Laboratory report about Conductometric titration on Instrument Analytic, assignment for Industry Process report, Chemical Engineering.
Complexometry Titration and its Application B. PURPOSE : 1. To make and determine (standardization) of Na-EDTA solution 2. To determine the total hardness of Kenjeran well waterFull description
Chemistry
Experiment 8 - Complexometric Titration
Chemistry Laboratory
Instructor: Huynh Kim Lam
EXPERIMENT # 3
REDOX TITRATION WITH KMnO4 I. INTRODUCTION
In an oxidation-reduction or redox reaction, there occurs an exchange of electrons between to reactants, resulting in the changes of oxidation number. The substance that gains electrons is said to be reduced, therefore, it is called the oxidizing agent. The substance that loses electrons is called the reducing agent, thus it is oxidized. One gram equivalent weight (GEW) of oxidizing agent is the 23 weight that gains 6.02x10 electrons and one gram equivalent weight of reducing agent is the weight 23 that loses 6.02x10 electrons. According to the definition of gram equivalent weight, one GEW of oxidizing agent reacts with one GEW of reducing agent. GEWox
=
GEWed
Consider the reaction of potassium permanganate with oxalic acid (H 2C2O4) in the presence of excess sulfuric acid. The balanced molecular and net ionic equations are: 2KMnO4 + 5H2C2O4 + 3H2SO4
10CO2 + K2SO4 + 2MnSO4 + 8H2O +
2MnO4 + 5H2C2O4 + 6H
10CO2 + 2 Mn
2+
+ 8H2O 2+
The oxidation number of Mn in MnO 4 is +7 while it is +2 in Mn . Hence, each Mn undergoes a change in oxidation number of five. Since each formula unit of KMnO4 contains one Mn, and each Mn gains five electrons, one mole of KMnO 4 is five gram equivalent weights in this reaction. As a result, KMnO4 produces 5 moles of electrons per mole of KMnO 4 or has five equivalents per mole of KMnO4. Thus, the gram equivalent weight of KMnO 4 in this reaction is 31.60 grams.
GEW of KMnO4 =
158.0 g 1 mole 31.60 g × = 1 mole 5 eq eq
The oxidation number of carbon in H 2C2O4 is +3 while it is +4 in CO 2. Thus each carbon undergoes a change in oxidation number of one. However, each formula unit of H 2C2O4 contains two carbons, and since each carbon loses one electron, one mole of oxalic acid is two gram equivalent weights in this reaction. Consequently, H2C2O4 produces 2 moles of electrons per mole of oxalic acid or has two equivalents per mole of oxalic acid. The gram equivalent weight of H 2C2O4 is 45.0 grams GWE of H2C2O4 =
90.0 g 1 mole 45.0 g × = 1 mole 2 eq eq
Summer 2011 – Revision 4/3/2012
1
Chemistry Laboratory
Instructor: Huynh Kim Lam
In this experiment, you will prepare an approximately 0.05N KMnO 4 solution and standardize this solution by titrating against a standard solution of H2C2O4 (primary standard). Then the standardized KMnO4 solution (secondary standard) will be used to determine the concentration of unknown oxalic +2 acid solution and unknown Fe solution. For redox titrations, the number of equivalents of oxidizing agent must be equal to the number of equivalents of reducing agent. For the reaction of KMnO 4 with H2C2O4: eq of KMnO4 = eq of H2C2O4 Alternatively, this relationship can be expressed as follows: Voxidizing x Noxidizing = Vreducing x Nreducing Where V is the volume of oxidizing or reducing agents used in titrations And N is the normality of oxidizing or reducing agents. At the end of a titration, three of the four variables will be known and the unknown variable can be determined. II. LEARNING OBJECTIVES
- Learn about the term of gram equivalent weight - Review of oxidation-reduction reactions - Standardize the concentration of KMnO 4 solution and determine the oxalic acid normality. III. EQUIPMENT AND REAGENTS 1. EQUIPMENT One 50 mL burette One 100 mL graduated cylinder Three 250 mL beakers One 10 mL volumetric pipette Three 250 mL Erlenmeyer flasks One glass watch One funnel (small size) One stirring rod One medicine dropper Water bath
Summer 2011 – Revision 4/3/2012
2. REAGENTS 0.05N KMnO4 (Potassium permanganate) 0.1N Oxalic acid (H 2C2O4) 6N H2SO4 Distilled water Unknown concentration solution of KMnO 4 Unknown concentration solution of H 2C2O4 Unknown concentration solution of FeSO 4 in H2SO4
2
Chemistry Laboratory
Instructor: Huynh Kim Lam
IV. EXPERIMENTAL PROCEDUE
1. Prepare KMnO4 solution: (TA will prepare it for you but you have to understand the procedure) Weight 1.58g KMnO₄ Transfer it to a 250-mL beaker with 100-mL of DW Mix the solution thoroughly by vigorous swirling Transfer the solution into a 250-mL volumetric flask and fill with DW Then transfer it to a dark brown bottle 2. Handling with burette: Clean the burette with distilled water Rinse it three times with 5 mL prepared KMnO4 solution. Discard the rinse solution. Fill the burette with KMnO4 solution and allow it to drain through the burette tip until no air bubbles remain in the tip. Record the burette reading before beginning the titration. Note: as the KMnO 4 solution is dark color, read the burette at the top of the meniscus.
3. Standardization of prepared KMnO 4 solution: Prepare 10 mL of standard oxalic acid solution into each of three 250 mL Erl enmeyer flasks. Add 40 mL of distilled water to each flask. Add 20 mL of 6N H 2SO4 solution to each flask (fume hood). 0 Warm the flasks in the water bath 85 C – 90 C Titrate the hot solutions against the KMnO 4 solution. ˚
Note: the KMnO4 solution should be added very slowly initially. Endpoint for this experiment refers to the titrate volume needed to keep the faint pink color throughout the stirred solution for at least twenty seconds. Record the burette reading and calculate the normality of the KMnO 4 solution.
4. Determination of unknown concentration H 2C2O4 solution: Prepare 10 mL of unknown concentration solution of H 2C2O4 into each of three 250 mL Erlenmeyer flasks. Add 40 mL of distilled water to each flask. Add 20 mL of 6M H₂SO₄ solution to each flask (fume hood). Warm the flasks in water bath 85 C - 90 C. Titrate the hot solutions. Calculate the normality of the unknown concentration H 2C2O4 solution; determine the average and the standard deviation. ˚
˚
5. Determination of unknown concentration FeSO 4 solution: Prepare 10 mL of unknown concentration solution of FeSO 4 solution into each of three 250 mL Erlenmeyer flasks. Add 40 mL of distilled water to each flask. Add 20 mL of 6M H₂SO₄ solution to each flask (fume hood). Warm the flasks in water bath 85 C - 90 C. Titrate the hot solutions. Calculate the normality of the unknown concentration H 2C2O4 solution; determine the average and the standard deviation. ˚
