1. EXP.NO.5 Redox Titration ( Oxidation Reduction Titration) A-preparation and standardization of KMnO4 soln. B- determination of [Fe2+] in unknown sample.
Equipment required
Balance
Beakers (100 mL, 250 mL)
Volumetric flask (100 mL,250 mL)
Storage bottle (approximately 250 mL)
Pipette (10 mL)
Burette
Stand and clamp
Funnel
Conical flask (250 mL)
Chemecals
Potassium permanganate solution [KMnO4] 0.1N
Sodium oxalate[Na2C204.2H2O] 0.1N
H2SO4 2N
Unknown Solution of ( Fe +2 )

2. Safety
Using oxidizing agents (KMnO4), reducing agents (Na2C2O4) and unknown Fe(II) salt), and acids (H2SO4 ). These are irritants.
Wear your goggles at all times. Immediately clean all spills. If you do get either of these in your eye, immediately flush with water.. Ask your instructor if you ever have any questions about safety.

3. A/ preparation and standardization of KMnO4 soln.
PROCEDURE:
A/ preparation and standardization of KMnO4 soln.
B/ determination of [Fe2+] in unknown sample.
A/ preparation of KMnO4 soln.
1- Weigh out on a rough balance (0.32gm of solid KMnO4 on a watch glass, transfer it to a beaker by addition of 50 ml D.W.
2- Cover the beaker by watch glass, boil gently for 15min. ,cool to room temperature.
3- Filter the soln. through glass wool to a well cleaned 100ml –volumetric flask. and complete the volume by D.W.
Preparation of standard solution of 0.1N Na2C2O4
1- Weigh out on a sensitive balance (0.6700gm) of pure solid Na2C2O4.
2- Transfer it to a beaker by adding 30ml D.W, add 40ml of (2N H2SO4) soln.
3- Transfer quantitatively to a 100ml –volumetric flask, and complete the volume by D.W.
Standardization of KMnO4 soln.
1- Fill the burette after washing it by D.W, with KMnO4 soln.
2- Pipette 10ml of the prepared 0.1N Na2C2O4 soln. to a conical flask, heat to 60C.
3- Titrate with KMnO4 soln. from burette very slowly and with constant stirring until the color change from colorless to violet . Repeat the titration twice, record the volume of KMnO4. and calculate the N of KMnO4 soln.

4. A/ Standardization of KMnO4 soln.
Calculations:
The no. of meq.wt. of Sodium oxalate= The no. of meq.wt. of permanganate at the end point.
N x V (Sodium oxalate) = N' x V' (KMnO4)
From this relation calculate the normality of KMnO4
gm/L of KMnO4 = N' x eq. wt. KMnO4
B/ determination of [Fe2+] in unknown sample.
1- Fill the burette after washing it by D.W, with std. soln. of KMnO4 soln.
2- Pipette 10ml of the prepared unknown [Fe2+] sample soln. . Add 5ml of 2N H2SO4 soln.
3- Titrate with KMnO4 soln. from burette very slowly and with constant stirring until the color change from colorless to violet . Repeat the titration twice, record the volume of KMnO4. and calculate the N of [Fe2+] soln. and gm /L of [Fe2+] in sample
Calculations:
The no. of meq.wt. of KMnO4 = The no. of meq.wt. of Fe2+ in sample at the end point.
N x V (KMnO4 )= N' x V' (Fe2+ in sample )
From this relation calculate the normality of Fe2+ in sample
gm /L of Fe2+in sample = N' x eq. wt. Fe

5. Potassium Permanganate
Oxidation is a loss of an electron or electrons by an atom or group of atoms.
Reduction is a gain of an electron or electrons by an atom or group of atoms.
Potassium Permanganate
1) Potassium permanganate is a purple coloured solid.
It is NOT a primary standard as it cannot be obtained
in a state of very high purity and it decomposes in the
presence of sunlight.
2) Potassium permanganate acts as an oxidising agent
by gaining 5e- in acidic solution:
Half Reaction:
MnO H e- Mn H2O
(+7) (+2)
Purple Colourless

7. Na2C2O4 Sodium oxalate is a primary standard substance
A primary standard substance should be % pure although a 0.01% to 0.02% impurity is tolerable if it is accurately known.
A primary standard substance should be stable at drying temperatures, and it should be stable indefinitely at room temperature. (A primary standard substance is always dried before weighing, unless it is a hydrate.)
It should be readily available.
It should have a relatively large formula weight. Therefore, a relatively large mass of it will be weighed for titration. This will reduce error.

8. The following points about this reaction should be noted:
1- The reaction occurs only in acid solution. Acidification is achieved by the addition of sulfuric acid ( H2SO4 2N)
2- The reaction rate is normally slow but in this experiment is increased;
a- by warming the contents of the conical flask
b- because the reaction is catalyzed by the presence of manganese (ll) ion, which is a product of the reaction
3- No indicator is necessary in the titration. As the permanganate solution is run into the sodium oxalate solution the purple MnO4- ion is reduced to the effectively colorless Mn2+ ion. When the addition of one drop of permanganate solution to the conical flask produces a permanent pink color, this indicates that there is no remaining sodium oxalate capable of reducing the Mn04- to Mn2+, and therefore that the end point has been reached. (KMnO4) is self-indicator
4- The faint pink MnO4– end point does not occur at the equivalence point. This end point occurs a fraction of a drop after the equivalence point. This error is small and can be corrected with a blank, or during standardization.
How would you use a blank to correct this error?
The volume of MnO4– used to reach the end point during the titration of distilled water (a blank) is subtracted from all standards and all samples.

10. Applications of Potassium Permanganate – Iron(II) Titrations
Iron is an important element in our bodies as it forms part of the haemoglobin molecule in our blood. Haemoglobin is the molecule responsible for transporting oxygen in our blood. The oxygen actually
becomes attached to the iron atom in the haemoglobin molecule. Our bodies can easily become deficient in iron resulting in anaemia. This condition can be remedied with a change in diet and a course of iron tablets (FeSO4)In the next experiment we will attempt to calculate the amount of iron(II) sulphate in iron tablets
When preparing (FeSO4)it must be dissolved in water containing dilute sulphuric acid: -the sulphuric acid prevents the Fe2+ ions reacting with water to form a new substance prevents hydrolysis
- the sulphuric acid helps to prevent the Fe2+ ions being oxidised to Fe3+ ions by the oxygen in the air or dissolved in the water
Haemoglobin Molecule

11. MnO4–(aq) + 8H+(aq) + 5Fe2+(aq) → Mn2+(aq) + 4H2O(l) + 5Fe3+(aq)
After the KMnO4 is standardized, we will measure the Fe(II) content of an unknown salt.
MnO4–(aq) + 8H+(aq) + 5Fe2+(aq) → Mn2+(aq) + 4H2O(l) + 5Fe3+(aq)
What is oxidized?
The Fe is oxidized from +2 to +3.
What is reduced?
The Mn is reduced from +7 to +2.

12. KMnO4 – oxidising agent – when added to an
acidified (to ensure Mn+7 is reduced to Mn+2)
solution containing Fe2+ ions it converts the Fe2+ ions
to Fe3+ ions. Reactions involved:
Oxidising Agent (itself reduced):
Reducing Agent (itself oxidised):
(B) Fe2+ - e Fe3+
Adding these two half equations:
(A ) MnO H e Mn H2O
MnO H Fe Mn Fe H2O