Experiment 3: Water of crystallisation in Iron II sulphate

To analyse iron (II) sulphate to find the number of molecules of water of crystallisation per unit formula

Notes

Potassium manganate (VII) is a self indicating reagent for titrations. It will oxidise iron II to iron III according to the equation:

MnO4- + 5Fe2+ + 8H+ Mn2+ + 5Fe3+ + 4H2O

Consequently the ratio is one mole of manganate VII ions are equivalent to 5 moles of Fe2+ ions

Instructions

Prepare a potassium manganate (VII) solution of between 0,01 and 0,02 molar. Use this to find the molarity of a self prepared solution of Iron II sulphate and hence the number of moles of water of crystallisation per unit formula.

This experiment could be used for planning (b) and so all stages should be carefully explained

Experimental report

The following factors must be considered:

• Accurate recording of raw data
• Choice of suitable apparatus and method
• Presentation of raw data
• Data analysis and presentation
• Evaluation of errors both qualitative and numerical

Assessment

• Data collection
• Planning (b)
• Data analysis
• Evaluation