Titration is a widely used technique in chemistry practicals to determine the concentration of a solution. It involves reacting a known solution, called the titrant, with an unknown solution, called the analyte, until a reaction endpoint is reached. This allows for the determination of the concentration of the analyte solution.
Titration – Exam Practice for Determining Water of Crystallization in Fe(NH4)2(SO4)2.xH2O
The aim of this chemistry practical is to determine the value of x in the formula FFe(NH4)2(SO4)2.xH2O by titration against a standard solution of potassium manganate (VII) (permanganate).
- Pipette, 25 cm³
- Pipette filler
- 3 conical flasks, 250 cm³
- Ammonium iron(II) Sulfate solution, A (IRRITANT)
- Sulfuric acid, dilute, 1 M H₂SO₄
- Burette, 50 cm³
- Funnel, small
- Potassium manganate (VII) solution, B (0.01 mol dm⁻³) (LOW HAZARD)
- White tile
- Wash-bottle of distilled water
In this experiment, 25 cm3 of ammonium iron(II) sulfate solution, A, is pipetted into a conical flask and an equal volume of dilute sulfuric acid is added. The solution is then titrated with potassium manganate (VII) solution, B, until a permanent faint pink color appears. The titration is repeated twice, and the results are recorded in the results table.
The obtained results are used to calculate the value of x in Fe(NH4)2(SO4)2.xH2O. The concentration of Fe2+ ions is calculated from the titre and the reaction equation. From the concentration, the mass of anhydrous Fe(NH4)2(SO4)2 in one liter of solution is calculated. The mass obtained in the previous step is subtracted from the mass of the salt in one liter, which gives the amount of water of crystallization in mol of the salt. The amount of water in 1 mol of the salt is x mol.
- From the titre and the equation for the reaction calculate the concentration of Fe2+ ions (y mol dm-3).
- From the concentration calculate the mass of anhydrous Fe(NH4)2(SO4)2 in one litre of solution.
- Subtract the mass obtained in step 2 from the mass of the salt in one litre. This difference, z g, divided by 18 g mol-1 gives the amount of water of crystallization in y mol of the salt.
- x mol is the amount of water in 1 mol of the salt.
This chemistry practical provides experience in the process of titration, which is an essential technique used in many areas of chemistry. The experiment aims to determine the value of x in Fe(NH4)2(SO4)2.xH2O by titrating the solution with potassium manganate (VII) solution. The obtained results are used to calculate the amount of water of crystallization in the salt.