Acid-Base Titration PDF

Nineveh University College of Medicine Assistant Lecturer Asmaa H. Abbas Analytical Chemistry One of the branches of chemistry that is concerned with detecting elements and substances, methods of separating them, and knowing th...

Nineveh University College of Medicine Assistant Lecturer Asmaa H. Abbas Analytical Chemistry One of the branches of chemistry that is concerned with detecting elements and substances, methods of separating them, and knowing their components in a mixture. Classification of analytical chemistry? Analytical chemistry is classified into: 1- Qualitative analysis: means how to separate elements and substances Q from mixtures and identify them through separation. MC ‫يهتم‬ ‫تقدير‬ 2- Quantitative analysis: It is concerned with the quantitative estimation of the elements and compounds present in a sample. Quantitative Analysis ‫ا>لية‬ Classical methods Instrumental methods =‫تموت ترى ازعل عليك وا‬3 : ‫لـ ضميري الدراسي‬ Gravimetric Volumetric methods methods ‫تدريجية‬ Titration: The process of gradual addition of the standard solution with known concentration, which is called titrant to the unknown, which is ‫تحليلي‬ called analyte until the reaction is complete by reaching the end point. Q : What is the end point of the reaction and how does it appear? End point: It is the point at which the completion of the reaction appears and can be obtain by using indicators. Q : What are the indicators?  Indicators: Complex organic compounds that change color with changing pH. Q : What is the equivalent point of the reaction ? Equivalent point: It is the point where the quantity of the standard substance is equal to the quantity of the unknown substance (equal to the number of moles) during the titration. Q : What is the difference between the equivalence point and the end point of the reaction, and which is greater? 1. The equivalence point occurs first when the amount of the unknown and known substance is equal, and then no change in color occurs. 2. The end point occurs after the equivalence point, at which point the color of the solution changes. ‫ماما انت بس ركز وبعون ا= نرسب سويه‬ ‫اكبر‬ 3. The end point is greater than the equivalence point. Q : What are the conditions for titration? 1- the reaction must be balanced 2HCl + Na2CO3 2 NaCl + H2O + CO2 2- the reaction should be rapid and not lead to side reactions. 3- when the reaction is complete, the solution shows a clear change in one of its properties, such as pH. ***There are four types of reactions used in the titration: 1- acid- base reactions (Neutralization). NaOH + HCl NaCl + H2O 2- Oxidation- reduction reaction (Redox). MnO4- + 5 Fe +2 + 8H+ Mn+2 + 5 Fe+3 + 4 H2O 3- Precipitation reaction. AgNO3 + NaCl AgCl + NaNO3 4- complex formation reactions. EDTA + Ca+2 Ca-EDTA Acid- Base Titration Acid- Base titration or neutralization means complete reaction of acid with base to form water and salt. HCl + NaOH ‫عايير‬E‫وحد ا‬ NaCl + H2O When titration is used to standardize an acid solution, we use  few drops of indicators to distinguish the end point. Acid- base indicators are complex organic compounds that exist in two different forms of color depending on whether they are in acid, base or ‫وسط محايد‬ neutral medium. For example, methyl orange is yellow in alkaline or neutral conditions but it is red in acidic medium. The first change in the color of the indicator means the end of the titration (end point) which used in the calculations. Standardization of HCl solution ‫م‬ The concentrated HCl is about (11-12)‫تقرار‬M, this acid can't used as a ‫ن‬ ‫مك‬ ‫عدم اس‬ ‫يج‬ primary standard solution due to its volatility. So it is not possible to ‫يم‬ ‫تخفيف‬ ‫نها‬ prepare the primary standard solution from acid by dilution of the CQ M concentrated, and it must be titrated against primary standard solution. Conditions of primary standard solutions and secondary standard solutions ‫اقراها يجوز يجي منها شي‬ Primary standard materials Secondary standard 1-‫ئب‬Very pure, free of materials ‫الشوا‬ impurities. 1-Not 100% pure. 2-Its concentration is precise 2-Affected by weather and does not change over conditions. time. ‫اعتمد عليها‬ 3-It cannot be relied upon to 3-Its molecular weight is estimate unknown high, so the error resulting compounds because an from the weight is small. approximate, inaccurate 4-Not affected by weather weight is used during conditions (temperature, preparation. light, humidity).  Procedure: 1-0.5 g of pure Na2CO3 (primary standard) is dissolved in 100 ml distilled water in 100 ml in volumetric flask. 2- Fill the burette by HCl solution. 3-Place 5 ml of Na2CO3 solution in a clean conical flask, then add 1 drop of methyl orange solution as indicator. 4-Titrate with HCl solution until the color changes from yellow to red (this is the end point). 5-Repeat steps 3&4 twice then find the exact volume of HCl required for the neutralization. 6-Use the relation N1V1 HCL = N2 V2 Na2CO3 from this relation the unknown N of HCl can be calculated. 7-Use HCl solution to find the concentration of unknown solution of Na2CO3 by repeating the previous steps. Results and Calculations ‫هاي من ايام سادس‬ N= ‫ضارب وياها وحدك‬ Eq. wt. = 1- Equivalent wight of Na2CO3 = = 53 2- N= For Na2CO3 3- N1V1 (HCl) = N2 V2 (Na2CO3) ? × read on burette = 0.094 × 5 N1 = ? ( the Normality of HCl) N1V1 (HCl) = N2 V2 (Na2CO3) N1 × read on burette = ? × 5 4- N = Wt. = ? gm of Na2CO3 which dissolved in 100 ml distilled water : ‫ط"ب الطب حالًيا‬