Title: Standardization of potassium permanganate solution by ammonium iron (II) sulphate
Name: Toh Zi Xin
Name of partner: Wong Jing Hui, Gan Chun Yiang,
Wong Teck Jun
Lecturer: Dr. Neo Kian Eang
Practical class: P4
Potassium permanganate solution can be standardized by titration against a standard solution of ammonium iron(II) sulphate solution. This is an example of standardization, which is a process to determine the concentration of a solution by using it to titrate another solution which have a known concentration. This titration is known as redox titration as the titrant, which is the potassium ...view middle of the document...
This is because it is much less easier to be oxidizes in air to Fe3+, can be obtain in high state of purity and has a high molar mass. The oxidation of Fe2+ is depend on pH and it will be more readily occur when the pH is high. Thus, sulphuric acid is added to reduce the pH of the solution in order to reduce the oxidation of Fe2+.
Objectives: To standardize potassium permanganate solution by ammonium iron (II) sulphate.
1. About 3.9g of ammonium iron (II) sulphate was weighed accurately in 4 decimal places with a clean and dried 100mL beaker using analytical balance.
2. The salt was dissolved in distilled water ( ̴ 50 mL) and the solution was transferred to a 100mL volumetric flask.
3. The beaker was rinsed with small quantity of distilled water.
4. The flask was stoppered and shook well.
5. Distilled water was added to make up the volume to the mark by using a dropper.
6. The flask was stoppered and shook well by inverted the flask repeatedly. The molarity of ammonium iron (II) sulphate was calculated.
7. 25cm3 of the ammonium iron (II) sulphate was pipetted into a conical flask.
8. 15cm3 of 1M sulphuric acid was added.
9. The potassium permanganate solution was titrated until the first permanent pink colouration is observed.
10. The first conical flask was kept as reference and the titration were repeated twice.
a) Calculation of result
Titration number | 1 | 2 | 3 |
Initial volume of burette (cm3) | 0.00 | 0.00 | 0.00 |
Final volume of burette (cm3) | 25.00 | 24.90 | 25.00 |
Total volume of burette (cm3) | 25.00 | 24.90 | 25.00 |
Average volume of KMnO4 required for titration = 24.97cm3
Mass of ammonium iron (II) sulphate, Fe(NH4)2 (SO4)2·6H2O used = 3.9027g
Molar mass of ammonium iron (II) sulphate, Fe(NH4)2 (SO4)2·6H2O = 392.05 g/mol
No. of mole of ammonium iron (II) sulphate = Mass of ammonium iron (II) sulphate
Molar mass of ammonium iron (II) sulphate
= 3.9027g392.05 g/mol
= 0.01 mol
Molarity of ammonium iron (II) sulphate solution = No. of mole of ammonium iron ( = 2 \* ROMAN II) sulphateVolume
= 0.01mol0.1 L
= 0.1 M
∴ Thus, the molarity of ammonium iron (II) sulphate solution in the volumetric flask is 0.1M.
Molarity = No. of moleVolume
No. of mole = Molarity × Volume
No. of mole of ammonium iron (II) sulphate in conical flask = 0.1 M × 0.025 L
= 0.0025 mol
The overall equation is :
MnO4- + 8 H+ + 5 Fe2+ → Mn2+ + 5 Fe3+ + 4 H2O
From this equation, 1 mole of MnO4- ions react with 5 moles of Fe2+ .
No. of mole of KMnO4 required to reach the end point = No. of mole of ammonium iron = 2 \* ROMAN IIsulphate in conical flask 5