Separation Techniques Solvent Extraction Extraction of iodine from seaweed Seaweed contains a wide range of elements drawn from seawater by the living algae giving concentrations in the organism that may be considerably higher than in seawater itself In the past this natural concentration ID: 501750
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L3 BTEC Applied Science: Unit 4Separation Techniques
Solvent ExtractionExtraction of iodine from seaweed
Seaweed contains a wide range of elements drawn from sea-water by the living algae, giving concentrations in the organism that may be considerably higher than in sea-water itself. In the past, this natural concentration of useful elements, for which there was then no other economic source, gave rise to a large scale ‘cottage industry’ network around the west coasts of Britain and Ireland, employing thousands in gathering and burning the kelp on the shore. The two principal products were soda ash (sodium carbonate) for the alkali industry in the 18th and early 19th centuries, and iodine in the later nineteenth century. Kelp was also used, and still is, as an excellent fertiliser. Soda ash production from kelp ceased when the chemical industry itself found ways of producing sodium carbonate from sodium chloride, and iodine production from kelp ceased when the extraction of iodine from Chile saltpetre became dominant. In both events, thousands were put out of work, leading to large numbers emigrating from Scotland and Ireland to America and elsewhere. Nowadays, a small-scale industry continues, providing the raw material for expensive kelp-derived health supplements containing several ‘essential minerals’ including iodine. A typical kelp capsule may contain 0.1% iodine. The main kelp product at present, though, is for alginates used in food and drink, cosmetics and dozens of other everyday products.
AimYou are going to extract iodine from some laminaria seaweed (kelp) using the process of solvent extraction
EquipmentLaminaria seaweed (kelp)Bunsen burnerTongsBeaker x 2FunnelFilter paperConical flaskDilute sulphuric acid1.5M hydrogen peroxide (25ml)20ml CyclohexaneTap funnelRetort stand, boss and clampBasinKettle
Method for TEACHER DEMOAssemble all the apparatus you will need. You will need to follow the procedure below:In a fume cupboard, burn a quantity of Laminaria seaweed (kelp) to ashGently heat a quantity of the ash in a beaker of water to dissolve the iodineFilter this into a conical flask using a funnel and filter paperAdd a few drops of dilute sulphuric acid and approximately 20ml of the 1.5M hydrogen peroxideNext, put 20ml cyclohexane in a tap funnelAdd the filtrate from the conical flask to the cyclohexanePlace a stopper in the tap funnel and shake, periodically removing the stopper to relieve pressure build upWhen the water has become clear and the cyclohexane layer has turned red place the tap funnel into a clamp on a retort stand and allow layers to settleRun off the water layer into a beaker and discardNext, run off the cyclohexane layer into a second flaskLeave the cyclohexane layer to evaporate in the fume cupboard (DO NOT USE NAKED FLAME)Evaporation rate can be increased by immersing the flask in a basin of hot water
SafetyWear eye protection at all timesUse of fume cupboard is vitalCaution when shaking the tap funnel – pressure will build so remove stopper at regular intervalsNo naked flames near cyclohexaneSlide2
ObservationsWhy did we burn the kelp to ash?___________________________________________________________________________________Why was the use of cyclohexane important to obtaining the iodine?_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________Research: When and how was iodine discovered?______________________________________________________________________________________________________________________________________________________________________Further ContextHow does your experiment link to the real world?_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
How could this experiment be altered to be conducted on a larger scale?_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________