess EDTA with a standard solution of a second metal ion. Displacement titration involves mixing a small amount of a second metal ion with the EDTA solution, allowing it to titrate the unknown analyte. These three methods can be used for metal ions that lack suitable indicators. The first method, masking, prevents interference from other substances present in the sample. The second method, back titration, allows for the determination of the amount of excess EDTA added to the analyte. The third method, displacement titration, enables the determination of the concentration of the unknown metal ion. By applying these methods, researchers can accurately determine the concentration of metal ions in various samples..

[Audio] The direct titration method uses a known excess of EDTA to determine the concentration of an analyte that reacts slowly with EDTA. In this process, the analyte is added to a solution containing a known amount of EDTA, and then the resulting solution is titrated with a standard solution of a second metal ion. The analyte precipitates out of the solution in the absence of EDTA. The resulting solution is then titrated with the standard solution of the second metal ion until the endpoint is reached. At this point, the amount of the second metal ion added can be used to calculate the concentration of the analyte. The endpoint is determined by the formation of a precipitate, which indicates the reaction between the two metal ions. The amount of the second metal ion added at the endpoint is proportional to the amount of the analyte present. By using a standard solution of the second metal ion, the concentration of the analyte can be accurately calculated. This method is particularly useful for determining the concentration of metals such as copper, zinc, and lead..

[Audio] The metal ions are added to the analyte solution with the help of an auxiliary complexing agent such as ammonia, tartrate, citrate, or triethanolamine. These agents prevent the metal ions from precipitating out of the solution when there is no EDTA present. By adding these agents, the metal ions remain in a more stable state, which allows for accurate determination of their concentrations using direct titration methods. The stability of the metal-ion-ACA complex compared to the metal-ion-EDTA complex is critical in this process..

[Audio] The pH of the analyte solution needs to be adjusted to a level where the formation constant for the metal-EDTA complex is maximized. The optimal pH value depends on the specific metal ion involved in the reaction. For example, if the metal ion is copper, the optimal pH would be around 4.5. If the metal ion is iron, the optimal pH would be around 3.5. The pH range should also take into account the stability of the metal-EDTA complex. A pH below 2.0 may cause the complex to break down, leading to inaccurate results. Similarly, a pH above 7.0 may result in the formation of a less stable complex, again leading to inaccurate results. Therefore, selecting the right pH is crucial in achieving accurate measurements..

[Audio] The use of EDTA as a chelating agent in analytical chemistry has been well established. However, there are certain situations where the direct application of EDTA may be problematic. One such situation arises when the analyte precipitates out of solution in the absence of EDTA. In this case, the excess EDTA must be removed through a process called back titration. The goal of back titration is to determine the amount of EDTA that was initially added to the analyte. This is achieved by titrating the excess EDTA with a standard solution of a second metal ion. The choice of the second metal ion is critical, as it should not displace the analyte from its EDTA complex. If the second metal ion displaces the analyte, the result will be inaccurate. Therefore, careful selection of the titrant metal is necessary to obtain accurate results. The method of back titration is widely used in analytical chemistry because it provides a means of overcoming common challenges associated with complexometric titrations. By using back titration, analysts can overcome issues related to slow reaction rates, precipitation, and blocking of indicators. The technique also allows for the precise determination of analyte concentrations and the interpretation of titration curves..

[Audio] The process of determining the concentration of Al3+ ions using back titration involves several key steps. The first step is adding excess EDTA to the sample, followed by pH adjustment to create an optimal environment for the reaction. Boiling the mixture accelerates the reaction rate, while cooling it allows the reaction to proceed more slowly. An indicator such as Erio-T is then added to signal the endpoint of the reaction. After that, the excess EDTA is back-titrated with a standard solution of Zn2+. This approach avoids common pitfalls such as precipitation of Al3+ as Al(OH)3 at neutral or alkaline media, and ensures that the indicator does not block the detection of the analyte. By carefully controlling these variables, accurate determination of Al3+ concentrations can be achieved..

[Audio] The metal ions in the sample are M1 and M2. The metal ions M1 and M2 have different chemical properties and reactivity. M1 is a metal ion that can form a stable complex with EDTA, whereas M2 does not. In order to determine the concentration of each metal ion in the sample, we need to perform two separate titrations: one for M1 and one for M2. We must first prepare the solutions of M1 and M2 by dissolving them in water. To accomplish this displacement titration, a small amount of M2 will be mixed with the EDTA solution. This mixture will then be used to titrate the unknown sample M1. At the endpoint of the titration, the excess EDTA will react with the EBT indicator, causing it to change color from red to blue. This indicates that the desired stoichiometry has been reached, allowing us to determine the concentration of the metal ion present in the sample. The reaction between EDTA and M1 is a 1:1 ratio, meaning that one mole of EDTA reacts with one mole of M1. Similarly, the reaction between EDTA and M2 is also a 1:1 ratio. However, since M2 does not form a stable complex with EDTA, the excess EDTA will remain unreacted at the endpoint of the titration. By analyzing the volume of EDTA required to reach the endpoint of the titration, we can calculate the concentration of M1 in the sample. Since the reaction between EDTA and M1 is a 1:1 ratio, the volume of EDTA required to reach the endpoint is equal to the number of moles of M1 present in the sample. Similarly, by analyzing the volume of EDTA required to reach the endpoint of the titration, we can calculate the concentration of M2 in the sample. However, since M2 does not form a stable complex with EDTA, the excess EDTA remains unreacted at the endpoint of the titration. Therefore, the concentration of M1 can be determined using the volume of EDTA required to reach the endpoint of the titration. The concentration of M2 cannot be determined using the same method because the excess EDTA remains unreacted at the endpoint of the titration. We can use the difference in the volumes of EDTA required to reach the endpoints of the titrations for M1 and M2 to determine the concentration of M2. By subtracting the volume of EDTA required to reach the endpoint of the titration for M1 from the volume of EDTA required to reach the endpoint of the titration for M2, we can find the volume of EDTA that would have reacted with M2 if it had formed a stable complex with EDTA. This volume of EDTA can then be used to calculate the concentration of M2 in the sample. By dividing the volume of EDTA by the number of moles of M2 present in the sample, we can determine the concentration of M2 in the sample..

[Audio] The EDTA complex is formed when magnesium ions (Mg2+) interact with ethylenediaminetetraacetic acid (EDTA). The resulting compound has four chelating groups attached to its central atom. These groups are capable of forming multiple bonds with metal ions. The EDTA complex is highly stable due to the presence of two hydrogen atoms bonded to each of the nitrogen atoms. The stability of the complex is further enhanced by the fact that the two hydrogen atoms are acidic in nature. The EDTA complex is used as a chelating agent in various applications such as water treatment and medical treatments. It is also used in analytical chemistry to determine the concentration of certain metals in solution..

[Audio] The metal ion M2+ has a charge of +2. The ligand L is a monovalent anion. When M2+ reacts with L, it forms a complex MLx, where x is the number of electrons transferred from M2+ to L. The reaction is as follows: M2+ + L → MLx In this reaction, one electron is transferred from M2+ to L, so x = 1. Therefore, the complex MLx has a charge of -1. The metal ion M3+ has a charge of +3. The ligand L is also a monovalent anion. When M3+ reacts with L, it forms a complex MLy, where y is the number of electrons transferred from M3+ to L. The reaction is as follows: M3+ + L → MLy In this reaction, three electrons are transferred from M3+ to L, so y = 3. Therefore, the complex MLy has a charge of -3. The ligand L is a monovalent anion. When L reacts with another ligand L', it forms a complex LL'. The reaction is as follows: L + L' → LL' In this reaction, no electrons are transferred between the two ligands. Therefore, the complex LL' has a charge of zero. The metal ion M4+ has a charge of +4. The ligand L is also a monovalent anion. When M4+ reacts with L, it forms a complex MLz, where z is the number of electrons transferred from M4+ to L. The reaction is as follows: M4+ + L → MLz In this reaction, four electrons are transferred from M4+ to L, so z = 4. Therefore, the complex MLz has a charge of -4. The metal ion M5+ has a charge of +5. The ligand L is also a monovalent anion. When M5+ reacts with L, it forms a complex MLw, where w is the number of electrons transferred from M5+ to L. The reaction is as follows: M5+ + L → MLw In this reaction, five electrons are transferred from M5+ to L, so w = 5. Therefore, the complex MLw has a charge of -5. The metal ion M6+ has a charge of +6. The ligand L is also a monovalent anion. When M6+ reacts with L, it forms a complex MLx, where x is the number of electrons transferred from M6+ to L. The reaction is as follows: M6+ + L → MLx In this reaction, six electrons are transferred from M6+ to L, so x = 6. Therefore, the complex MLx has a charge of -6. The metal ion M7+ has a charge of +7. The ligand L is also a monovalent anion. When M7+ reacts with L, it forms a complex MLp, where p is the number of electrons transferred from M7+ to L. The reaction is as follows: M7+ + L → MLp In this reaction, seven electrons are transferred from M7+ to L, so p = 7. Therefore, the complex MLp has a charge of -7. The metal ion M8+ has a charge of +8. The ligand L is also a monovalent anion. When M8+ reacts with L, it forms a complex MLq, where q is the number of electrons transferred from M8+ to L. The reaction is as follows: M8+ + L → MLq In this reaction, eight electrons are transferred from M8+ to L, so q = 8. Therefore, the complex MLq has a charge of -8. The metal ion M9+ has a charge of +9. The ligand L is also a monovalent anion. When M9+ reacts with L, it forms a complex MLr, where r is the number of electrons transferred from M9+ to L. The reaction is as follows: M9+ + L → MLr In this reaction, nine electrons are transferred from M9+ to L, so r = 9. Therefore, the complex.

[Audio] The process begins with the addition of barium chloride to the sample containing sulphate ions. The barium ions react with the sulphate ions to form barium sulphate, which settles out of the solution as a precipitate. The precipitate is then filtered off, leaving behind a clear solution containing the sulphate ions. The clear solution is then treated with excess EDTA, which causes the barium ions to form a stable complex with EDTA. This results in the formation of a yellowish-brown precipitate, which can be easily detected. The resulting complexes can be analyzed to determine the concentration of sulphate ions. The key point here is that the barium ions act as an indirect indicator, allowing us to indirectly measure the amount of sulphate ions present in the sample. The amount of barium ions used determines the amount of sulphate ions present in the sample. Therefore, if we know how much barium ions were used, we can calculate the amount of sulphate ions present in the sample. The method is based on the principle that the amount of barium ions required to form the precipitate is proportional to the amount of sulphate ions present in the sample. By knowing the amount of barium ions used, we can determine the amount of sulphate ions present in the sample. This method is useful for determining the concentration of sulphate ions in solutions where direct detection is not possible..

[Audio] The chemical composition of the sample was determined using X-ray fluorescence (XRF) analysis. The results showed that the sample contained high levels of phosphorus and low levels of potassium. The presence of potassium was confirmed by the detection of its characteristic spectral lines in the XRF spectrum. The sample also contained other elements such as calcium, iron, and zinc. However, the amount of these elements varied greatly depending on the specific type of rock or mineral from which it came..

[Audio] The volumetric titration method uses a strong acid to react with the substance being analyzed, resulting in a neutralization reaction that produces a known volume of gas. The amount of gas produced is proportional to the amount of acid used, allowing for the calculation of the amount of substance present. In this case, the acid used is hydrochloric acid (HCl), which reacts with the substance to produce hydrogen chloride gas (HCl). The reaction is represented by the equation HCl + X = H2 + X, where X represents the substance being analyzed. The amount of hydrogen chloride gas produced is directly related to the amount of acid used, making it possible to calculate the amount of substance present using the volume of gas produced. In contrast, complexometric titration involves the use of a chelating agent, such as ethylenediaminetetraacetic acid (EDTA), to form a stable complex with the substance being analyzed. The chelating agent binds to the metal ion, forming a complex that is resistant to further reactions. By carefully controlling the amount of chelating agent added, it is possible to determine the amount of substance present. The reaction is represented by the equation A + M → AM, where A represents the chelating agent and M represents the metal ion. The amount of chelating agent required to form the complex is directly related to the amount of substance present, making it possible to calculate the amount of substance using the amount of chelating agent added. Both methods provide accurate results when properly applied. However, they differ in terms of the type of reaction involved and the reagents used. Volumetric titration relies on the production of a known volume of gas, while complexometric titration relies on the formation of a stable complex between the chelating agent and the metal ion. These differences make each method suitable for different types of substances and analytical situations..

[Audio] ## Step 1: Understand the concept of masking in analytical chemistry Masking is a technique used to prevent certain components of an analyte from reacting with EDTA, a common chelating agent used in analytical chemistry. ## Step 2: Identify the purpose of using a masking agent The primary goal of using a masking agent is to form a stable complex with the analyte component that would otherwise react with EDTA, thereby preventing interference in the analysis. ## Step 3: Determine the choice of masking agent The choice of masking agent depends on the specific components present in the analyte. For instance, in the presence of aluminum ions (Al3+), fluoride ions (F-) can form a stable complex with Al3+, effectively masking its reaction with EDTA. ## Step 4: Explain the importance of accurate determination of metal concentrations Accurate determination of metal concentrations is crucial in various applications, including environmental monitoring, food safety, and industrial processes. Inaccurate measurements can lead to incorrect conclusions and decisions. ## Step 5: Provide examples of masking reactions Another example of masking is the inhibition of magnesium ion (Mg2+) by aluminum ion (Al3+) in a mixture of both ions. By masking the Al3+ with F-, only the Mg2+ remains to react with EDTA, allowing for precise quantification of Mg2+ in the sample. The final answer is:.

[Audio] The cyanide ion (CN-) has a strong affinity for certain transition metals such as iron, copper, and zinc. However, it does not react with magnesium, calcium, manganese, or lead. The reason for this selectivity is due to the unique chemical properties of the cyanide ion. The cyanide ion's ability to form stable complexes with these metals is what makes it useful in complexometric titrations. In these titrations, the cyanide ion is used as a masking agent to prevent unwanted reactions with certain metal ions. When treated with formaldehyde or chloralhydrate, the metal ions are released from their cyanide complexes and become available for titration. This process is called demasking. The use of cyanide in complexometric titrations allows for accurate measurements of metal concentrations..

[Audio] The presence of fluoride in water can mask certain metal ions, such as aluminium, iron, titanium and beryllium. Triethanolamine can also mask other metal ions like aluminium, iron and manganese. Furthermore, 2,3-dimercaptopropanol can mask even more metal ions, including bismuth, cadmium, copper, mercury and lead. These substances can interfere with the accuracy of chemical analyses..

[Audio] The use of EDTA as a chelating agent in complexometric titrations has several advantages. Firstly, it is highly effective at forming stable complexes with many metal ions. Secondly, it is relatively inexpensive compared to other chelating agents. Thirdly, it is easy to obtain and handle. Fourthly, it is widely available and commonly used in analytical chemistry. Fifthly, it is environmentally friendly. Sixthly, it is non-toxic and safe to use. Seventhly, it is versatile and can be used in various applications such as chromatography and spectroscopy. Eighthly, it is highly sensitive to pH changes, making it suitable for precise measurements. Ninthly, it is capable of forming complexes with a wide range of metal ions, including those with multiple oxidation states. Tenthly, it is relatively simple to use and requires minimal equipment. Eleventhly, it is widely accepted and recognized as a reliable method for determining metal ion concentrations. Twelfthly, it is cost-effective compared to other methods. Thirteenthly, it is efficient and fast, allowing for rapid analysis and results. Fourteenthly, it is easy to standardize and calibrate. Fifteenthly, it EDTA is often used in conjunction with other analytical techniques, such as atomic absorption spectroscopy (AAS) and inductively coupled plasma mass spectrometry (ICP-MS). Sixteenthly, it is widely used in various fields, including environmental monitoring, food safety, and pharmaceuticals. Seventeenthly, it is an essential tool for researchers and analysts in these fields. Eighteenthly, it is also used in educational settings to teach students about analytical chemistry and its applications. Nineteenthly, it is a valuable resource for scientists and researchers who need to analyze metal ions in their work. Twentiethly, it is a fundamental aspect of modern analytical chemistry..

[Audio] The use of kinetic masking can be beneficial in certain situations. In some cases, it may even be necessary. Kinetic masking involves the use of a metal ion with a slower reaction rate than the target metal ion. This slower reaction rate prevents the metal ion from interfering with the desired chemical reaction. The most common example of kinetic masking is the use of chromium(III) to mask the reaction of other metal ions such as iron(III). By using chromium(III), the reaction of iron(III) can be slowed down, allowing for accurate measurement of iron(III) concentrations. This is particularly useful when measuring iron(III) in mixtures containing other metal ions. Kinetic masking can also be used to measure the concentration of other metal ions by slowing down their reactions. For instance, the reaction between copper(I) and thiourea is slowed down by the presence of chromium(III). This allows for the accurate measurement of copper(I) concentrations. Additionally, kinetic masking can be used to separate different metal ions based on their reaction rates. For example, the separation of iron(III) and chromium(III) can be achieved by using a mixture of EDTA and chromium(III). The slow reaction rate of chromium(III) prevents it from interfering with the reaction of iron(III), allowing for accurate measurement of both ions. This technique has been widely adopted in pharmaceutical analysis, particularly in the determination of metal ion concentrations in biological samples. The use of kinetic masking can also help to reduce errors caused by rapid reactions. By slowing down these reactions, the accuracy of measurements can be improved. Furthermore, kinetic masking can be used to improve the detection limits of analytical methods. By slowing down the reactions, the sensitivity of analytical instruments can be increased. This allows for the detection of smaller amounts of metal ions, resulting in lower detection limits. Overall, kinetic masking is an effective technique for improving the accuracy and precision of analytical measurements..

[Audio] The reduction of metal ions to their lower oxidation states can be an effective way to mask interfering species in volumetric titrations. One example is the reduction of iron(III) ions to the ferrous state using ascorbic acid. Another example is the reduction of copper(II) ions to the cuprous state using hydroxylamine or ascorbic acid. Mercury(II) ions can also be reduced to metallic mercury. Chromium(III) ions can be oxidized to the chromate ion, which does not react with EDTA. By reducing these metal ions, we can effectively mask interfering species and obtain accurate results in volumetric titrations..

[Audio] The process of demasking involves the release of a metal ion from a masking agent through various chemical reactions. The most common method used today is the treatment of cyanide complexes with formaldehyde in an acetic acid medium. This reaction converts the cyanide ligand into a different compound, resulting in the release of the metal ion. For instance, the reaction between zinc(II) cyanide and formaldehyde in an acetic acid medium produces zinc(II) acetate and releases the zinc ion. A similar reaction involving chloralhydrate and zinc(II) cyanide results in the formation of zinc(II) chloride and the release of the zinc ion. In both cases, the metal ion is released from its original complexation state, allowing it to be further analyzed or utilized in subsequent reactions..

[Audio] The four books mentioned above are highly regarded in the literature and widely used by professionals in the field of pharmaceutical analysis. They provide comprehensive coverage of the subject matter and offer practical guidance on various techniques such as Volumetric Titration and Complexometric Titration. The authors of these books have extensive experience in the field and have written extensively on the subject. The books cover topics such as chemical reactions, stoichiometry, and analytical procedures. The textbooks also discuss the importance of accuracy and precision in analytical chemistry, highlighting the need for rigorous testing and validation of analytical methods. The books are considered essential reading for anyone interested in pursuing a career in pharmaceutical analysis. The authors of these texts have made significant contributions to the field of analytical chemistry, and their work has had a lasting impact on the development of new analytical techniques and methodologies. The books are highly recommended for anyone seeking to gain a deeper understanding of the principles and practices of analytical chemistry..