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Tripoli Campus
Chem 200 Lab Report
Experiment 6 : Redox titration
Course Instructor: Dr Lisa Diab
Student Name: Marwa Noaman ID: 51230262

Introduction: To determine a substance analytically, oxidation- reduction reactions are used. During any redox reaction transferring of reactions occurs from a reducing agent to an oxidizing agent.
Purpose:
* To titrate "Mohr's salt" solution with KMNO4,(second standard) which has to be standardize with oxalic acid (first standard). * To learn how acid-base reactions could be used in titration analyses of unknown substances with basic components. * To standardize potassium permanganate solution KMNO4, which then be used for titration of iron unknown solution. * To write the net ionic equations of redox reaction carried out in this experiment. * Concept of experiments: * A standard KMNO4 solution, used in this experiment as titrant, cannot be prepared directly by dissolving of a known amount of solid KMNO4 because this reagent is a very strong oxidizing agent. Solutions of potassium permanganate are unstable and their concentration changes slowly from time to time. * In this experiment a standard solution of 0.1 N oxalic acid is used for the standardization KMNO4, potassium permanganate oxidizes oxalic acid (C3+) to carbon dioxide (C4-) and water while itself being reduced to Mn2+. Chemicals, Glassware, Equipment Required:
Chemicals: Potassium permanganate, ferrous ammonium sulfate (Mohr's salt), 1M sulfuric acid, and 0.1N oxalic acid solution.
Glassware: 50ml burette, 250ml Erlenmeyer flask , 10ml graduated pipette ,100 and 250ml beakers, graduated cylinder, funnel.
Equipment: ring stand with a clamp for burette, Bunsen burner, safety glasses, marking pen.
Procedure:
it is the same as manual. A) Standardization of a KMNO4 solution by titrating it against an oxalic acid solution:
Data and calculation:
Mass of oxalic acid acid=1.5068
Volume=250ml
[H2SO4]=1M
Average volume of KMNO4=(6.1+6.2)/2=6.15ml
Heating 60 degree Celsius.
[KMNO4]=???
Reduction: MNO4- +8H+ + 5e- ----------> Mn2+ + 4H2O (x2)
-------------------------------------------------
Oxidation: C2O42- -----------> 2CO2 + 2e- (x5)
5 C2O42- + 2 MNO4- + 16 H+ --------------> 2 Mn2+ + 10CO2 + 8 H2O
At equivalent point: n MNO4-/2= n C2O42-/5 n C2O42-=m/M=1.5068/126.1=0.012mole [C2O42]=n/v= 0.012/250x10-3=0.048M n MNO4-/2= n C2O42-/5
[ MNO4-]xVMNO4/2-= [C2O42-]xVC2O42-/5=
[ MNO4-]=[C2O42-]xVC2O42-x2/ VMNO4x5=0.78M
Result: [ MNO4-]=0.78M B) Analysis of an iron unknown Mohr's salt solution:
[H2SO4]=1M.
M (ammonium iron 3 sulfate 6 hydrate)= 392.14g.mol-1
[ MNO4-]=0.78M.
Average volume of MNO4-=(4.5+4.5)/2=4.5
Reduction: MNO4- +8H+ + 5e- ----------> Mn2+ + 4H2O (x1)
-------------------------------------------------
Oxidation: Fe2+ ------------> Fe3+ + 1e-1 (x5)
MNO4- + 5 Fe2+ + 8H+ ----------> Mn2+ + 5 Fe3+ + 4H2O
At equivalent point: n MNO4-/1=n Fe2+/5
Cb.Vb=(CFe2+.V Fe2+)/5 CFe2+=5 Cb.Vb/ V Fe2+
CFe2+=5(0.78).(4.5)/10=1.755M
Results: CFe2+=1.755M

Discussion: 1. Human error. 2. Error while filling the burret not to the zero exactly. 3. Error in calculations in the equivalent point since we did not take drop by drop from burrete.

Questions: 1. why do we heat ? high temperature is considered as catalyst that increase the rate or speed of reaction. 2. Why do we use H2SO4?
H2SO4 is strong acid and will deliver H+ which will help to proceed the reaction much faster. 3. Can we use HCl or HNO3 ?
No we cannot used both because:
CL- ions of HCL will be oxidized by KMNO4, reducing the effectiveness of titration.
HNO3 is a good oxidizing agent and will oxidize Fe2+ to Fe3+.