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ACID-BASE TITRATIONI. ObjectiveStudents can acquire knowledge and ability in determining concentration of the solution by divalen acid-base titration (H 2SO 4) by using phenoltalein indicator (PP).II. TheoryAccording to Br o nsted and Lowry, an acid is a species which donates a proton, H +, and a base is a species which accepts a proton in a proton-transfer reaction.For example, in the following acid-base reaction:H 2SO 4 (aq) + 2NaOH (aq) → 2H 2O (l) + 2Na + (aq) + SO 4 2 – (aq)H 2SO 4 (aq) is an acid which donates a proton, H +, to the base NaOH (aq).
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This reaction is often called a neutralization reaction.An acid-base titration is a procedure for determining the concentration of an acid (or a base) in a solution by measuring the volume of base (or acid) of a known concentration that completely reacts with it.The solution of accurately known concentration is called the standard solution (titrant), it contains a definite number of gram-equivalents per liter. Standard solution is usually added from a graduated vessel called a burette. The process of adding titrant until the reaction just complete is termed a titration and the substance to be determined is titrated (analyte). The point at which the reaction is complete is called the equivalence point or the theoretical (or stoichiometric) end point. This point must be detectable by some change unmistakable to the eye and this can be done by adding an auxiliary reagent, known as an indicator which should give a clear visual change (color change) in the liquid being titrated.In order to perform a titration procedure a reaction must fulfill the following condition.1. It must be simple reaction, which can be expressed by a chemical reaction. The substance to be determined should react completely with the titrant in stoichiometric or equivalent proportions.2.
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The reaction should be practically instantaneous or proceed with very great speed.3. There must be a marked change in some physical or chemical property (as color change) of the solution at the equivalence point.4. An indicator should be available which, by a change in physical properties (Color), should sharply define the end point of the reaction.5. If no visible indicator is available for the detection of the equivalence point, the latter can often be determined by other method as potentiometer or conduct metric or spectrophotometer titration.Titration can be used for many types of reactions:a.
Neutralization (reaction of acid with base.).b. Precipitation reaction.c. Oxidation – reduction reactionsd. Complex formation reactions.III. Materials and equipmentsv MaterialsNaOH solution 0,1 NH 2SO 4 solution x NP henolphthalein Indicator (PP)v EquipmentsBurette 50 mL 1 pcsErlenmeyer flask 250 mL 2 pcsDrooping Pipette 2 pcsGraduated Glass Cylinder 50 mL 2 pcsStirring Stick 1 pcsFunnel 1 pcsVolumetric Pipette 10 mL 1 pcsStand, retort and klem (stative) 1 setIV.
Mmol ion H + = mmol ion OH –Ma. VbInformation: Ma = acid molarity H XAMb = strong base molarity L(OH) nVa = acid volumeVb = base volumeX = acid valencen = base valenceAccording to The Theory:To determine NaOH solution’s volume that needed:T itra nt ( NaOH ) that used: 0,1 N same as 0,1 M ( because it is monovalen).Titrated ( H 2SO 4 ) that used: 0,1 N same as 0,05 M ( because it is divalen). This concentration is acquired based on the calculation H 2SO 4 concentration that made by group 2 and laboratory assistant.Ma. 2.10 mL = 0,1 M.
Vb1 mL = 0,1. VbVb = 1 mL / 0,1= 10 mLSo, to calculate H 2SO 4 0,05 M need 10 mL NaOH 0,1 N ( based on the th eor y )Based on the experiment’s result:Experiment I ( needed NaOH around 0,96 mL)Ma. 10 ml = 0,1 M.
20 ml = 0,96 mmolMa = 0,96 mmol/20 ml= 0,048 MExperiment II ( needed NaOH around 0,91 mL)Ma. 10 ml = 0,1 M. 20 ml = 0,91 mmolMa = 0,91 mmol/20 ml= 0,0455 MExperiment III ( needed NaOH around 0,94 mL)Ma. 10 ml = 0,1 M.
20 ml = 0,94 mmolMa = 0,94 mmol/20 ml= 0,047 MCalculate using average volume:Ma. 10 ml = 0,1 M.
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