chem lec.pdf

Volumetric analysis and principles of titration  Chemical analysis Quantitative Descriptive analysis analysis Volumetric Mass analysis analysis ⚫ Titratio...

Volumetric analysis and principles of titration  Chemical analysis Quantitative Descriptive analysis analysis Volumetric Mass analysis analysis ⚫ Titration is the slow addition of one solution of a known concentration (called a titrant) to a known volume of another solution of unknown concentration until the reaction reaches neutralization, which is often indicated by a colorchange.  Key Concepts: Titration (Volumetric analysis) Volumetric analysis: ▪ Is refers to as titrimetric analysis. ▪ It refers to a quantitative chemical analysis of a solution using accurate volumes. Volumetric analysis requires: ▪ Extremely clean glassware ▪ Great care in taking and recording measurements To be used in volumetric analysis, a reaction must: ▪ Selective: The chemical reaction between the analyte and the titrant must be selective (only the analyte should react with the titrant). ▪ Fast: The reaction should be fast in order to guarantee that the added titrant reacts immediately with the analyte. ▪ Complete: The equilibrium of the reaction should lie strongly on the product side of the reaction to guarantee a complete reaction. ▪ Unambiguous: The stoichiometry of the reaction must be known and unambiguous. Key Concepts: Volumetric glassware to be used: Volumetric flask: used to prepare and store a standard solution of known concentration. Pipette: used to deliver an accurate volume (aliquot) of solution. Burette: used to deliver and measure the volume of a solution. Aliquot: an accurately known volume of solution (delivered by pipette). Titrant: solution of known concentration. Titrate: solution being titrated in order to determine its concentration. Titre: total volume of solution delivered by the burette to reach the end point of the titration. ▪ Titration is the determination of the quantity of a specific substance (analyte) contained in a sample by controlled addition of a reagent (titrant) of known concentration based on a complete chemical reaction between the substance and the reagent. ▪ Example: Determination of acetic acid (CH3COOH) by titration with sodium hydroxide (NaOH) CH3COOH + NaOH CH3COONa + H2 O (analyte) (titrant) (reaction products) ▪ Practical Procedure: - The sample (e.g. vinegar) is diluted pH value (= sample solution with low acidic). - A NaOH solution of known concentration (titrant) is carefully added to the acidic solution (titration). - The analyte (CH3COOH) reacts with the titrant (NaOH) ( pH rises slowly from acidic to basic). - As soon as all analyte has reacted, the pH rises immediately (excess of NaOH in the solution) equivalence point. ▪ Content calculation: Sample size is known. Concentration of titrant is known. Titrant consumption (volume) until the equivalence point is measured during titration. The acetic acid content in the sample can be calculated from these three variables. 9 ▪ Apparatus: The standard equipment includes the following : Burette: for accurate titrant addition Titration beaker or conical flask Stirrer Burette ▪ Several prerequisites have to be fulfilled in order to perform a successful titration: Suitable reaction needed (reaction between the titrant and the analyte) Titrant concentration and used volume must be known very accurately Equivalence point must be detectable Conical flask stirrer 1 0 the volume of titrant used until the equivalence point. ▪ The key point of a good titration is the accurate determination of ▪ The equivalence point is the point in a titration where the amount of titrant added is enough to completely neutralize the analyte solution. The moles of titrant (standard solution) equal the moles of the solution with unknown concentration. ▪ Endpoint refers to the point at which the indicator changes colour in an acid-base titration. ▪ For this reason the following two requirements have to be fulfilled: - A titrant addition in small quantities must be possible. - An accurate reading for the volume used is needed. ▪ A manual burette fulfills these requirements: - Stopcock: add small volumes - Grading: accurate volume reading Applications of titration ▪ Chemical industry: Water content in solvents, acid value in resins and polymers, hydroxyl value in polyols, surfactant content in raw materials, … ▪ Food and beverage: Acid and vitamin C content in fruit juices, chloride content in spicy sauces, nitrite content in food products, … ▪ Electroplating: Nickel content in electroless bath, gold and silver content in alloys, chromium content in electroplating baths, …zz 3  Applications of titration ▪ Pharmaceutical: Water contents in raw products, chondroitin sulfate sodium in tablets, purity and content of different active pharmaceutical ingredients like benzylnicotinate, clotrimazol and diclofenac sodium, … ▪ Petrochemical: Acid and base number in oils, mercaptane sulfur content in kerosene, chloride content in motor oil. ▪ Environmental: Total hardness of water, copper content in aqueous solution, residual chlorine in bleach, fluoride content in water, … 4  Types of Titration There are many types of titration when considering goals and procedures. However, the most common types of titration in quantitative chemical analysis are redox titration and acid- base titration. Titrations can be classified as: A. Acid-base Titrations B. Precipitation Titrations. C. Redox Titrations. D. Complexometric Titrations.