Chemistry Lecture 4: Titration PDF

Chemistry Lecture 4: Areej A. M. Osman MSc. Pharm. Chem. U of K 2020 BSc. Pharmacy U of K 2014 Learning outcomes By the end of this lecture the student should be able to: Define titration Describe the titration process Determine the types of titrations Define indicators Discuss end point...

Chemistry Lecture 4: Areej A. M. Osman MSc. Pharm. Chem. U of K 2020 BSc. Pharmacy U of K 2014 Learning outcomes By the end of this lecture the student should be able to: Define titration Describe the titration process Determine the types of titrations Define indicators Discuss end point detection Calculate concentration of unknown samples 10/14/2024 Areej A. M. Osman 2 Chemical Analysis (A)Classical: 1- Qualitative methods: Identification by color, indicators, boiling points, odors. 2- Quantitative methods: Measurment of mass or volume (e.g. gravimetric, volumetric) 10/14/2024 Areej A. M. Osman 2 Chemical Analysis (B)Non-classical or Instrumental 1- Qualitative instrumental analysis: It is the measurement of a property indicates presence of analyte. 2- Quantitative instrumental analysis: It is that magnitude of measured property is proportional to concentration of analyte. 10/14/2024 Areej A. M. Osman 2 Volumetric methods (Titration): It determins the volume of a solution of accurately known concentration which is required to react quantitatively with a measured volume of a solution of the substance to be determined. It has four different types according to the chemical reaction that occurs. Acid-base titrations Precipitation titrations Oxidation reduction titrations Complexometric titrations 10/14/2024 Areej A. M. Osman 2 Volumetric methods (Titration): The solution of accurately known concentration is called standard solution or the titrant. The substance being titrated is termed the titrand or the analyte. The standard solution is usually added from a long graduated tube called burette, to react with the analyte. The end of the reaction is determined by a substance the makes a visual change known as the indicator. The volume of the titrant is then used to determine the concentration of the analyte. 10/14/2024 Areej A. M. Osman 2 Equivalence point and end point The equivalence point of a titration is a theoretical point that can not be determined experimentally. Instead, we can only estimate its position by observing some physical change associated with the condition of equivalence. This change is called the end point for titration. 10/14/2024 Areej A. M. Osman 2 General titration process Prepare the standard solution (titrant) and wash the burette with distilled water the with standard solution. Prepare the sample solution (titrand, analyte) and transfer it into a clean conical flask (Erlenmeyer flask). Add the indicator to the analyte solution. Start the titration by adding standard solution from the burette until the color (generally) of the sample solution changes. Record the volume of standard solution and calculate the concentration of the analyte. 10/14/2024 Areej A. M. Osman 2 Titration Criteria To use titrations in analysis, the following conditions are essential: 1- There must be a simple complete reaction between standard solution and analyte, expressed by a chemical equation. 2- The reaction should be relatively fast. 3- Detectable, There must be an alteration in some physical or chemical property of the solution at the equivalence point. 4- An indicator should be used to define the end point of the reaction by a change in physical properties (eg color). 10/14/2024 Areej A. M. Osman 2 Standard solution Standard solution is the reagent of exactly known concentration that is used in titrimetric analysis. Standard solutions play a central role in all titrimetric method of analysis. Therefore we need to consider the desirable properties for such solutions, how they are prepared and how their concentration are expressed. 10/14/2024 Areej A. M. Osman 2 Properties of standard solution 1- Sufficiently stable so that it is only necessary to determine the concentration once. 2- React rapidly with the analyte so that the time required between additions of reagent is minimized. 3- React more or less completely with the analyte so that satisfactory end points are realized. 4- Undergo a selective reaction with the analyte that can be described by simple balanced equation. Indicators An indicator is a substance that is capable to make a visual change when the sample is completely consumed. Different types of titrations need different types of indicators. The visual change the happens is a result of structural change in the indicator. The moment this visual change happens is the end point of the titration. Indicators Examples of indicators: Indicators Examples of indicators: Indicators Examples of indicators: Titration Process Wash the burette with tab water, distilled water and the titrant. Fill the burette with the titrant and adjust the volume. Weigh the analyte and transfer it into the conical flask. Add a suitable amount of solvent to dissolve the analyte. Add 2-3 drops of the indicator. Start the titration until the color changes Record the volume and calculate the analyte’s concentration Titration Calculations In the titration, number of moles react with each other. NaOH + HCl → NaCl + H2O Molar ratio: 1 mole NaOH = 1 mole HCl no. of moles = M x V (mL) / 1000 = no of moles = wt /Mwt = Titration Calculations 10 mL of NaOH solution was titrated with HCl standard solution (0.2M) the volume of HCl cosumed was found 15 mL, what is the molarity of NaOH? NaOH + HCl → NaCl + H2O 1 mole : 1 mole = = ,M= = 0.3 M Titration Calculations 25 mL of NaOH solution was titrated with H2SO4 standard solution (0.1M) the volume of the acid cosumed was found 20 mL, what is the molarity of NaOH? 2 NaOH + H2SO4 → Na2SO4 + H2O 2 mole : 1 mole = = ,M= = 0.08 M  Any question? 10/14/2024 Areej A. M. Osman 2