Review A-Level Edexcel Chemistry Group 7 redox through halogen displacement, ionic equations and colour changes in aqueous and organic layers.
lodine can be extracted from seaweed. The seaweed is heated strongly to burn off the organic matter. The resultant ash is boiled in water to dissolve the iodide ions, and the mixture is filtered.
The iodine is separated from the aqueous solution using solvent extraction. The aqueous solution is mixed with cyclohexane in a separating funnel, forming two layers.
The mixture is then shaken gently and left until the layers separate.
Most of the iodine dissolves in the cyclohexane layer.
State the colour of each layer after separation.
Aqueous layer
Cyclohexane layer
(b)(ii)
An explanation that makes reference to the following points:
Cyclohexane and iodine form London forces (between molecules) (1)
Hydrogen bonds between water molecules are stronger than London forces (between iodine and water molecules so less soluble in aqueous layer)
(1)
Allow 'van der Waals' / dispersion forces / instantaneous dipole - induced dipole forces
Allow 'Hydrogen bonds in water are strong'
Allow one mark for answers that compare type of attraction without any reference to magnitude or answers based solely on polarity
e.g. Just 'iodine forms London forces with cyclohexane but cannot form hydrogen bonds with water' scores 1 mark
'iodine and cyclohexane are non-polar, but water is polar' scores 1
e.g. ‘Intermolecular forces formed by iodine and water are weaker than intermolecular forces in water' scores 1
(2)